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Protein Structure Visualization Expert Agent

Since v0.2 - Protein structure analysis with PyMOL visualization and BioPython integration

Agent Name: protein_structure_visualization_expert_agent Display Name: Protein Structure Visualization Expert Factory Function: lobster.agents.protein_structure_visualization_expert.protein_structure_visualization_expert

Overview

The Protein Structure Visualization Expert is a specialized agent for fetching, visualizing, and analyzing 3D protein structures from the RCSB Protein Data Bank (PDB). It integrates PyMOL (open-source) for high-quality molecular visualizations and BioPython for structural analysis, enabling seamless linking between protein structures and omics datasets.

Version Note: This agent requires Lobster v0.2+ and is fully supported in both local and cloud modes (with limited interactive visualization in cloud).

Key Features

  • PDB Structure Fetching: Download protein structures by PDB ID with comprehensive metadata
  • PyMOL Integration: Generate professional 3D visualizations with customizable styles and colors
  • Structural Analysis: Calculate RMSD, secondary structure, geometry, and residue contacts
  • Omics Integration: Link protein structures to gene expression and proteomics data
  • Structure Comparison: Compare multiple protein structures and calculate structural similarity
  • Provenance Tracking: Full W3C-PROV compliant logging with Intermediate Representation (IR)

Architecture

Services (Stateless, 3-Tuple Pattern)

1. ProteinStructureFetchService

Location: lobster/tools/protein_structure_fetch_service.py

Handles fetching protein structures from RCSB PDB with caching and metadata extraction.

Methods:

  • fetch_structure(pdb_id, format='cif', cache_dir, extract_metadata) → Tuple[Dict, Dict, AnalysisStep]
  • link_structures_to_genes(adata, gene_column, organism, max_structures_per_gene) → Tuple[AnnData, Dict, AnalysisStep]

Features:

  • PDB ID format validation (4-character alphanumeric)
  • Automatic caching to avoid redundant downloads
  • BioPython-based structure parsing
  • Metadata extraction (resolution, organism, experiment method)
  • Gene-to-structure mapping via PDB search API

2. PyMOLVisualizationService

Location: lobster/tools/pymol_visualization_service.py

Creates high-quality 3D visualizations using PyMOL (open-source).

Methods:

  • visualize_structure(structure_file, mode, style, color_by, output_image, width, height, execute_commands) → Tuple[Dict, Dict, AnalysisStep]
  • check_pymol_installation() → Dict[str, Any]

Features:

  • Multiple representation styles: cartoon, surface, sticks, spheres, ribbon, lines
  • Multiple coloring schemes: chain, secondary_structure, bfactor, element
  • Interactive and batch modes (GUI or headless image generation)
  • PyMOL command script generation (.pml files)
  • Automatic PyMOL installation detection
  • Graceful fallback when PyMOL is not installed
  • High-resolution image export (customizable dimensions)
  • Non-blocking GUI launch for interactive exploration

3. StructureAnalysisService

Location: lobster/tools/structure_analysis_service.py

Performs structural analysis using BioPython.

Methods:

  • analyze_structure(structure_file, analysis_type, chain_id) → Tuple[Dict, Dict, AnalysisStep]
  • calculate_rmsd(structure_file1, structure_file2, chain_id1, chain_id2, align) → Tuple[Dict, Dict, AnalysisStep]

Features:

  • Secondary structure analysis (DSSP integration with fallback)
  • Geometric properties (center of mass, radius of gyration)
  • Residue contact analysis (spatial proximity)
  • RMSD calculation with optional superposition alignment
  • BioPython Superimposer for structural alignment

Agent Tools

1. fetch_protein_structure

Purpose: Download protein structure from RCSB PDB

Parameters:

  • pdb_id (str, required): PDB identifier (e.g., '1AKE', '4HHB')
  • format (str, default='cif'): File format ('pdb' or 'cif')

