PDB Database

Overview

RCSB PDB is the worldwide repository for 3D structural data of biological macromolecules. Search for structures, retrieve coordinates and metadata, perform sequence and structure similarity searches across 200,000+ experimentally determined structures and computed models.

Scripts

scripts/query_pdb.py — RCSB Search + Data + file APIs (stdlib only, JSON to stdout):

python scripts/query_pdb.py search hemoglobin --rows 25     # full-text search (entry IDs)
python scripts/query_pdb.py entry 4HHB                      # entry metadata
python scripts/query_pdb.py download 4HHB --format cif      # download coordinates

When to Use This Skill

This skill should be used when:

• Searching for protein or nucleic acid 3D structures by text, sequence, or structural similarity
• Downloading coordinate files in PDB, mmCIF, or BinaryCIF formats
• Retrieving structural metadata, experimental methods, or quality metrics
• Performing batch operations across multiple structures
• Integrating PDB data into computational workflows for drug discovery, protein engineering, or structural biology research

Core Capabilities

1. Searching for Structures

Find PDB entries using various search criteria:

Text Search: Search by protein name, keywords, or descriptions

from rcsbapi.search import TextQuery
query = TextQuery("hemoglobin")
results = list(query())
print(f"Found {len(results)} structures")

Attribute Search: Query specific properties (organism, resolution, method, etc.)

from rcsbapi.search import AttributeQuery
from rcsbapi.search import search_attributes as attrs

# Find human protein structures (idiomatic form — recommended)
query = attrs.rcsb_entity_source_organism.scientific_name == "Homo sapiens"
results = list(query())

# OR explicit AttributeQuery with a dotted-path STRING (not the Attr object):
query = AttributeQuery(
    attribute="rcsb_entity_source_organism.scientific_name",
    operator="exact_match",
    value="Homo sapiens",
)
results = list(query())

Sequence Similarity: Find structures similar to a given sequence

from rcsbapi.search import SeqSimilarityQuery

query = SeqSimilarityQuery(
    value="MTEYKLVVVGAGGVGKSALTIQLIQNHFVDEYDPTIEDSYRKQVVIDGETCLLDILDTAGQEEYSAMRDQYMRTGEGFLCVFAINNTKSFEDIHHYREQIKRVKDSEDVPMVLVGNKCDLPSRTVDTKQAQDLARSYGIPFIETSAKTRQGVDDAFYTLVREIRKHKEKMSKDGKKKKKKSKTKCVIM",
    evalue_cutoff=0.1,
    identity_cutoff=0.9,
    sequence_type="protein"
)
results = list(query())

Structure Similarity: Find structures with similar 3D geometry

from rcsbapi.search import StructSimilarityQuery

query = StructSimilarityQuery(
    structure_search_type="entry",
    entry_id="4HHB"  # Hemoglobin
)
results = list(query())

Combining Queries: Use logical operators to build complex searches

from rcsbapi.search import search_attributes as attrs

# High-resolution human proteins
query1 = attrs.rcsb_entity_source_organism.scientific_name == "Homo sapiens"
query2 = attrs.rcsb_entry_info.resolution_combined < 2.0
combined_query = query1 & query2  # AND operation
results = list(combined_query())

2. Retrieving Structure Data

Access detailed information about specific PDB entries:

Basic Entry Information:

from rcsbapi.data import DataQuery

# Get entry-level data
query = DataQuery(
    input_type="entries",
    input_ids=["4HHB"],
    return_data_list=["struct.title", "exptl.method"],
)
data = query.exec()  # synchronous; returns a dict
entry = data["data"]["entries"][0]
print(entry["struct"]["title"])
print(entry["exptl"][0]["method"])

Polymer Entity Information:

from rcsbapi.data import DataQuery

# Get protein/nucleic acid information
query = DataQuery(
    input_type="polymer_entities",
    input_ids=["4HHB_1"],
    return_data_list=["entity_poly.pdbx_seq_one_letter_code"],
)
data = query.exec()
entity = data["data"]["polymer_entities"][0]
print(entity["entity_poly"]["pdbx_seq_one_letter_code"])

Building Queries (GraphQL under the hood):

from rcsbapi.data import DataQuery

# DataQuery builds the GraphQL query for you from input_type/input_ids/return_data_list;
# there is no separate fetch(query_type="graphql", ...) entry point.
query = DataQuery(
    input_type="entries",
    input_ids=["4HHB"],
    return_data_list=[
        "struct.title",
        "exptl.method",
        "rcsb_entry_info.resolution_combined",
        "rcsb_entry_info.deposited_atom_count",
    ],
)
# Inspect the auto-generated GraphQL / open it in the editor:
print(query.get_editor_link())
data = query.exec()

3. Downloading Structure Files

Retrieve coordinate files in various formats:

Download Methods:

• PDB format (legacy text format): https://files.rcsb.org/download/{PDB_ID}.pdb
• mmCIF format (modern standard): https://files.rcsb.org/download/{PDB_ID}.cif
• BinaryCIF (compressed binary): Use ModelServer API for efficient access
• Biological assembly: https://files.rcsb.org/download/{PDB_ID}.pdb1 (for assembly 1)

Example Download:

import requests

pdb_id = "4HHB"

