Protein Structure Prediction and Analysis

End-to-end workflow for protein structure prediction starting from a sequence or UniProt accession. Combines ESMFold de novo prediction, AlphaFold database retrieval, experimental structure benchmarking from RCSB, ProtVar variant impact assessment, and ProtParam sequence property calculation.

KEY PRINCIPLES:

1. Sequence first — obtain or verify the protein sequence before prediction
2. ESMFold for fast de novo — works directly on sequence (up to ~800 residues); no database lookup needed
3. AlphaFold for reference — retrieve precomputed AlphaFold model for comparison; use qualifier parameter (UniProt accession)
4. Quality before interpretation — always report pLDDT scores; do not interpret low-confidence regions as folded
5. Experimental validation — compare predictions to RCSB experimental structures when available
6. ProtVar for variants — use when the question involves mutations or SNVs affecting structure
7. English-first queries — use English protein names in all tool calls; respond in the user's language

LOOK UP, DON'T GUESS

When uncertain about any scientific fact, SEARCH databases first rather than reasoning from memory. A database-verified answer is always more reliable than a guess.

COMPUTE, DON'T DESCRIBE

When analysis requires computation (statistics, data processing, scoring, enrichment), write and run Python code via Bash. Don't describe what you would do — execute it and report actual results. Use ToolUniverse tools to retrieve data, then Python (pandas, scipy, statsmodels, matplotlib) to analyze it.

When to Use

Apply when users ask:

• "Predict the structure of this sequence: FASTA]"
• "What does the AlphaFold model for protein] look like?"
• "How confident is the AlphaFold prediction for protein]?"
• "Is there an experimental structure for protein] and how does it compare to AlphaFold?"
• "How does mutation variant] affect the structure of protein]?"
• "What are the physicochemical properties of protein] sequence?"
• "Predict the structure of this novel protein" / "I have a new sequence, can you model it?"

Not for (use tooluniverse-protein-structure-retrieval instead): retrieval-only tasks where user provides a PDB ID or wants to browse experimental structures without prediction.

Input Parameters

| Parameter | Required | Description | Example | |-----------|----------|-------------|---------| | sequence | Yes (for ESMFold) | Amino acid sequence (single-letter FASTA) | MVLSPADKTNVK... | | uniprot_id | Yes (for AlphaFold) | UniProt accession | P04637, P69905 | | variant | No | Variant notation for structural impact | P04637 R175H, TP53 R175H | | max_length | No | ESMFold limit: ~800 residues recommended | — |

Workflow Overview

Phase 0: Input preparation (sequence retrieval if needed)
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Phase 1: Sequence properties (ProtParam_calculate)
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Phase 2: De novo prediction (ESMFold_predict_structure)
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Phase 3: AlphaFold reference (alphafold_get_prediction + alphafold_get_summary)
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Phase 4: Experimental structure comparison (RCSBAdvSearch_search_structures, RCSBData_get_entry)
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Phase 5: Variant structural impact (ProtVar_map_variant + ProtVar_get_function) [if variant provided]
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Phase 6: Quality synthesis and interpretation

Phase 0: Input Preparation

Objective: Obtain or verify the protein sequence needed for ESMFold prediction.

If sequence is already provided

Use it directly for ESMFold_predict_structure. Check length:

• 1-400 residues: full prediction, high confidence expected
• 400-800 residues: prediction supported, may be slower
• >800 residues: ESMFold may fail or produce lower quality; recommend using AlphaFold instead

If only protein name or UniProt ID is provided

Retrieve sequence from UniProt_get_entry_by_accession:

• accession: UniProt accession
• Extract the sequence.value field from the response

Note: If only a name is given (not accession), first resolve with UniProt_search or MyGene_query_genes to get the UniProt accession, then fetch the sequence.

Phase 1: Sequence Properties

Objective: Calculate physicochemical properties before prediction to contextualize results.

Tools

ProtParam_calculate:

• sequence: amino acid sequence string (single-letter code)
• Returns: molecular weight, isoelectric point (pI), extinction coefficient, instability index, GRAVY score, amino acid composition

Key Properties to Report

• Molecular weight — size context
• Isoelectric point (pI) — charge at neutral pH
• Instability index — >40 suggests unstable protein; affects prediction quality
• GRAVY score — hydrophobicity; >0 indicates membrane association tendency
• Length — determines ESMFold feasibility

Phase 2: De Novo Structure Prediction (ESMFold)

Objective: Predict 3D structure from sequence using Meta's ESM-2 language model.