Returns: Summary with metadata, file paths, and structural properties

Example:

fetch_protein_structure("1AKE")
fetch_protein_structure("4HHB", format="pdb")

Output Includes:

  • PDB ID, title, organism
  • Experiment method and resolution
  • Number of chains, residues, atoms
  • File path and size
  • Publication DOI and citation

2. link_to_expression_data

Purpose: Link gene expression data to protein structures

Parameters:

  • modality_name (str, required): Name of modality with gene/protein data
  • gene_column (str, default='gene_symbol'): Column in adata.var with gene symbols
  • organism (str, default='Homo sapiens'): Source organism for structure search
  • max_structures_per_gene (int, default=5): Maximum structures per gene

Returns: Summary of structure links created

Example:

link_to_expression_data("rna_seq_normalized")
link_to_expression_data("proteomics_data", gene_column="protein_name", organism="Mus musculus")

Output Includes:

  • Genes searched and genes with structures found
  • Total structures found and average per gene
  • New modality name with structure links
  • Columns added: pdb_structures (comma-separated PDB IDs), has_structure (boolean)

3. visualize_with_pymol

Purpose: Create high-quality 3D visualization using PyMOL

Parameters:

  • pdb_id (str, required): PDB ID of structure (must be fetched first)
  • mode (str, default='interactive'): Execution mode
    • Options: 'interactive' (launch GUI for exploration), 'batch' (save PNG and exit)
  • style (str, default='cartoon'): Representation style
    • Options: 'cartoon', 'surface', 'sticks', 'spheres', 'ribbon', 'lines'
  • color_by (str, default='chain'): Coloring scheme
    • Options: 'chain', 'secondary_structure', 'bfactor', 'element'
  • width (int, default=1920): Image width in pixels
  • height (int, default=1080): Image height in pixels
  • execute (bool, default=True): Execute PyMOL commands if installed
  • highlight_residues (str, optional): Residues to highlight (e.g., "15,42,89" or "A:15-20,B:42")
  • highlight_color (str, default='red'): Color for highlighted residues
  • highlight_style (str, default='sticks'): Visualization style for highlights
  • highlight_groups (str, optional): Multiple highlight groups (format: "residues|color|style;...")

Returns: Visualization metadata with file paths and execution status

Examples:

# Basic visualization
visualize_with_pymol("1AKE")  # Interactive mode by default
visualize_with_pymol("4HHB", mode="batch", style="surface", color_by="bfactor")
visualize_with_pymol("1AKE", mode="interactive")  # Launch GUI for exploration

# Residue highlighting - Single group
visualize_with_pymol("1AKE", highlight_residues="15,42,89", highlight_color="red", highlight_style="sticks")

# Residue highlighting - Chain-specific
visualize_with_pymol("4HHB", highlight_residues="A:15-20,B:30-35", highlight_color="yellow")

# Residue highlighting - Multiple groups
visualize_with_pymol("1AKE", highlight_groups="15,42|red|sticks;100-120|blue|surface;200,215|green|spheres")

Output Includes:

  • Visualization settings (mode, style, color scheme, dimensions)
  • Command script path (.pml file)
  • Output image path (.png file)
  • Execution status and PyMOL installation info
  • Process ID (PID) for interactive mode

4. analyze_protein_structure

Purpose: Analyze protein structure properties

Parameters:

  • pdb_id (str, required): PDB ID of structure (must be fetched first)
  • analysis_type (str, default='secondary_structure'): Type of analysis
    • Options: 'secondary_structure', 'geometry', 'residue_contacts'
  • chain_id (str, optional): Specific chain to analyze (None for all chains)

Returns: Analysis results with structural properties

Example:

analyze_protein_structure("1AKE")
analyze_protein_structure("4HHB", analysis_type="geometry")
analyze_protein_structure("1AKE", analysis_type="residue_contacts", chain_id="A")

Analysis Types:

Secondary Structure

  • Helix, sheet, coil percentages
  • Per-residue secondary structure assignments
  • Requires DSSP binary (with fallback)

