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Computational Strategies in Therapeutic Antibody Development: Current Techniques and Future Directions

DOI : 10.17577/IJERTCONV13IS06006

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Computational Strategies in Therapeutic Antibody Development: Current Techniques and Future Directions

Abu Junaid Siddiqui1

a*Department of Bioengineering, Faculty of Engineering, Integral University, Lucknow, India

abujunaid@iul.ac.in

Prof. (Dr.) Alvina Farooqui 1*

Professor & Head of Department of Bioengineering, Faculty of Engineering, Integral University, Lucknow, India

alvina@iul.ac.in

Prof. (Dr.) Alvina Farooqui 1* are corresponding author.

Abstract

Antibodies are specialized proteins that identify and bind to specific molecular targets, playing a central role in the adaptive immune system. In autoimmune conditions, however, they may mistakenly target the body's own healthy tissues. Owing to their remarkable binding specificity and adaptability, antibodies have become the most prominent category of biotherapeutic agents, with monoclonal antibodies comprising a significant portion of the top-selling drugs globally. Recent developments in computational protein modeling and design are significantly contributing to the advancement of antibody- based therapies. These antibody-focused computational approaches are increasingly benefiting from large-scale datasets generated through next-generation sequencing technologies. Additionally, they are being applied to newer antibody formats, such as nanobodies. This review offers a comprehensive summary of current databases, established tools, and innovative methodologies in computational antibody research, with a focus on their relevance to therapeutic antibody design and engineering.

Keywords: homology modeling, therapeutic antibodies, molecular docking, antibodyantigen interactions, bioinformatics databases Introduction

  1. INTRODUCTION

    Antibodies, also known as immunoglobulins, are essential components of the adaptive immune system. They identify and bind to specific molecular structuresknown as antigenson potentially harmful entities for elimination [1]. In autoimmune disorders, however, these proteins may mistakenly target endogenous molecules, leading to immune responses against healthy tissues [2]. Antibodies have evolved to recognize a broad spectrum of antigenic surfaces, making them highly adaptable binding agents [3].

    Due to their specificity and adaptability, antibodies have become a cornerstone of therapeutic interventions and currently represent the largest category within the biotherapeutic market. Among the top-selling drugs globally are five monoclonal antibodies: adalimumab and infliximab (targeting TNF), rituximab (anti-CD20), bevacizumab (anti- VEGF), and trastuzumab (anti-HER2/neu), whose clinical impact continues to grow [4]. As the demand for effective antibody therapies increases, more efficient discovery and development strategies are needed. Computational approaches offer promising alternatives to traditional, labor-intensive

    experimental protocols, enabling rapid design and screening of therapeutic candidates [5].

    Several established bioinformatics toolssuch as homology modeling [6,7], proteinprotein docking [8,9], and interface prediction algorithms [10]are now routinely used in the rational design of antibodies [1113]. In addition, computational methods are being developed to evaluate critical features like immunogenic potential [14] and biophysical stability [15]. The availability of extensive datasets, including structural [16], sequence [17], and experimental data [1821], has significantly advanced data-driven antibody design.

    A transformative development in this context has been the application of next-generation sequencing (NGS) to characterize B-cell receptor repertoires [22]. NGS enables high-throughput profiling of antibody sequences, capturing millions of variants from the theoretically vast antibody diversity in humansestimated at 10¹² to 10¹ unique sequences [23,24]. Analysis of these repertoires reveals biases and patterns that reflect the natural variability and evolution of the immune system [25]. Such insights are invaluable for benchmarking therapeutic antibody candidates [13] and designing biologically inspired display libraries [26].

    Moreover, the growing arsenal of computational tools is now being extended to emerging antibody formats, such as nanobodies, which exhibit favorable biophysical traits like high solubility, stability, and reduced immunogenicity [27]. As a result, computational antibody modeling has matured into a robust discipline, capable of supporting a wide array of therapeutic development initiatives.

    This review provides an organized summary of current databases, algorithms, and tools used in computational antibody research. Emphasis is placed on their application in antibody design, structural prediction, and emerging strategies aimed at therapeutic innovation.

  2. Antibody Structure, Function, and Therapeutic Formats

    Immunoglobulins (antibodies) are synthesized by B lymphocytes in jawed vertebrates and serve as either membrane-bound B-cell receptors or secreted soluble antibodies. Each of the estimated 5×10 B cells in the human body produces a unique antibody variant through somatic recombination of variable (V), diversity (D), joining (J), and constant (C) gene segments [23,28,29].

    Heavy chains are assembled using V, D, J, and C gene segments from the heavy chain locus, while light chains are formed from V, J, and C segments located at the or light chain loci. These chains combine to form five major antibody isotypes: IgG, IgD, IgE (monomeric forms), IgA (dimeric), and IgM (pentameric) [30]. The IgG isotype, which predominates in blood circulation and has the most therapeutic relevance, contains one crystallizable fragment (Fc) and two antigen- binding fragments (Fabs).

    Each Fab fragment consists of a heavy (VH) and a light (VL) variable domain, which interact with a specific site on the antigen known as the epitope. These variable domains each contain three highly variable loopstermed complementarity- determining regions (CDRs)which make up the antigen- binding site, or paratope. During antigen exposure, B cells undergo somatic hypermutation within the CDRs, a process known as affinity maturation, resulting in higher-affinity antibodies [31]. Combined with the sequence variability introduced by V(D)J recombination, this process contributes to a theoretical antibody diversity of up to 10¹ variants [23,24].

    Although the CDRs are hypervariable in sequence, most (excluding CDRH3) adopt a limited range of backbone conformations, known as canonical structures [32]. CDRH3 is particularly diverse both in sequence and structure [33], and it plays a crucial role in antigen recognition [34,35]. Consequently, CDR regionsespecially CDRH3are often the primary targets in antibody engineering for monoclonal antibody (mAb) development [36,37].

    Despite their advantages, conventional mAbs (~150 kDa) often exhibit poor tissue penetration. To address this, smaller antibody derivatives and engineered formats have been developed. These include single-chain variable fragments (scFv), composed of linked VH and VL domains, and other modular structures such as diabodies and minibodies [3840]. Additionally, bispecific and multispecific antibodies engineered to bind two or more distinct antigensare gaining attention in cancer therapy [41].