# Download PDB format
pdb_url = f"https://files.rcsb.org/download/{pdb_id}.pdb"
response = requests.get(pdb_url)
with open(f"{pdb_id}.pdb", "w") as f:
    f.write(response.text)

# Download mmCIF format
cif_url = f"https://files.rcsb.org/download/{pdb_id}.cif"
response = requests.get(cif_url)
with open(f"{pdb_id}.cif", "w") as f:
    f.write(response.text)

4. Working with Structure Data

Common operations with retrieved structures:

Parse and Analyze Coordinates: Use BioPython or other structural biology libraries to work with downloaded files:

from Bio.PDB import PDBParser

parser = PDBParser()
structure = parser.get_structure("protein", "4HHB.pdb")

# Iterate through atoms
for model in structure:
    for chain in model:
        for residue in chain:
            for atom in residue:
                print(atom.get_coord())

Extract Metadata:

from rcsbapi.data import DataQuery

# Get experimental details
query = DataQuery(
    input_type="entries",
    input_ids=["4HHB"],
    return_data_list=[
        "rcsb_entry_info.resolution_combined",
        "exptl.method",
        "rcsb_accession_info.deposit_date",
    ],
)
data = query.exec()["data"]["entries"][0]

resolution = data.get("rcsb_entry_info", {}).get("resolution_combined")
method = data.get("exptl", [{}])[0].get("method")
deposition_date = data.get("rcsb_accession_info", {}).get("deposit_date")

print(f"Resolution: {resolution} Å")
print(f"Method: {method}")
print(f"Deposited: {deposition_date}")

5. Batch Operations

Process multiple structures efficiently:

from rcsbapi.data import DataQuery

pdb_ids = ["4HHB", "1MBN", "1GZX"]  # Hemoglobin, myoglobin, etc.

# A single DataQuery can fetch all entries at once
query = DataQuery(
    input_type="entries",
    input_ids=pdb_ids,
    return_data_list=[
        "rcsb_id",
        "struct.title",
        "rcsb_entry_info.resolution_combined",
        "rcsb_entity_source_organism.scientific_name",
    ],
)

results = {}
for data in query.exec()["data"]["entries"]:
    pdb_id = data["rcsb_id"]
    results[pdb_id] = {
        "title": data["struct"]["title"],
        "resolution": data.get("rcsb_entry_info", {}).get("resolution_combined"),
        "organism": data.get("rcsb_entity_source_organism", [{}])[0].get("scientific_name")
    }

# Display results
for pdb_id, info in results.items():
    print(f"\n{pdb_id}: {info['title']}")
    print(f"  Resolution: {info['resolution']} Å")
    print(f"  Organism: {info['organism']}")

Python Package Installation

Install the official RCSB PDB Python API client (rcsb-api, current major version 1.x; examples here target >=1.7):

uv pip install "rcsb-api>=1.7"

The rcsb-api package provides unified access to both Search and Data APIs through the rcsbapi.search and rcsbapi.data modules. (The older rcsbsearchapi package is superseded by rcsb-api and its import rcsbsearchapi path is gone — prefer rcsb-api for new code.)

The scripts/query_pdb.py helper needs none of this — it hits the public REST APIs with only the Python standard library.

Common Use Cases

Drug Discovery

• Search for structures of drug targets
• Analyze ligand binding sites
• Compare protein-ligand complexes
• Identify similar binding pockets

Protein Engineering

• Find homologous structures for modeling
• Analyze sequence-structure relationships
• Compare mutant structures
• Study protein stability and dynamics

Structural Biology Research

• Download structures for computational analysis
• Build structure-based alignments
• Analyze structural features (secondary structure, domains)
• Compare experimental methods and quality metrics

Education and Visualization

• Retrieve structures for teaching
• Generate molecular visualizations
• Explore structure-function relationships
• Study evolutionary conservation

Key Concepts

PDB ID: Unique 4-character identifier (e.g., "4HHB") for each structure entry. AlphaFold and ModelArchive entries start with "AF_" or "MA_" prefixes.

mmCIF/PDBx: Modern file format that uses key-value structure, replacing legacy PDB format for large structures.

Biological Assembly: The functional form of a macromolecule, which may contain multiple copies of chains from the asymmetric unit.

Resolution: Measure of detail in crystallographic structures (lower values = higher detail). Typical range: 1.5-3.5 Å for high-quality structures.

Entity: A unique molecular component in a structure (protein chain, DNA, ligand, etc.).

Resources

This skill includes reference documentation in the references/ directory:

references/api_reference.md

Comprehensive API documentation covering:

• Detailed API endpoint specifications
• Advanced query patterns and examples
• Data schema reference
• Rate limiting and best practices
• Troubleshooting common issues

Use this reference when you need in-depth information about API capabilities, complex query construction, or detailed data schema information.

Additional Resources

• RCSB PDB Website: https://www.rcsb.org
• PDB-101 Educational Portal: https://pdb101.rcsb.org
• API Documentation: https://www.rcsb.org/docs/programmatic-access/web-apis-overview
• Python Package Docs: https://rcsbapi.readthedocs.io/
• Data API Documentation: https://data.rcsb.org/
• GitHub Repository: https://github.com/rcsb/py-rcsb-api