Geometry

  • Total atoms and chains
  • Center of mass
  • Radius of gyration
  • Per-chain geometric properties

Residue Contacts

  • Total residue-residue contacts (default cutoff: 8 Å)
  • Average contacts per residue
  • Contact distance matrix

5. compare_structures

Purpose: Compare two protein structures by RMSD

Parameters:

  • pdb_id1 (str, required): First PDB ID (must be fetched)
  • pdb_id2 (str, required): Second PDB ID (must be fetched)
  • align (bool, default=True): Align structures before RMSD calculation
  • chain_id1 (str, optional): Specific chain in first structure
  • chain_id2 (str, optional): Specific chain in second structure

Returns: RMSD and structural comparison results

Example:

compare_structures("1AKE", "4AKE")
compare_structures("1AKE", "4AKE", align=False)
compare_structures("4HHB", "2HHB", chain_id1="A", chain_id2="A")

RMSD Interpretation:

  • < 1.0 Å: Nearly identical structures
  • 1-2 Å: Very similar (close homologs, small conformational changes)
  • 2-3 Å: Similar (homologs, moderate conformational changes)
  • 3-5 Å: Moderately similar (distant homologs, domain movements)
  • > 5 Å: Different structures (large conformational changes)

Workflows

Basic Workflow: Fetch and Visualize

1. User: "Visualize protein structure 1AKE"
2. Supervisor → Protein Structure Visualization Expert
3. Agent: fetch_protein_structure("1AKE")
4. Agent: visualize_with_pymol("1AKE", mode="interactive", style="cartoon")
5. Agent → Supervisor: Results with visualization paths
6. Supervisor → User: Visualization complete

Advanced Workflow: Link Structures to Expression Data

1. User: "Link structures to my RNA-seq data"
2. Supervisor → Protein Structure Visualization Expert
3. Agent: link_to_expression_data("rna_seq_normalized", organism="Homo sapiens")
4. Agent creates new modality with structure mappings
5. Agent → Supervisor: Linking results (e.g., "50 genes linked to 75 structures")
6. Supervisor → User: Structure links created

Comparative Workflow: RMSD Analysis

1. User: "Compare structures 1AKE and 4AKE"
2. Supervisor → Protein Structure Visualization Expert
3. Agent: fetch_protein_structure("1AKE")
4. Agent: fetch_protein_structure("4AKE")
5. Agent: compare_structures("1AKE", "4AKE", align=True)
6. Agent → Supervisor: RMSD results (e.g., "RMSD = 1.2 Å, very similar")
7. Supervisor → User: Comparison complete

PyMOL Installation

Why PyMOL?

PyMOL is a professional open-source molecular visualization tool that provides:

  • High-quality molecular graphics
  • Publication-ready images
  • Comprehensive visualization commands
  • Python API for automation
  • Interactive GUI mode for real-time exploration
  • Active open-source community

Automated Installation (Recommended)

Docker Container (Cloud Deployments)

PyMOL is pre-installed in the Lobster Docker image. No action required.

Verify installation:

docker run -it omicsos/lobster:latest pymol -c -Q

Local Development (macOS/Linux)

Install PyMOL via Makefile target:

# Install PyMOL automatically
make install-pymol

This command will:

  • Detect your operating system (macOS or Linux)
  • Install PyMOL via the appropriate package manager
  • Verify the installation

What it does:

  • macOS: Uses Homebrew with brewsci/bio tap
  • Linux: Uses apt-get (Ubuntu/Debian) or dnf (Fedora/RHEL)
  • Homebrew on Linux: Fallback if native package manager unavailable

Requirements:

  • macOS: Homebrew must be installed
  • Linux: sudo access for package installation

Installation output:

$ make install-pymol
🔬 Installing PyMOL for protein structure visualization...
🍎 macOS detected - Installing via Homebrew...
📦 Installing PyMOL...
✅ PyMOL installed successfully!