    Another innovation in antibody engineering is the development of single-domain antibodies, also known as nanobodies or VHHs, which are naturally found in camelids and certain shark species. Nanobodies are approximately half the size of a standard antiboy domain but retain comparable specificity and affinity. Their high solubility, thermal stability, and lower immunogenic potential make them promising therapeutic agents [27]. Notably, caplacizumab, the first nanobody-based drug, received regulatory approval in 2018 [42]

    Antibody Databases

    The effectiveness of computational antibody research depends on access to well-curated and diverse datasets. Several resources provide detailed information on therapeutic antibodies, including the Therapeutic Antibody Database (TABS) and the SAbDab-Therapeutic Antibodies database [13]. These repositories can be categorized based on their contentsequence, structure, or experimental datawith some integrating all three types (see Table 1).

    Most databases include both conventional antibodies and nanobodies. However, there are specialized resources like sdAb-DB that focus exclusively on single-domain antibodies [58].

    Figure 1Antibody structure and binding. (A) Antibodies in soluble form often adopt the IgG isotype, a Y-shaped molecule consisting of two heavy chains (blue and amber) and two light chains (green and magenta). Each IgG molecule can be subdivided into an Fc and two Fab fragments through papain cleavage of the (hinge) region between these. At each end of a Fab fragment is a variable domain (VH/VL) involved in antigen binding. (B) Structure of an antibody VH (blue)/V(magenta) in complex with cognate antigen (grey). The antibody paratope (light green) and antigen epitope (light brown) are highlighted. (C) Structure of an antibody VH (blue)/V(magenta) highlighting the six hypervariable loops that make up the paratope; CDRH1 (white), CDRH2 (red), CDRH3 (amber), CDRL1 (green), CDRL2 (light blue), CDRL3 (yellow). (D) Comparison of antibody VH/VL domain (grey) and nanobody (red) structures. Nanobodies are devoid of the light chain, thus all the binding is mediated by theVH-homologous portion including its three CDR loops (CDRH13).

    Sequence Databases

    The International Immunogenetics Information System (IMGT) is the primary reference source for germline antibody sequences and is widely used for assigning gene segments in recombined antibodies [46]. Other platforms, such as Abysis

    [47] and DIGIT [48], typically store recombined variable region sequences (VH and VL), often obtained from repositories like the European Nucleotide Archive (ENA) [60] and the National Center for Biotechnology Information (NCBI) [61].

    Databases like DIGIT and Abysis typically contain around 10 sequences, including many from artificially engineered antibodies. These sequences are generally high-quality, originating from individual submissions using methods such as Sanger sequencing. In contrast, high-throughput repositories such as iReceptor [49] and Observed Antibody Space [17] aggregate large-scale datasets from NGS experiments, often encompassing more than 10 sequences.

    NGS-derived sequences can carry inherent error rates due to the scale and speed of data generation [62]. To mitigate this, databases like Observed Antibody Space provide annotations for predicted sequencing errors [62]. Additionally, these sequences often include metadata such as CDR region annotations, standardized numbering schemes, andwhen availabledetails about the immune state of the donor at the time of sampling.

    Most NGS repositories currently offer only unpaired heavy and light chains. However, advancements in paired sequencing technologies are expected to make paired chain datasets more readily accessible in the near future [63,64], which will further enhance computational modeling and therapeutic design capabilities. Structure Databases

    The Protein Data Bank (PDB) serves as the principal global repository for three-dimensional (3D) structural data of proteins [65]. Several specialized tools extract antibody- specific fragments or data from the PDB:

    • PyIgClassify categorizes CDR loops into canonical classes [51].

    • PCLICK gathers detailed antibodyantigen interaction data [50].

    • Full antibody structures are reachable via IMGT/3D- Structure-DB [66], SAbDab (Structural Antibody Database) [16], Abysis [47], and AbDb [52].

      As of now, approximately 3,500 structures in the PDB include at least one antibody or nanobody chain, out of a total of

      ~150,000 entries. SAbDab offers a downloadable weekly- updated dataset, ideal for modelling or docking projects. Meanwhile, Abysis and SAbDab enable structure retrieval by sequence queries or classification of CDR canonical forms. The Immune Epitope Database (IEDB) also integrates structural data with experimentally identified epitope information [18].

      Experimental Databases

      To extend structural and sequence insights, various databases provide experimental measurements relevant to antibody binding:

    • The IEDB includes epitope-specific antibody sequences linked to structural data [67].

    • Binding affinity details can be found in SAbDab and in the broader PDBBind database [54].

    • Targeted data such as mutation-driven changes in affinity are cataloged in Ab-Bind (covering 1,101 mutations in 32 antibody complexes) [19].

    • The SKEMPI database provides binding energy changes for diverse protein complexes, not limited to antibodies [55].

    mutations affecting antibody binding affinity

    SKEMPI

    SKEMPI

    Database for mutations influencing non- antibody protein interactions

    [55, 56]

    Non- redundant Nanobody

    Database

    Article

    Curated non- redundant structural database

    of nanobodies

    [57]

    SAbDab- Nano

    SAbDab- Nano

    Nanobody-specific extension of the SAbDab structure

    database

    [58]

    Institute of Analysis and Collection of

    Nanobodies

    IACN

    Database with nanobody sequences and structural models

    [59]

    Table 1. Databases containing information on antibody and nanobody structure and sequence. Most of the databases are free for academic use. In cases where the authors made it clear that a commercial version is available, this is indicated next to the database name. In some cases, such as IMGT or SKEMPI, conditions for non-commercial reuse are defined. In such cases, the authors of the respective databases should be contacted for details on commercial re-use of their material. Example contents of the databases are summarized in Supplementary Section 1. An up-to date list of antibody-related database resources is maintained at http://naturalantibody.com/tools

  3. Computational Approaches for Antibody Engineering

    Bioinformatics tools build upon the wealth of antibody data to support engineering endeavours throughout therapeutic development (see Table 2). Computational methods assist both during Lead Identificationwhere initial candidates are foundand Lead Optimizationwhere candidates are refined. These tools help evaluate binding strength, stability, immunogenicity, and other critical attributes before moving forward to clinical testing.

    Antibody Numbering

    A foundational step in computational antibody characterization is assigning sequence positions using standardized numbering frameworks (Table 2A). Nucleotide sequences of variable domains are first translated and aligned to germline gene references (e.g., via IgBLAST [68] or IMGT VQuest [69]), identifying V, D, and J gene usage. This alignment facilitates mapping residues into standardized numbering systemslike Kabat [152], Chothia [32], or IMGT [153]. Tools such as ANARCI [83], Abnum [82], and AbRSA [81] automate this process, enabling consistent ientification of framework and CDR regions essential for subsequent modeling and prediction.

