Antibody–antigen docking

What is antibody–antigen docking?

Antibody–antigen docking is a computational method for arranging an antibody variable region and its antigen into plausible bound orientations. Antibody-specific paratope information and experimental epitope evidence can narrow an otherwise difficult macromolecular search.

Antibody–antigen docking is a protein–protein docking problem with a constrained antibody paratope and a sometimes unknown antigen epitope. Framework regions are often modeled confidently, but uncertainty in the complementarity-determining regions, especially CDR H3, can change the proposed interface orientation and contacts.

The search may be global or restrained by paratope predictions, peptide mapping, escape mutations, competition experiments, cross-links, or known antigenic regions. Preparation must preserve the correct heavy and light chains and account for unresolved loops, engineered residues, and glycans near the interface.

When to use antibody–antigen docking

• Suitable antibody–antigen docking question. Generating epitope, paratope, and binding-orientation hypotheses
• Required structures and evidence are available. Quality antibody and antigen structures or models, with epitope or paratope evidence where available

Benefits of antibody–antigen docking

• Practical output. Uses antibody-specific structural context
• Comparative evidence. Can incorporate interface restraints
• Connected analysis. Creates testable residue-level hypotheses

Primary limitations

• Method dependence. CDR flexibility is challenging
• Input sensitivity. Glycans and missing loops affect interfaces
• Validation boundary. Unrestrained global searches produce many false positives

How antibody–antigen docking works

Useful antibody–antigen protocols combine antibody-specific structural evidence with macromolecular docking.

• Global antibody–antigen search. Global sampling explores the antigen surface when the epitope is unknown. It is useful for hypothesis generation but produces a large number of false-positive orientations.
• Paratope- or epitope-restrained docking. Predicted or experimental interface residues guide HADDOCK3 or related methods toward biologically plausible contacts. Incorrect restraints can exclude the true orientation.
• Learned complex prediction. Co-folding and diffusion models provide complementary complexes, but antibody-loop uncertainty and training-set similarity must be examined rather than hidden behind one confidence score.

Applications of antibody–antigen docking

Antibody–antigen docking is most useful when it converts sequence, structural, or experimental mapping evidence into testable interface models.

• Epitope hypothesis generation. Identify candidate antigen residues that may explain binding, competition, or escape behavior.
• Paratope interpretation. Relate CDR residues to predicted antigen contacts and prioritize positions for affinity maturation or specificity testing.
• Complex-model preparation. Build starting structures for geometric review, mutational planning, or comparison with low-resolution experimental data.

How to do antibody–antigen docking online

ProteinIQ provides connected antibody modeling, paratope prediction, and complementary docking tools so every assumption can be reviewed.

1. Prepare the antibody structure. Upload a variable-region structure or build one from correctly paired heavy- and light-chain sequences. Inspect CDR loops and engineered residues before docking.
2. Prepare the antigen. Choose the relevant antigen construct, chains, oligomeric state, and glycans. Repair missing atoms and note unresolved regions near candidate epitopes.
3. Add paratope or epitope evidence. Use ParaSurf predictions or experimental mapping to define possible interface residues, and keep the confidence and source of each restraint explicit.
4. Run complementary docking. Compare HADDOCK3 and LightDock from the same structures. Use restrained and global modes as separate analyses when the evidence is uncertain.
5. Review interface models. Inspect CDR participation, antigen contacts, clashes, buried polar groups, glycan conflicts, and agreement with escape or competition data before exporting complexes.

How to interpret antibody–antigen docking results

A credible model should place plausible CDR residues at the interface, avoid severe framework or glycan clashes, and explain independent epitope evidence. A high docking rank without antibody-specific support is weak evidence.

Docking cannot establish affinity, specificity, neutralization, cross-reactivity, or developability. Validate candidate epitope and paratope residues with binding measurements, mutagenesis, competition, escape profiling, or experimental complex structures.

How the antibody–antigen docking workflow works

Compare HADDOCK3 and LightDock orientations from the same antibody and antigen structures without requiring a native reference.

1. Model and inspect the antibody. Upload a variable-region structure or build one from correctly paired heavy- and light-chain sequences. Inspect CDR loops and engineered residues before docking.
2. Prepare the antigen. Choose the relevant antigen construct, chains, oligomeric state, and glycans. Repair missing atoms and note unresolved regions near candidate epitopes.
3. Map paratope or epitope evidence. Use ParaSurf predictions or experimental mapping to define possible interface residues, and keep the confidence and source of each restraint explicit.
4. Dock complementary searches. Compare HADDOCK3 and LightDock from the same structures. Use restrained and global modes as separate analyses when the evidence is uncertain.
5. Review interfaces. Inspect CDR participation, antigen contacts, clashes, buried polar groups, glycan conflicts, and agreement with escape or competition data before exporting complexes.

Inputs and outputs

Check formats before running, then inspect and download the result from every workflow step.

Inputs

• Structural inputs. PDB SDF SMILES Antibody variable-region and antigen PDB structures, optionally with epitope or paratope residue evidence.
• Method context. Binding-site evidence, restraints, receptor-state provenance, known ligands, or reference complexes when available.

Outputs

• Docked structures. PDB PDBQT SDF Candidate complexes, interface contacts, method scores, and reference-based DockQ results when a native structure is available.
• Review evidence. Method-native rankings, confidence, logs, interaction context, failures, and files for reproducible follow-up.