🎉 PyMOL installation complete!
💡 Test with: pymol -c -Q

Manual Installation (Fallback)

If automated installation is not available or fails, you can install PyMOL manually.

macOS

# Install via Homebrew (recommended)
brew install brewsci/bio/pymol

# Or download from official website
# https://pymol.org/

# After installation, PyMOL is automatically added to PATH

Linux

# Ubuntu/Debian
sudo apt-get update
sudo apt-get install pymol

# Or via Homebrew on Linux
brew install brewsci/bio/pymol

# Arch Linux
sudo pacman -S pymol

# Fedora/CentOS/RHEL
sudo dnf install pymol

Windows

1. Download installer from https://pymol.org/
2. Run installer and follow instructions
3. PyMOL executable will be added to Start Menu
4. Optionally add to PATH via System Environment Variables

Manual Execution Without Installation

Even without PyMOL installed, the agent generates .pml command scripts that can be:

  • Executed manually when PyMOL is installed
  • Modified for custom visualizations
  • Used as templates for batch processing

Examples:

# Interactive mode (with GUI)
pymol 1AKE_cartoon_chain_commands.pml

# Batch mode (headless, save image and exit)
pymol -c 1AKE_cartoon_chain_commands.pml

Integration with Omics Workflows

Single-Cell RNA-seq Integration

Link protein structures to highly expressed genes:

1. Run single-cell analysis (clustering, DE analysis)
2. Identify top expressed genes
3. Use link_to_expression_data() to find structures
4. Visualize structures for key marker genes

Proteomics Integration

Link structures to identified proteins:

1. Run proteomics analysis (quantification, DE)
2. Identify significantly changing proteins
3. Use link_to_expression_data() with protein_name column
4. Compare structures of protein variants

Multi-Omics Integration

Cross-reference structures across modalities:

1. Link structures to both RNA-seq and proteomics
2. Identify genes/proteins with structures in both datasets
3. Visualize structures colored by expression levels
4. Compare structural features with functional changes

Performance and Caching

Structure Caching

  • First fetch: Downloads from PDB, stores in protein_structures/ directory
  • Subsequent fetches: Uses cached file (instant)
  • Cache location: Workspace directory or current directory
  • Cache benefits: Avoids redundant downloads, faster workflow iterations

PDB Provider Rate Limits

  • Rate limit: 5 requests/second (RCSB PDB API limit)
  • No authentication: Public PDB API requires no API key
  • Batch operations: Use link_to_expression_data() for efficient batch queries

PyMOL Performance

  • Command scripts: Generated instantly (no execution delay)
  • Interactive mode: GUI launches in 2-5 seconds (non-blocking)
  • Batch mode (image generation): 5-30 seconds per structure (if PyMOL is installed)
  • Headless mode: PyMOL runs without GUI for automation (use pymol -c)
  • Parallel execution: Multiple structures can be visualized in parallel

Error Handling

Common Errors and Solutions

1. Invalid PDB ID

Error: Invalid PDB ID format: XYZ. Must be 4 alphanumeric characters.

Solution: Ensure PDB ID is exactly 4 characters (e.g., '1AKE', not '1AK' or '1AKEE')

2. Structure Not Found

Error: Failed to download structure 1XYZ from PDB

Solution: Verify PDB ID exists at https://www.rcsb.org/structure/1XYZ

3. PyMOL Not Installed

Error: PyMOL not found. Install with: brew install brewsci/bio/pymol

Solution: Install PyMOL or use generated command scripts manually

4. Gene Column Not Found

Error: Gene column 'gene_symbol' not found in adata.var

Solution: Check available columns with adata.var.columns and specify correct column name

5. DSSP Not Available

Warning: DSSP not available. Using simplified analysis.