    1. Antibody Annotation/Numbering Tools

      Tool Name

      Function

      Link

      Refer ence

      IgBLAST

      Processes raw antibody data

      https://www.ncbi.nlm.nih

      .gov/igblast/

      [68]

      IMGT V-

      Quest

      Raw data sequence processing

      http://www.imgt.org/IM GTindex/V-QUEST.php

      [69]

      MiXCR

      Analyzes immune sequencing data

      https://mixcr.readthedocs. io/en/master/

      [70]

      Immcanta tion

      Antibody repertoire data processing

      https://immcantation.read thedocs.io

      [71,

      72]

      IgReC

      Constructs immune repertoires

      https://yana- safonova.github.io/ig_rep ertoire_constructor/

      [73]

      ImmuneD

      Analyzes

      https://bitbucket.org/Imm

      [74]

      Database Name

      Link

      Description

      Reference

      TABS

      (commercial use)

      TABS

      Repository of approved therapeutic

      antibodies

      n/a

      SAbDab – therapeutic antibodies

      SAbDab

      Collection of therapeutic antibodies with

      structural data

      [13]

      PCLICK

      PCLICK

      Database of antibody-antigen

      binding clusters

      [50]

      Andrew Martins

      Antibody Resources

      Link

      Compilation of antibody-related

      bioinformatics tools and resources

      [43]

      AAAAA

      AAAAA

      Educational resources on antibody structures

      and engineering

      [43]

      AbMiner

      AbMiner

      Database providing monoclonal antibody data

      [44]

      Igpdb

      Igpdb

      Archive of inferred germline immunoglobulin variants

      [45]

      IMGT®

      IMGT

      Authoritative database for immunoglobulin

      gene sequences

      [46]

      Abysis (commercial license)

      Abysis

      Combines sequence and structure information of

      antibodies

      [47]

      DIGIT

      DIGIT

      Antibody sequence analysis tool

      [48]

      IReceptor

      IReceptor

      Platform for sharing and querying B-cell

      receptor NGS data

      [49]

      Observed Antibody Space

      OAS

      Repository of antibody and BCR sequences

      obtained via NGS

      [17]

      SystemsDB (commercial license)

      SystemsDB

      Repository for antibody and TCR sequence data from high- throughput

      sequencing

      n/a

      PyIgClassify

      PyIgClassify

      Canonical class database for CDR loop conformations

      [51]

      Structural Antibody

      Database (SAbDab)

      SAbDab

      Automatically updated

      antibody/nanobody structure database

      [16]

      AbDb

      AbDb

      Comprehensive database of antibody 3D

      structures

      [52]

      Immune Epitope Database

      IEDB

      Manually curated repository of immune epitope

      data

      [18]

      AntigenDB

      AntigenDB

      Resource for antigenic proteins

      [53]

      PDBBind

      PDBBind

      Protein-ligand binding affinity data from PDB

      [54]

      Ab-Bind

      Ab-Bind

      Database of

      [19]

      iversity

      immune repertoire diversity

      unediversity/ImmuneDiv ersity/

      IMSEQ

      Preprocesses immune sequencing data

      http://www.imtools.org/

      [75]

      Partis

      V(D)J

      inference and clonal clustering

      https://github.com/psathy rella/partis

      [76]

      IGOR

      Models B cell receptor generation

      https://github.com/mikem c/igor

      [77]

      Vidjil

      Immune

      repertoire visualization

      http://www.vidjil.org/

      [78,

      79]

      ImmuneD B

      Immune sequencing data analysis

      https://immunedb.readthe docs.io/en/latest/

      [80]

      AbRSA

      Numbering system for antibodies

      http://cao.labshare.cn/Ab RSA/

      [81]

      Abnum

      Antibody numbering

      resource

      http://www.bioinf.org.uk/ abs/abnum/

      [82]

      ANARCI

      Numbering scheme classification

      http://opig.stats.ox.ac.uk/ webapps/sabdab- sabpred/ANARCI.php

      [83]

      Tool

      Function

      Link

      Refer ence

      AbodyB uilder

      Comprehensi ve modeling of antibody

      variable regions

      http://opig.stats.ox.ac.uk/we bapps/sabdab- sabpred/Modelling.php

      [84]

      LYRA

      Modeling of full variable regions

      http://www.cbs.dtu.dk/servi ces/LYRA/index.php

      [85]

      PIGS

      Full variable

      region modeling

      https://cassandra.med.unito.i t/pigspro/

      [86]

      Kotai Antibod y Builder

      Complete variable region modeling

      http://kotaiab.org/

      [87]

      Rosetta Antibod y

      Rosetta- based full variable region

      modeling

      https://rosie.rosettacommon s.org/antibody

      [88,

      89]

      BIOVIA

      General modeling tool including antibody support

      https://www.3dsbiovia.com/

      [90]

      MoFvAb

      Full variable region modeling

      [91]

      WAM

      Antibody variable modeling

      [92]

      BioLumi nate

      Full variable region modeling via Schrödinger

      https://www.schrodinger.co m/products/bioluminate

      [93]

      MOE

      Modeling of antibody

      variable regions

      https://www.chemcomp.co m/

      [94]

      ABGEN

      Antibody modeling tool

      [95]

      AbPredi

      Rosetta-

      http://abpredict.weizmann.a

      [96]

    2. Structural Antibody Modelling Tools

      ct

      based modeling method

      c.il/bin/steps

      SmrToA ntibody

      Complete antibody modeling

      https://www.macromoltek.c om/

      [97]

      PEARS

      Predction of antibody side

      chains

      http://opig.stats.ox.ac.uk/we bapps/sabdab-

      sabpred/PEARS.php

      [98]

      H3Loop Pred

      Specific prediction of H3 loop

      [99]

      SCWRL

      Predicts side chain conformation

      s

      http://dunbrack.fccc.edu/sc wrl4/

      [100]

      BetaScp Web

      Predicts side chain placement

      http://voronoi.hanyang.ac.kr

      /betascpweb

      [101]

      SPHINX

      Ab initio loop prediction

      http://opig.stats.ox.ac.uk/we bapps/sabdab- sabpred/Sphinx.php

      [102]

      FREAD

      Database search-based loop

      modeling

      http://opig.stats.ox.ac.uk/we bapps/fread/php

      [103]

      PLOP

      Predicts antibody loop regions

      http://www.jacobsonlab.org/ plop_manual/plop_overview

      .htm

      [104]

      Chothia Canonic al

      Assigns loop structures based on

      Chothia rules

      http://www.bioinf.org.uk/ab s/chothia.html

      [105]

      SCALO P

      CDR

      classification

      and structure assignment

      http://opig.stats.ox.ac.uk/we bapps/sabdab- sabpred/SCALOP.php

      [106]