Tools

ESMFold_predict_structure:

• sequence: amino acid sequence string
• Returns: predicted structure in PDB format, per-residue pLDDT confidence scores, pTM score (global fold confidence)

Workflow

1. Call ESMFold_predict_structure with the sequence
2. Parse pLDDT scores:

• Per-residue confidence array
• Compute mean pLDDT over all residues
• Identify low-confidence regions (pLDDT < 50)

1. Parse pTM score (predicted Template Modeling score) — overall fold quality
2. Record the PDB-format coordinate output for downstream visualization

Quality Interpretation

| pLDDT Range | Interpretation | Reliability | |-------------|---------------|-------------| | >90 | Very high confidence | Equivalent to experimental quality | | 70-90 | High confidence | Backbone reliable, side chains approximate | | 50-70 | Low confidence | Potentially disordered or flexible region | | <50 | Very low confidence | Likely intrinsically disordered; do not interpret |

| pTM Score | Fold Confidence | |-----------|----------------| | >0.8 | High confidence global fold | | 0.5-0.8 | Moderate; some domains may be uncertain | | <0.5 | Low global fold confidence |

ESMFold vs AlphaFold

• ESMFold: faster, works directly on sequence, good for novel sequences, no database lookup
• AlphaFold: uses multiple sequence alignment (MSA); typically higher accuracy for well-conserved proteins
• Both predict single-chain monomer structures (not complexes in standard mode)

Phase 3: AlphaFold Reference Model

Objective: Retrieve precomputed AlphaFold2 model for comparison and higher-accuracy reference.

Tools

alphafold_get_prediction:

• qualifier (or alias uniprot_id / uniprot_accession): UniProt accession (e.g., "P04637")
• Returns: AlphaFold model URL, pLDDT scores, model version

alphafold_get_summary:

• qualifier (or alias uniprot_id / uniprot_accession): UniProt accession
• Returns: prediction summary including confidence metrics, model quality

alphafold_get_annotations (optional):

• qualifier: UniProt accession
• Returns: functional region annotations overlaid on structure (binding sites, active sites)

AlphaFill_get_transplants (optional, ligands/cofactors):

• uniprot: UniProt accession (e.g., "P00520" ABL1)
• Returns: ligands, cofactors, and ions transplanted onto the AlphaFold model by homology, with per-transplant local RMSD and source PDB IDs
• When to use it: the apo AlphaFold model omits bound ligands/metals; run this to recover the likely cofactor/ligand/ion environment (e.g., ABL1 → STI/imatinib) for structure-guided binding-site interpretation

Workflow

1. Call alphafold_get_prediction and alphafold_get_summary
2. Extract mean pLDDT and per-residue confidence
3. Compare ESMFold vs AlphaFold pLDDT profiles:

• Do they agree on low-confidence regions?
• Large differences may indicate disordered/flexible regions

1. Note the AlphaFold model version (v1/v2/v3/v4)

Decision Logic

• If no UniProt accession available: skip AlphaFold; use ESMFold only
• If protein is a complex or has multiple chains: note that both tools predict single chains
• If AlphaFold confidence is very high (mean pLDDT > 85): recommend using AlphaFold as primary reference

Phase 4: Experimental Structure Comparison

Objective: Check whether experimental structures exist in PDB and how predictions compare.

Tools

RCSBAdvSearch_search_structures (search by protein/gene name):

• query: protein name or gene symbol
• limit: number of results (default 10)
• Returns: list of PDB entries with resolution, method, title

RCSBData_get_entry (details for a specific PDB ID):

• pdb_id: 4-character PDB identifier
• Returns: metadata including method, resolution, chains, ligands, release date

Workflow

1. Search for experimental structures using protein name
2. Filter for highest-resolution X-ray or cryo-EM structures
3. For the best experimental structure, retrieve entry details
4. Compare to predictions:

• If experimental structure exists: note coverage, resolution, method
• Flag regions predicted with high confidence but missing from experimental structure (could be disordered in crystal)
• Flag regions in experimental structure with low pLDDT (may be crystal artifacts vs true fold)

Fallback

• If RCSB search returns no results: note "no experimental structure found in PDB" and proceed with predictions only
• Suggest checking PDBe as secondary source

Phase 5: Variant Structural Impact (When Variant Provided)

Objective: Assess how a specific amino acid substitution affects the predicted structure.