Solution: Install DSSP for secondary structure analysis:

conda install -c salilab dssp

API Reference

ProteinStructureFetchService

from lobster.tools.protein_structure_fetch_service import ProteinStructureFetchService

service = ProteinStructureFetchService()

# Fetch structure
structure_data, stats, ir = service.fetch_structure(
    pdb_id="1AKE",
    format="cif",
    cache_dir=Path("protein_structures"),
    extract_metadata=True,
    data_manager=data_manager
)

# Link structures to genes
adata_linked, stats, ir = service.link_structures_to_genes(
    adata=adata,
    gene_column="gene_symbol",
    organism="Homo sapiens",
    max_structures_per_gene=5,
    data_manager=data_manager
)

PyMOLVisualizationService

from lobster.tools.pymol_visualization_service import PyMOLVisualizationService

service = PyMOLVisualizationService()

# Check installation
install_status = service.check_pymol_installation()

# Create visualization (batch mode - save PNG)
viz_data, stats, ir = service.visualize_structure(
    structure_file=Path("1AKE.cif"),
    mode="batch",
    style="cartoon",
    color_by="chain",
    output_image=Path("output.png"),
    width=1920,
    height=1080,
    execute_commands=True
)

# Or interactive mode (launch GUI)
viz_data, stats, ir = service.visualize_structure(
    structure_file=Path("1AKE.cif"),
    mode="interactive",
    style="cartoon",
    color_by="chain",
    execute_commands=True
)

StructureAnalysisService

from lobster.tools.structure_analysis_service import StructureAnalysisService

service = StructureAnalysisService()

# Analyze structure
analysis_results, stats, ir = service.analyze_structure(
    structure_file=Path("1AKE.cif"),
    analysis_type="secondary_structure",
    chain_id="A"
)

# Calculate RMSD
rmsd_results, stats, ir = service.calculate_rmsd(
    structure_file1=Path("1AKE.cif"),
    structure_file2=Path("4AKE.cif"),
    align=True
)

Best Practices

1. PDB ID Validation

Always use uppercase 4-character PDB IDs:

# Good
fetch_protein_structure("1AKE")

# Bad
fetch_protein_structure("1ake")  # Works but not consistent
fetch_protein_structure("1AK")   # Error: too short

2. Structure Caching

Leverage caching for iterative workflows:

# First run: downloads structure
fetch_protein_structure("1AKE")

# Subsequent runs: uses cache (instant)
visualize_with_pymol("1AKE", mode="interactive", style="cartoon")
visualize_with_pymol("1AKE", mode="batch", style="surface")  # No re-download

3. PyMOL Fallback

Generate scripts even without PyMOL:

# Script generation always works
visualize_with_pymol("1AKE", execute=False)

# Execute manually later when PyMOL is installed
# Interactive mode: pymol 1AKE_commands.pml
# Batch mode: pymol -c 1AKE_commands.pml

4. Gene-Structure Linking

Search by organism for better results:

# Specific organism
link_to_expression_data("adata", organism="Homo sapiens")

# Mouse data
link_to_expression_data("adata", organism="Mus musculus")

5. RMSD Interpretation

Use alignment for meaningful comparisons:

# With alignment (recommended)
compare_structures("1AKE", "4AKE", align=True)

# Without alignment (only for pre-aligned structures)
compare_structures("1AKE", "4AKE", align=False)

Provenance and Reproducibility

All structure operations generate Intermediate Representation (IR) with:

  • Operation: Specific operation performed (e.g., 'pdb.fetch_structure')
  • Parameters: All parameters used (pdb_id, format, style, etc.)
  • Code Template: Jinja2 template for notebook export
  • Imports: Required Python imports
  • Parameter Schema: Papermill-injectable parameters with validation

Notebook Export:

# Export pipeline to Jupyter notebook
data_manager.export_notebook("protein_structure_pipeline.ipynb")

# Execute notebook with different PDB ID
papermill protein_structure_pipeline.ipynb output.ipynb -p pdb_id "4HHB"

Troubleshooting

Issue: "Structure file not found"

  • Ensure structure was fetched first with fetch_protein_structure()
  • Check cache directory permissions
  • Verify file path in structure_data dictionary