      Roche VH/VL

      orientati on

      Determines VH/VL

      orientation

      Part of Rosetta Suite

      [107]

      Rosetta VH/VL

      orientati

      on

      Models VH/VL

      orientation

      Part of Rosetta Suite

      [108]

      ABangle

      Defines VH/VL

      orientation angle

      http://opig.stats.ox.ac.uk/we bapps/abangle/index.html

      [109]

      Computational Tools for AntibodyAntigen Interaction Prediction and Design

    3. AntibodyAntigen Interface Prediction

      Tool/Pla tform

      Function

      Access Link

      Refer ence

      Antibod y i-Patch

      Predicts paratope regions

      http://opig.stats.ox.ac.u k/webapps/sabdab- sabpred/ABipatch.php

      [110]

      Paratom e

      Predicts paratope regions

      http://ofranservices.biu. ac.il/site/services/parato me/

      [111]

      ProABC

      Predicts paratope regions

      http://circe.med.unirom a1.it/proABC/

      [112]

      Parapred

      Predicts paratope regions

      https://github.com/elibe ris/parapred

      [113]

      Antibod yInterfac ePredicti

      on

      Predicts paratope regions

      https://github.com/seba stiananderlaku/Antibod yInterfacePrediction

      [114]

      AG- FAST-

      Parapred

      Paratope predictor

      [115]

      ISMBL AB-PPI

      Predicts protein contacts

      http://ismblab.genomics

      .sinica.edu.tw/predict-

      [3]

      ppi?pred=PPI

      Rapberg

      er et al. 2007

      Epitope prediction

      [116]

      PEASE

      Epitope prediction

      http://ofranservices.biu. ac.il/site/services/epitop e/index.html

      [117,

      118]

      PpiPred

      Epitope prediction

      http://opig.stats.ox.ac.u k/webapps/sabdab- sabpred/PpiPred.php

      [119]

      Jesperse n et al.

      Epitope prediction

      [120]

      EpiScore

      Epitope prediction

      [121]

      MabTop e

      Epitope prediction

      [122]

      ASEP

      Epitope prediction

      [123]

      BEPAR

      Epitope prediction

      [124]

      ABEPA R

      Epitope prediction

      [125]

      ClusPro

      Antibody docking

      https://cluspro.bu.edu/l ogin.php

      [8,

      126]

      Surfit

      Antibody docking

      https://sysimm.ifrec.osa ka-

      u.ac.jp/docking/main/

      [127]

      SnugDo ck

      Antibody docking

      http://rosie.graylab.jhu. edu/snug_dock

      [128]

      FRODO CK

      Antibody docking

      http://frodock.chaconla b.org/

      [129]

      DockSor ter

      Docking (not Ab- specific)

      http://www.stats.ox.ac. uk/~krawczyk/dockings upp.html

      [110]

      Hex

      Docking (not Ab- specific)

      http://hex.loria.fr/

      []

      ZDOCK

      Docking (not Ab- specific)

      https://zdock.umassmed

      .edu/

      [130]

      HADDO CK

      Docking (not Ab- specific)

      https://haddock.science.

      uu.nl/services/HADDO CK2.2/

      [131,

      132]

      ATTRA CT

      Docking (not Ab- specific)

      http://www.attract.ph.tu

      m.de/services/ATTRA CT/attract.html

      [133]

      GRAM M-X

      Docking (not Ab- specific)

      http://vakser.compbio.k u.edu/resources/gramm/ grammx/

      [134]

      pyDock Web (pyDock

      ,

      FTDock)

      Docking (not Ab- specific)

      https://life.bsc.es/pid/py dockweb

      [135]

      Swarmd ock

      Docking (not Ab- specific)

      https://bmm.crick.ac.uk

      /~svr6/swc-bmm- swarmdock

      [136]

      PatchDo ck

      Docking (not Ab- specific)

      https://bioinfo3d.cs.tau. ac.il/PatchDock/

      [137,

      138]

      Table E Antibody Design

      Tools for Humanization and Developability in Pharmaceutical Applications

      Tool/Pla tform

      Primary Use

      Access Link

      Cita tion

      Humane nss Score Evaluato

      r

      Humaniz ation

      http://www.bioinf.org.uk/abs/sha b/

      [14]

      Humaniz er

      Humaniz ation

      https://drive.google.com/file/d/1s eCQYMlMG4_oC1- 0EjDhZHMt9D-

      l8R5/view?usp=sharing

      [141

      ]

      Tabhu

      Humaniz ation

      http://circe.med.uniroma1.it/tabh u/

      [144

      ]

      Human

      String Content

      Humaniz ation

      Not available

      [145

      ]

      Human String Content (Alternat e)

      Humaniz ation

      Not available

      [145

      ]

      T20

      Score

      Humaniz ation

      https://dm.lakepharma.com/bioin formatics/

      [146

      ]

      codaH

      Humaniz ation

      Not available

      [147

      ]

      Develop ability Index

      Develop ability

      Not available

      [148

      ]

      Delayed eavy Chain Retentio n

      Predictor

      Develop ability

      Not available

      [149

      ]

      Therape utic Antibod y Profiling

      Tool

      Develop ability

      http://opig.stats.ox.ac.uk/webapp s/sabdab-sabpred/TAP.php

      [13]

      Lonza Tool

      Develop ability

      Not available

      [15]

      Tool/Pl atform

      Function

      Access Link

      Refer ence

      OPTCD R

      Design Protocol

      http://www.maranasgrou p.com/submission/OptC

      DR_2.htm

      [139]

      OPTMA VEN

      Design Protocol

      https://github.com/mara nasgroup/OptMAVEn_2

      .0

      [140,

      141]

      Rosetta Antibod yDesign

      Design Protocol

      https://www.rosettacom mons.org/docs/latest/app lication_documentation/

      antibody/RosettaAntibo dyDesign

      [142]

      AbDesig n

      Design Protocol

      https://www.rosettacom mons.org/node/9206

      [12,

      143]

    4. Antibody Design

      Antibody Modeling

      Antibody homology modelling generates 3D structures from amino acid sequences. Conservation across framework regions and canonical CDR loops makes these models highly reliable [7]. Typically, modeling involves:

      1. Template selection for heavy and light chains.

      2. VH-VL orientation alignment.

      3. CDR loop modeling, which is routine for canonical loops but complex for CDRH3 (necessitating ab initio methods or hybrid approaches like Sphinx [102]).

      4. Side-chain placement, refined by tools like SCWRL

        [100] or antibody-specific PEARS [98].