Tools

ProtVar_map_variant:

• variant: string notation like "P04637 R175H" or HGVS notation
• Returns: mapped residue position, genomic coordinates, consequence type, variant accession

ProtVar_get_function:

• accession: UniProt accession
• position: integer residue position
• variant_aa: mutant amino acid (single letter)
• Returns: functional annotations — domain, active site, binding site, conservation score, clinical significance, predicted pathogenicity

Workflow

1. Call ProtVar_map_variant to resolve the variant and confirm position
2. Call ProtVar_get_function with wild-type position to get domain context
3. Assess: is the mutated residue in a critical structural region?

• Active site / binding site: likely high functional impact
• Buried hydrophobic core: likely destabilizes fold
• Surface-exposed, disordered region: less likely to affect overall fold

1. Compare pLDDT at that position (from ESMFold/AlphaFold) to assess if the region is well-predicted

Evidence Grading for Variant Impact

| Tier | Evidence | |------|----------| | T1 | Clinical/functional data for this exact variant (from ProtVar) | | T2 | Variant at experimentally characterized active site or binding interface | | T3 | Computational pathogenicity prediction (PolyPhen, SIFT from ProtVar) | | T4 | Position in predicted structured region only |

Phase 6: Quality Synthesis and Report

Required Report Sections

1. Protein summary — name, length, pI, stability index (from ProtParam)
2. Structure prediction summary table:

| Method | Mean pLDDT | pTM/Global Score | Coverage | Notes | |--------|-----------|------------------|----------|-------| | ESMFold | X.X | X.X | 100% (full seq) | — | | AlphaFold | X.X | — | 100% | version vN | | Experimental (best) | N/A | N/A | XX% | PDB: XXXX, Xray, X.X A |

1. Confidence map — regions of high vs low confidence; highlight disordered regions
2. Experimental structure comparison — does PDB have coverage? How does prediction align?
3. Variant impact (if applicable) — domain context, pathogenicity, structural consequence
4. Recommendations:

• Which model to use for downstream applications (docking, design, etc.)
• Regions to treat as unreliable
• Suggested experimental validation approaches

Quality Minimums

• Report mean pLDDT for both ESMFold and AlphaFold
• Identify all low-confidence regions (pLDDT < 50) by residue range
• Check PDB for experimental structures (at minimum 1 search query)
• Compare at least 2 prediction sources when UniProt accession is available

Tool Parameter Reference

| Tool | Key Parameter | Notes | |------|--------------|-------| | ESMFold_predict_structure | sequence | Raw amino acid string, no spaces, no FASTA header | | alphafold_get_prediction | qualifier or uniprot_id | UniProt accession (e.g., "P04637") | | alphafold_get_summary | qualifier or uniprot_id | Same UniProt accession | | ProtParam_calculate | sequence | Same sequence string | | ProtVar_map_variant | variant | Format: "<UniProt_ID> <AA><pos><AA>" e.g., "P04637 R175H" | | ProtVar_get_function | position | Integer residue number |

Fallback Strategies

| Situation | Fallback | |-----------|----------| | ESMFold fails (sequence too long > 800 aa) | Use AlphaFold model only; note length limitation | | AlphaFold no entry for UniProt ID | Use ESMFold prediction only | | RCSB search returns no results | Note no experimental structure; proceed with predictions | | No UniProt accession available | Use ESMFold from raw sequence; skip AlphaFold | | ProtVar variant not found | Manually assess position from domain annotation in Phase 4 |

Databases Integrated

| Database | Coverage | What it provides | |----------|----------|-----------------| | ESMFold | Any protein sequence (up to ~800 aa) | De novo structure prediction from sequence alone | | AlphaFold DB | UniProt reviewed proteins (>200M entries) | Precomputed predictions with per-residue pLDDT | | RCSB PDB | ~220,000 experimental structures | Ground-truth experimental coordinates for comparison | | ProtVar | All UniProt proteins | Variant impact, domain context, clinical annotations | | ProtParam | Any sequence | Physicochemical sequence properties |

Limitations

• ESMFold length limit: sequences longer than ~800 residues may fail or have reduced quality
• Single-chain only: both ESMFold and standard AlphaFold predict monomers; complex prediction requires AlphaFold-Multimer (not available via these tools)
• Disordered regions: pLDDT < 50 indicates intrinsically disordered regions (IDRs) — do not interpret these as structured
• No dynamics: predicted structures are static; do not represent conformational flexibility or allosteric changes
• Novel folds: ESMFold may struggle with proteins having no homologs in training data
• AlphaFold DB coverage: some recently characterized proteins may not yet be in the AlphaFold database