Issue: "PyMOL execution timed out"

  • Large structures may take longer to render (batch mode)
  • Increase timeout in service configuration
  • Use execute=False to generate script without execution
  • For interactive mode, the GUI may take 2-5 seconds to launch

Issue: "No structures found for genes"

  • Check organism name (use Latin names: "Homo sapiens", "Mus musculus")
  • Verify gene symbols are standard (HGNC for human, MGI for mouse)
  • Try reducing max_structures_per_gene for faster queries

Issue: "RMSD calculation failed"

  • Ensure both structures have been fetched
  • Check chain IDs exist in structures
  • Verify structures have matching residues (homologs, not random proteins)

Examples

Example 1: Basic Structure Visualization

# Fetch and visualize adenylate kinase
fetch_protein_structure("1AKE")
visualize_with_pymol("1AKE", mode="interactive", style="cartoon", color_by="secondary_structure")

Example 2: Comparative Analysis

# Compare open and closed conformations of adenylate kinase
fetch_protein_structure("1AKE")  # Open form
fetch_protein_structure("4AKE")  # Closed form
compare_structures("1AKE", "4AKE", align=True)
# Output: RMSD = 1.2 Å (moderate conformational change)

Example 3: RNA-seq Integration

# After RNA-seq analysis
link_to_expression_data("rna_seq_normalized", organism="Homo sapiens")

# Visualize top expressed genes with structures
# Filter: adata[adata.var['has_structure']]

Example 4: Protein Family Analysis

# Fetch multiple family members
fetch_protein_structure("1AKE")
fetch_protein_structure("2AKE")
fetch_protein_structure("3AKE")

# Pairwise RMSD comparisons
compare_structures("1AKE", "2AKE")
compare_structures("1AKE", "3AKE")
compare_structures("2AKE", "3AKE")

Example 5: Residue Highlighting for Disease Mutations and Functional Sites

# Fetch structure
fetch_protein_structure("1AKE")

# Example 1: Highlight disease mutation sites in red
# Single residue group - useful for showing known pathogenic variants
visualize_with_pymol(
    "1AKE",
    mode="batch",
    style="cartoon",
    color_by="chain",
    highlight_residues="15,42,89",
    highlight_color="red",
    highlight_style="sticks"
)

# Example 2: Chain-specific highlighting for protein-protein interfaces
# Highlight interface residues in hemoglobin subunits
fetch_protein_structure("4HHB")
visualize_with_pymol(
    "4HHB",
    highlight_residues="A:15-20,A:42,B:30-35,B:50",
    highlight_color="yellow",
    highlight_style="sticks"
)

# Example 3: Multiple highlight groups for complex functional annotation
# Show binding site (red), catalytic residues (blue), and allosteric site (green)
visualize_with_pymol(
    "1AKE",
    mode="interactive",  # Launch GUI for interactive exploration
    highlight_groups="15,42,89|red|sticks;100-120|blue|surface;200,215,230|green|spheres"
)

# Example 4: Combining with different color schemes
# Highlight active site residues while showing B-factors for the rest
visualize_with_pymol(
    "1AKE",
    style="cartoon",
    color_by="bfactor",  # Color by temperature factors
    highlight_residues="100-120",  # Active site region
    highlight_color="red",
    highlight_style="sticks"
)

Use Cases for Residue Highlighting:

  • Disease Mutations: Highlight known pathogenic variants from ClinVar or GWAS studies
  • Binding Sites: Show ligand or substrate binding pockets
  • Active Sites: Emphasize catalytic residues (e.g., catalytic triad in proteases)
  • Post-Translational Modifications: Highlight phosphorylation, methylation, or acetylation sites
  • Protein-Protein Interfaces: Show interaction residues in multi-chain complexes
  • Conservation Analysis: Highlight evolutionarily conserved residues

Related Documentation

References

Last Updated: 2025-01-15 Version: 1.0.0 Maintainer: Lobster Development Team

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