      5. Energetic refinement using platforms such as Rosetta [89].

    Antibody Modeling: Five-Step Process and Available Tools

    Antibody structure prediction typically involves a five-step pipeline (Figure 2A). The process begins with the selection of a suitable framework template, which serves as the structural base for grafting complementarity-determining regions (CDRs). This step usually involves identifying high sequence similarity in known antibody structures for both heavy (VH) and light (VL) chains using structural databases (16).

    The next critical step is determining the correct relative orientation between the VH and VL domains. This spatial relationship significantly influences the overall geometry of the paratope. Dedicated tools like AbAngle have been developed to calculate these orientations accurately (107, 109).

    Following orientation, the CDR loopsespecially the five canonical onesare modeled. Knowledge-based algorithms can predict these loop structures with high accuracy if suitable templates are available (103, 156). However, modeling the CDRH3 loop remains a significant challenge due to its high structural diversity (156). When no suitable template is available, ab initio approaches generate loop conformations from scratch. Although powerful, they are computationally intensive and often require further steps to select the best loop among numerous candidates (102). Hybrid strategies, such as Sphinx, integrate both knowledge-based and ab initio techniques, improving reliability in template-limited scenarios (102).

    Once the loop conformations are modeled, the fourth phase focuses on predicting and refining side-chain orientations. General-purpose side-chain modeling tools like SCWRL (100) are frequently used, but specialized methods like PEARS designed specifically for antibodiescan produce more accurate side-chain conformations (98).

    The final step involves energy minimization to refine the full antibody structure and improve atomic packing. This can be performed using tools like Rosetta (89), which optimize the models energetic landscape to yield a physically plausible conformation.

    Multiple software tools and platforms are available to implement these modeling strategies. Some of the freely accessible web servers include PIGS (86) and AbodyBuilder

    (84). Commercial packages offering antibody modeling functionalities include Biovia from Accelrys (3dsbiovia.com), SmrtMolAntibody from Macromoltek (macromoltek.com), MOE from Chemical Computing Group (chemcomp.com), and BioLuminate by Schrödinger Inc. (schrodinger.com). Tools like AbPredict (96) and Rosetta (89) are also available for local installation.

    These platforms differ significantly in computational efficiency. For instance, AbodyBuilder can generate a structural model in about one minute, whereas Rosetta-based frameworks may require several hours to complete a run. Nevertheless, the predictive accuracy across different tools tends to be comparable. In the Antibody Modeling Assessment II (AMA II) study (7), multiple software packages underwent blind benchmarking. The results revealed an average root mean square deviation (RMSD) of 1.1 Ã… for the predicted Fv regions, although modeling accuracy for the CDRH3 loop remained limited, sometimes exceeding 5 Ã… RMSD.

    While these computational models cannot fully match the resolution of experimental structural data, an RMSD of ~1.0 Ã… is sufficient to infer meaningful structural and functional insights. These models can be instrumental during the Lead Identification phase, such as in identifying paratope residues for mutagenesis (110), or during Lead Optimization, for evaluating developability features like paratope surface hydrophobicity (13), which require detailed structural information about the antibodyantigen interface (119).

    Popular modeling tools include AbodyBuilder [84], which quickly delivers models (~1 min), and more computationally intensive platforms such as Rosetta. Benchmarking in Antibody Modelling Assessment II shows that these tools achieve ~1.1 Ã… RMSD accuracy overall, although CDRH3 can deviate by over 5 Ã… [7].

  4. Paratope & Epitope Prediction and Antibody Docking

    Paratope prediction

    Identifying antigen-contacting residues (paratopes) is critical; about half the residues in CDR regions directly bind antigen surfaces [157159]. Computational toolsranging from statistical predictors like Antibody i-Patch [110] and Paratome [111]to machine learning models like proABC [112], AntibodyInterfacePrediction [114], and deep learning systems Parapred [113] and AG-Fast-Parapred [115]help highlight binding residues. These guides are key during optimization to pinpoint mutation targets.

    Epitope prediction

    Understanding the antigen-binding site (epitope) informs therapeutic targeting and patent strategy. While experimental mapping is definitive, computational alternatives exist. Linear epitope predictors rely on sequence patterns, but conformational predictorsparticularly those accounting for antibodyantigen contextoffer more accurate results. Antibody-specific tools (e.g., ASEP [123], EpiPred [119], MabTope [122], Jespersen et al. [120]) prioritize paratope- epitope pairs for improved precision (Table 2C).

    Figure 2.Computational antibody methods schematic. (A) Antibody modelling produces three dimensional coordinates from the sequence of an antibody. Framework templates are identified and the VH/VL domains can be oriented with respect to each other if the two regions originate from different molecules. CDRs are modeled into the framework followed by side-chain prediction and refinement of the entire structure by energy minimization. (B) Antibody interface prediction identifies the residues on the antibody (paratope) that are in contact with the antigen (epitope). This is a special case of molecular docking in which the antibody antigen docking aims to recapitulatethe complex between the antibody and the antigen. (C) Antibody design optimizes the binding of an antibody against an epitope of choice through a series of modelling, docking and energy minimization steps. In ab initio design, novel paratopes are generated computationally and their structural stability and binding propensity against the cognate epitope assessed by energy functions. Hotspot grafting involves transferring known interaction motifs from the antigen partner protein to an antibody template.

    (D) Antibodies need to be immunologically safe and have favorable biophysical properties in order to be administered to humans. Humanization involves modifying an animal-derived sequence to resemble one with a higher degree of human amino acid content without affecting its affinity and specificity. Develop ability-specific applications annotate regions on the surface that might lead to poor solubility or aggregation altogether. (E) Entire antibody repertoires can be used to draw information on the mechanics of the adaptive immune system. Identification of antigen-specific sequences post-vaccination can identify antibodies that could bestow passive immunity. The dynamic state of the repertoire can be analyzed to identify diseases in the organism. The diversity of antibodies can be harnessed to create surface display libraries recapitulating naturally evolved preferences and advantages.

    Docking

    Predicting antibodyantigen complexes uses protein docking techniques:

    • Global ab initio docking, as employed by ClusPro

      [8,126] and ZDOCK [130].

    • Information-driven docking (e.g., SnugDock [9,89], HADDOCK [131,132]), which incorporates CDR positions or experimental constraints.

    Docking involves sampling potential complex structures followed by ranking (e.g., ZRANK, FireDock, Dock-Sorter). Flexibility-aware tools like SwarmDock, HADDOCK, and SnugDock can model conformational changes, improving accuracy.

