Homology modeling

What is homology modeling?

Homology modeling, also called comparative modeling, is a method for building a target protein structure from one or more related proteins with experimentally determined structures. It aligns the target sequence to those templates and transfers their structural framework, so model reliability depends strongly on template choice, sequence alignment, and treatment of insertions, loops, and side chains.

A genuine homology-modeling workflow starts with template search, ranks candidate templates by relationship and experimental quality, builds a target–template alignment, constructs the model, and evaluates the result. A high global sequence identity can still hide alignment errors around active sites, indels, domain boundaries, and long loops.

ProteinIQ does not currently run a dedicated comparative-model builder. The runnable workflow on this page begins with a model produced by a specialist service or local package, then keeps repair, stereochemical validation, and reference comparison connected without claiming that those downstream tools generated the model.

When to use homology modeling

• Suitable homology modeling question. Targets with a structurally characterized relative and a credible target–template alignment
• Inputs and evidence are available. Target sequence, selected template structures, alignment, and an external comparative-model output
• A validation plan is in place. Retain the template structures, target–template alignment, model-building program, and settings. A clean geometry report does not establish that template choice or alignment was correct.

Benefits of homology modeling

• Makes template-derived assumptions explicit.
• Can preserve family-specific structural detail.
• Supports residue-level comparison with known structures.

Primary limitations

• ProteinIQ does not yet build the comparative model itself.
• Alignment errors propagate directly into coordinates.
• Low-identity loops and insertions remain uncertain.

Homology modeling methods and interpretation

Template selection should consider biological assembly, domain coverage, ligands, mutations, resolution, and conformational state—not sequence identity alone. The alignment must preserve structurally equivalent residues and deserves manual inspection near functional regions.

Validation cannot prove that a model is correct, but it can identify implausible local geometry and quantify similarity to a chosen reference. Keep template identity, alignment, modeling settings, and any subsequent coordinate repair with the exported record.

How to run homology modeling online

The ProteinIQ workflow keeps the inputs, actual tool runs, method-native files, and comparison outputs together. Follow these steps while preserving the scientific boundary described above.

1. Select templates. Search for structurally characterized homologs and select templates outside ProteinIQ.
2. Review the alignment. Review the target–template alignment, especially gaps, domain junctions, and functional residues.
3. Build the model externally. Generate the comparative model with a dedicated homology-modeling service or package.
4. Check geometry and clashes. Import the PDB into the ProteinIQ workflow and run PDBFixer, MolProbity, and Ramachandran Plot.
5. Compare with structural evidence. Use US-align against a relevant reference and export the model with its provenance and validation results.

How homology modeling works

Import an external comparative model, repair common coordinate issues, inspect geometry, and compare it with a selected reference structure.

1. Select templates. Search for structurally characterized homologs and select templates outside ProteinIQ.
2. Review the alignment. Review the target–template alignment, especially gaps, domain junctions, and functional residues.
3. Build the model externally. Generate the comparative model with a dedicated homology-modeling service or package.
4. Check geometry and clashes. Import the PDB into the ProteinIQ workflow and run PDBFixer, MolProbity, and Ramachandran Plot.
5. Compare with structural evidence. Use US-align against a relevant reference and export the model with its provenance and validation results.

Inputs and outputs

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

Inputs

• Research input. FASTA PDB mmCIF An externally generated homology model in PDB format and, when available, a relevant experimental reference structure.

Outputs

• Prediction and review outputs. PDB mmCIF CSV JSON A repaired model, MolProbity and Ramachandran geometry results, plus US-align structural comparison metrics.