    HADDOCK supports the integration of experimental restraintsNMR, HDX, mutagenesisto refine docking predictions, even with minimal epitope guidance [178]. Performance continues to be evaluated in benchmarks like CAPRI [179].

  5. Ultimately, combining paratope/epitope predictions with docking offers a cost-effective

    route to understanding antigen recognition, guiding experimental design. Computational Approaches for Therapeutic Antibody Discovery

    Antibody Design and Modeling

    Antibody modelling and antigen-binding interface prediction tools play crucial roles in both the early and advanced phases of therapeutic antibody development. During lead identification, these tools can be employed to design new antibodies from scratch (ab initio), while in lead optimization, they help refine candidates for improved binding and efficacy (as illustrated in Figure 2C and summarized in Table 2D). If the structure of the target antigen is known, it opens opportunities to computationally develop novel antibodies against it [180]. Pioneering work by Lippow and colleagues demonstrated that an existing antibodyantigen complex structure can be computationally modified to enhance binding affinity [181]. Their method involved comprehensive in silico mutagenesis of complementarity-determining regions (CDRs), followed by binding affinity evaluation using the CHARMM force field [182]. Some of these engineered variants showed increased target affinity, proving that computational tools alone can support affinity maturation.

    Since then, several ab initio antibody design protocols have emerged, notably OptCDR [139], OptMAVEn [140],

    AbDesign [143], and RosettaAntibodyDesign [142]. These tools typically follow a four-step pipeline: CDR creation, structural modelling, docking with the antigen, and interaction energy evaluation. OptCDR and RosettaAntibodyDesign derive CDR conformations using databases of canonical structures and model the CDRH3 loop specifically. On the other hand, OptMAVEn and AbDesign adopt a modular approach, assembling antibodies through recombination-like processes akin to V(D)J rearrangement. The resulting constructs are optimized using established energy functions such as RosettaEnergy [183] or CHARMM [182]. These designs are then tested by docking simulations and scored based on binding energy between the antibody and antigen. Although still relatively new, these approaches have shown experimental validation in some cases. Their broader utility in industrial drug development settings, however, awaits further confirmation.

    These methods also enable refinement of CDRs to improve stability and affinity through targeted mutagenesis and energy optimization. A distinct strategy termed "hot-spot grafting," proposed by Liu and colleagues, involves transplanting key binding motifs from known protein complexes onto antibodies [11]. Another innovative method, "re-epitoping," developed by Ofran's team, uses existing antibodies to probe epitope complementarity and guides the design of focused display libraries [184], speeding up the identification of therapeutic leads.

    These computational methodologies not only streamline early- stage antibody discovery but also support lead optimization by evaluating properties like immunogenicity and developability.

    Immunogenicity Assessment

    A significant portion of therapeutic antibodies originate from animal immunization, particularly in mice. These non-human- derived antibodies often provoke immune responses in patients, leading to anti-drug antibodies (ADAs). To mitigate this, a process known as humanization is used, in which mouse- derived CDRs are inserted into human antibody frameworks or the frameworks themselves are engineered to resemble human sequences [185, 186]. Traditional humanization involves aligning the sequence with human germline genes to choose a

    suitable template. However, germline comparisons may not reflect the full diversity of human antibody repertoires.

    Computational humanization methods have evolved to address this limitation by comparing the candidate sequence to thousands of recombined human antibody sequences (see Figure 2D and Table 2E). One of the earliest tools, Tabhu, matches a query antibody sequence against a vast repertoire of human antibodies from databases like DIGIT [144]. While this approach considers antibody diversity, simple sequence alignment is often inadequate. More sophisticated, statistically driven methods have since been developed. For instance, the Humanness Score by Andrew Martin's group evaluates how closely a sequence resembles the human amino acid distribution [14]. This score serves as a global metric for humanness.

    Further refinement came with the Human String Content (HSC) score, developed by Lazar and colleagues. HSC assesses short peptide segments (e.g., 9-mers) to flag potentially immunogenic regions that diverge from human norms [145]. Both Humanness Score and HSC are based on sequence similarity but newer methods now consider positional residue dependencies, improving predictive accuracy [187, 188]. Though still sequence-based, some like HSC incorporate structural contact data to enhance predictions.

    Structural models can also aid in a process called "resurfacing," where exposed immunogenic residues are replaced to reduce immune recognition. Choi and colleagues effectively combined structure-based design with HSC scoring to create de- immunized antibodies [147].

    However, immune reactions to biologics can still occur even with fully humanized antibodies. Immunogenicity is multifactorialshaped not only by sequence but also by individual patient profiles and protein product quality (e.g., presence of aggregates or degradation products) [190, 191]. A key initial step in immunogenicity is the presentation of therapeutic peptide fragments by MHC class II molecules to T- cells.

    Several computational platforms have been designed to predict binding between peptide sequnces and MHC class I or II molecules. These tools often use machine learning, including neural networks, to estimate binding affinities of peptides to MHC [192, 193]. Public resources like the IEDB provide validated data and epitope prediction tools, making them essential for immunogenicity assessments [18].

    Predicted MHC-II binding peptides in therapeutic antibodies can serve as indicators of immunogenic potential and guide modifications early in development. Epivax Inc.'s immunogenicity scale is one such predictive metric used to evaluate and prioritize antibody candidates [194].

    Kumar and co-workers observed that immune epitopes often overlap with aggregation-prone regions (APRs), particularly near the CDRs [195, 196]. This connection implies a shared mechanism between aggregation and immune activation and opens the door for simultaneous optimization of antibody efficacy, solubility, and safety using structure-guided engineering.

  6. Antibody Modelling, Immunogenicity, and Biophysical Properties

    Antibody modelling and antigen-binding interface prediction tools play crucial roles in both the early and advanced phases

    of therapeutic antibody development. During lead identification, these tools can be employed to design new antibodies from scratch (ab initio), while in lead optimization, they help refine candidates for improved binding and efficacy (as illustrated in Figure 2C and summarized in Table 2D). If the structure of the target antigen is known, it opens opportunities to computationally develop novel antibodies against it [180]. Pioneering work by Lippow and colleagues demonstrated that an existing antibodyantigen complex structure can be computationally modified to enhance binding affinity [181]. Their method involved comprehensive in silico mutagenesis of complementarity-determining regions (CDRs), followed by binding affinity evaluation using the CHARMM force field [182]. Some of these engineered variants showed increased target affinity, proving that computational tools alone can support affinity maturation.

    Since then, several ab initio antibody design protocols have emerged, notably OptCDR [139], OptMAVEn [140],

    AbDesign [143], and RosettaAntibodyDesign [142]. These tools typically follow a four-step pipeline: CDR creation, structural modelling, docking with the antigen, and interaction energy evaluation. OptCDR and RosettaAntibodyDesign derive CDR conformations using databases of canonical structures and model the CDRH3 loop specifically. On the other hand, OptMAVEn and AbDesign adopt a modular approach, assembling antibodies through recombination-like processes akin to V(D)J rearrangement. The resulting constructs are optimized using established energy functions such as RosettaEnergy [183] or CHARMM [182]. These designs are then tested by docking simulations and scored based on binding energy between the antibody and antigen. Although still relatively new, these approaches have shown experimental validation in some cases. Their broader utility in industrial drug development settings, however, awaits further confirmation.

    These methods also enable refinement of CDRs to improve stability and affinity through targeted mutagenesis and energy optimization. A distinct strategy termed "hot-spot grafting," proposed by Liu and colleagues, involves transplanting key binding motifs from known protein complexes onto antibodies [11]. Another innovative method, "re-epitoping," developed by Ofran's team, uses existing antibodies to probe epitope complementarity and guides the design of focused display libraries [184], speeding up the identification of therapeutic leads.

    These computational methodologies not only streamline early- stage antibody discovery but also support lead optimization by evaluating properties like immunogenicity and developability.

    Immunogenicity Assessment

    A significant portion of therapeutic antibodies originate from animal immunization, particularly in mice. These non-human- derived antibodies often provoke immune responses in patients, leading to anti-drug antibodies (ADAs). To mitigate this, a process known as humanization is used, in which mouse- derived CDRs are inserted into human antibody frameworks or the frameworks themselves are engineered to resemble human sequences [185, 186]. Traditional humanization involves aligning the sequence with human germline genes to choose a suitable template. However, germline comparisons may not reflect the full diversity of human antibody repertoires.

    Computational humanization methods have evolved to address this limitation by comparing the candidate sequence to thousands of recombined human antibody sequences (see Figure 2D and Table 2E). One of the earliest tools, Tabhu, matches a query antibody sequence against a vast repertoire of human antibodies from databases like DIGIT [144]. While this approach considers antibody diversity, simple sequence alignment is often inadequate. More sophisticated, statistically driven methods have since been developed. For instance, the Humanness Score by Andrew Martin's group evaluates how closely a sequence resembles the human amino acid distribution [14]. This score serves as a global metric for humanness.

    Further refinement came with the Human String Content (HSC) score, developed by Lazar and colleagues. HSC assesses short peptide segments (e.g., 9-mers) to flag potentially immunogenic regions that diverge from human norms [145]. Both Humanness Score and HSC are based on sequence similarity but newer methods now consider positional residue dependencies, improving predictive accuracy [187, 188]. Though still sequence-based, some like HSC incorporate structural contact data to enhance predictions.

    Structural models can also aid in a process called "resurfacing," where exposed immunogenic residues are replaced to reduce immune recognition. Choi and colleagues effectively combined structure-based design with HSC scoring to create de- immunized antibodies [147].

    However, immune reactions to biologics can still occur even with fully humanized antibodies. Immunogenicity is multifactorialshaped not only by sequence but also by individual patient profiles and protein product quality (e.g., presence of aggregates or degradation products) [190, 191]. A key initial step in immunogenicity is the presentation of therapeutic peptide fragments by MHC class II molecules to T- cells.

    Several computational platforms have been designed to predict binding between peptide sequences and MHC class I or II molecules. These tools often use machine learning, including neural networks, to estimate binding affinities of peptides to MHC [192, 193]. Public resources like the IEDB provide validated data and epitope prediction tools, making them essential for immunogenicity assessments [18].

    Predicted MHC-II binding peptides in therapeutic antibodies can serve as indicators of immunogenic potential and guide modifications early in development. Epivax Inc.'s immunogenicity scale is one such predictive metric used to evaluate and prioritize antibody candidates [194].

    Kumar and co-workers observed that immune epitopes often overlap with aggregation-prone regions (APRs), particularly near the CDRs [195, 196]. This connection implies a shared mechanism between aggregation and immune activation and opens the door for simultaneous optimization of antibody efficacy, solubility, and safety using structure-guided engineering.

    Despite these advancements, the relationship between computational epitope predictions and real-world ADA generation remains under investigation. Consequently, while computational de-immunization holds promise for more efficient therapeutic development, its clinical impact is yet to be fully validated.

    Biophysical Properties

    In addition to immunogenicity, the successful development of antibody therapeutics also depends on their biophysical characteristics. Key attributes include colloidal stability, viscosity at high oncentrations, and chemical or physical degradation profiles [197201]. Maintaining good solubility is especially critical [202, 203] to prevent aggregation, which can lead to decreased efficacy, antibody breakdown, or unwanted immune responses.

    Protein aggregation, a persistent issue in biopharmaceuticals, has both mechanistic and kinetic dimensions. Mechanistically, it involves identifying unstable regions in proteins, particularly aggregation-prone regions (APRs) characterized by surface- exposed hydrophobic patches. Various algorithms have been evaluated for their ability to predict APRs (Figure 2D, Table 2E) [204, 205]. Wang and colleagues demonstrated that marketed monoclonal antibodies (mAbs) often harbor multiple APR motifs in their CDRs [206]. These motifs not only contribute to antigen binding [160] but also explain how aggregation might reduce antibody potency and suggest targets for selective disruption to maintain activity.

    Recently, Rawat et al. collected experimental kinetic data on aggregation and applied machine learning to identify mutations that either promote or reduce aggregation rates in proteins [207]. While several general-purpose tools exist for predicting solubility and APRs [208, 209], specialized antibody-focused tools have also been developed [204, 210]. For example, Lauer and collaborators assessed biophysical parameters of 12 antibodies over two years [148], deriving a Developability Index (DI). This score integrates calculated hydrophobicity, surface aggregation propensity (SAP) [211], and net molecular charge to assess aggregation risk.

    Identifying hydrophobic surfacesa key factor in aggregation riskideally requires crystal structures or accurate homology models. Jain and team addressed this by developing a surface accessibility predictor that generates a risk score based on sequence data [149]. Metrics like DI and aggregation propensity leverage hydrophobicity and charge annotations, indicating these alone can provide useful developability insights. Obrezanova et al. expanded this by creating an Adaptive Boosting model using a wide range of physicochemical features to predict aggregation tendencies [15], trained on a dataset of 500 antibody sequences.

    These approaches, often relying on proprietary clinical-stage data, enable early candidate filtering for favorable developability. Alternatively, naturally occurring antibody sequences can serve as a proxy for desirable properties [13]. Raybould and colleagues proposed five guidelines based on such sequences. One of these involves comparing structure- based hydrophobicity scores against a large dataset of natural antibodies derived from next-generation sequencing (NGS). Deviations from the natural distribution indicate potential developability risks. This method exemplifies the innovative use of large-scale NGS data in guiding therapeutic antibody design and optimization.

  7. Emerging Trends: Leveraging NGS Data for Antibody Engineering

    The advancement of computational strategies for antibody design is increasingly dependent on the integration of next- generation sequencing (NGS) data. This data, particularly from B-cell receptor (BCR) sequencing, is being used as a proxy for antibody repertoire analysis [212, 213]. Numerous online repositories now offer access to NGS datasets [17], which have proven valuable in evaluating therapeutic antibodies [13]. Current bioinformatic efforts primarily focus on interpreting immune repertoire diversity, with several potential applications in therapeutic development [22, 25, 214].

    A major use of computational analysis of NGS data involves identifying antigen-specific BCR sequences post-immunization (Figure 2E). When an antigen is introduced, it stimulates the production of specific antibodies, leading to a skewed immune profile. By sequencing the immune repertoire and clustering similar sequencesparticularly those sharing V and J genes and CDRH3 regionsresearchers can identify candidate antigen-specific antibodies. This technique has been applied to human vaccination studies, such as with Hepatitis B [215], and in mouse models [216]. However, these basic clustering methods can sometimes fail to detect low-abundance antigen- specific sequences or may mistakenly identify unrelated sequences as relevant [215]. More sophisticated statistical models, as demonstrated by Fowler et al., improve accuracy by reducing false positives [217]. Identifying such antibodies is particularly useful in vaccine development, as they can serve as candidates for passive immunization [218].

    Beyond antigen recognition, NGS analysis can also help infer an individual's immune status (Figure 2E). Since the immune repertoire reflects overall health, certain antibody signatures may correlate with disease states [219]. For example, classifiers have been trained to differentiate immune profiles linked to chronic lymphocytic leukemia [220], multiple sclerosis [221], and influenza [222]. Expanding these models could eventually lead to diagnostic tools capable of detecting numerous conditions solely through BCR sequencing.

    Improving detection of antigen-specific sequences may require a deeper understanding of the sequence and structural principles that govern immune responses. Despite the immense diversity in antibody sequences, recent research has shown that certain sequence motifs are frequently shared across individuals [23, 223]. Even after discarding a majority of sequences (5090%), key diversity features persist in the human antibody repertoire [214]. Moreover, structural constraintsparticularly in the variable CDRH3 region appear consistent among individuals [224]. Notably, many therapeutic CDRH3 loops are also found in natural repertoires from NGS studies, suggesting convergence between natural immunity and therapeutic design [225].

    Recognizing these evolutionary patterns can inform the creation of more effective antibody libraries. For instance, an analysis of antibodies from over 600 donors [24] was used to guide the development of libraries based on naturally preferred sequence positions [26]. Libraries built on this foundation may yield antibodies with superior biophysical and immunological profiles.

    Continued progress in NGS-based antibody engineering will depend not only on algorithmic innovation but also on data quality. Most current NGS datasets lack paired heavy and light chain information. Advancements in single-cell sequencing technology are crucial for generating such paired datasets [64, 227], which will significantly enhance computational exploration of the immune system and improve the development of next-generation antibody therapeutics.

    Alternative Antibody Formats: Nanobodies

    Recent advancements in antibody therapeutics have extended beyond traditional IgG molecules to include alternative molecular formats, particularly nanobodies. These are heavy- chain-only antibodies that naturally occur in camelids such as camels, alpacas, and llamas [27], as well as in certain species of sharks [228, 229]. Interest in nanobodies has grown substantially, especially following the approval of caplacizumab in 2018the first therapeutic nanobody. This increasing attention has also led to the creation of specialized databases and analytical tools dedicated to nanobody sequences and structures [57, 58, 231, 232].

    Nanobodies consist of a single variable domain containing three highly diverse loops: CDRH1, CDRH2, and CDRH3. These loops form a compact and elongated paratope on one side of the folded domain. The absence of a light chain results in significant differences between nanobodies and conventional antibodies in terms of both sequence composition and structural conformation. This allows nanobodies to recognize epitopes that are inaccessible to full-length antibodies, such as those buried within enzyme active sites, viral structures, or G protein-coupled receptors [233, 234].

    Large-scale computational comparisons between classical antibodies and nanobodies reveal substantial systemati distinctions [231, 232]. Nanobodies show less variation in their framework regions but exhibit similar sequence diversity in the CDRH1 and CDRH2 loops when compared to traditional antibodies [232]. Notably, even with similar sequence diversity, nanobodies display greater structural variation in these regions. Unlike classical antibodies, the CDRH1 and CDRH2 loops in nanobodies do not conform to established canonical structural rules, presenting significant challenges for computational modelling [232, 235].

    Additionally, nanobody CDRH3 loops tend to be three to four residues longer than those in conventional antibodies and exhibit greater diversity in both sequence and 3D structure [230, 232, 235, 236]. This variability contributes to unique loop conformations, such as extended finger-like projections, which enable deep insertion into antigen binding pockets.

    From a modelling perspective, nanobody paratopes present even more complexity. On average, they include nearly three additional amino acid residues compared to those found in

    standard antibody VH domains. Moreover, nanobody paratopes draw from a broader array of sequence positions, roughly equivalent to the combined VH-VL interface seen in conventional antibodies [230, 232]. Since the VL domain in classical antibodies contributes relatively little structural variability, this expanded footprint in nanobodies implies a greater need for refined modelling tools.

    Further complicating matters, structural analyses of nanobody antigen complexes reveal that nanobody paratopes consist of a more diverse array of structural motifs compared to classical antibodies [231]. The highly variable CDRH3 loop is often the primary contributor to antigen interaction, reinforcing the notion that nanobodyantigen interfaces cannot be easily modeled using traditional tools developed for IgG antibodies.

    Given these fundamental differences, it is currently uncertain whether existing computational approaches for antibody modelling, docking, and affinity prediction are directly applicable to nanobodies. To clarify this, a comprehensive benchmarking of current antibody modelling tools against nanobody datasets is essential. Such an evaluation would highlight limitations and guide the development of new methods tailored specifically to the unique structural and functional characteristics of nanobodies.

    Acknowledgement:

    This work was supported by the Department of Bioengineering, Integral University, Lucknow, thankfully acknowledges the support provided by the Head of Department Prof. Alvina Farooqui, Faculty of engineering.

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