RCSB Protein Data Bank API Guide

Overview

The RCSB Protein Data Bank (PDB) is the single global archive for experimentally determined 3D structures of biological macromolecules. It hosts over 200,000 structures resolved by X-ray crystallography, cryo-EM, NMR spectroscopy, and other methods. Each entry includes atomic coordinates, experimental metadata, polymer sequences, bound ligands, and literature references.

Two complementary APIs are available. The Data API (data.rcsb.org) serves structured entry metadata, polymer entities, and chemical components via RESTful GET endpoints. The Search API (search.rcsb.org) supports full-text, attribute-based, sequence similarity, and structure similarity searches.

Authentication

No authentication required. Both APIs are freely accessible without API keys, tokens, or registration.

Core Endpoints

Data API: Get Entry by PDB ID

Retrieve metadata for a structure including experimental method, resolution, citations, and bound components.

• URL: GET https://data.rcsb.org/rest/v1/core/entry/{pdb_id}

bash
curl "https://data.rcsb.org/rest/v1/core/entry/4HHB"

• Response (key fields):

json
{
  "rcsb_id": "4HHB",
  "struct": {
    "title": "THE CRYSTAL STRUCTURE OF HUMAN DEOXYHAEMOGLOBIN AT 1.74 ANGSTROMS RESOLUTION"
  },
  "exptl": [{"method": "X-RAY DIFFRACTION"}],
  "rcsb_entry_info": {
    "deposited_atom_count": 4779,
    "molecular_weight": 64.74,
    "polymer_composition": "heteromeric protein",
    "polymer_entity_count_protein": 2,
    "resolution_combined": [1.74],
    "nonpolymer_bound_components": ["HEM"]
  }
}

Data API: Get Polymer Entity

Retrieve protein/nucleic acid entity details including sequence, organism, and gene info.

• URL: GET https://data.rcsb.org/rest/v1/core/polymer_entity/{pdb_id}/{entity_id}

bash
curl "https://data.rcsb.org/rest/v1/core/polymer_entity/4HHB/1"

• Response (key fields):

json
{
  "entity_poly": {
    "pdbx_seq_one_letter_code_can": "VLSPADKTNVKAAWGKVGAHAGEYGAEALERMFLSFPTTKTYFPHFDLSH...",
    "rcsb_entity_polymer_type": "Protein",
    "rcsb_sample_sequence_length": 141,
    "type": "polypeptide(L)"
  },
  "entity_src_gen": [{
    "gene_src_common_name": "Human",
    "pdbx_gene_src_scientific_name": "Homo sapiens",
    "pdbx_gene_src_ncbi_taxonomy_id": "9606"
  }]
}

Data API: Get Chemical Component

Retrieve ligand or small molecule metadata by component ID.

• URL: GET https://data.rcsb.org/rest/v1/core/chemcomp/{comp_id}

bash
curl "https://data.rcsb.org/rest/v1/core/chemcomp/HEM"

• Response (key fields):

json
{
  "rcsb_id": "HEM",
  "chem_comp": {
    "formula": "C34 H32 Fe N4 O4",
    "formula_weight": 616.487,
    "name": "PROTOPORPHYRIN IX CONTAINING FE",
    "type": "non-polymer"
  }
}

Search API: Full-Text Search

Search across all PDB entries with free-text queries. Returns ranked results by relevance.

• URL: POST https://search.rcsb.org/rcsbsearch/v2/query
• Headers: Content-Type: application/json
• Key body fields: query.type ("terminal"), query.service ("full_text", "text", "sequence", "structure"), query.parameters.value, return_type ("entry", "polymer_entity", "assembly"), request_options.paginate.start/rows

bash
curl -X POST "https://search.rcsb.org/rcsbsearch/v2/query" \
  -H "Content-Type: application/json" \
  -d '{
    "query": {
      "type": "terminal",
      "service": "full_text",
      "parameters": {"value": "hemoglobin"}
    },
    "return_type": "entry",
    "request_options": {
      "results_content_type": ["experimental"],
      "paginate": {"start": 0, "rows": 3}
    }
  }'

• Response:

json
{
  "query_id": "6f7192a6-d65b-4ff1-9d94-37b9600a8864",
  "result_type": "entry",
  "total_count": 8960,
  "result_set": [
    {"identifier": "3GOU", "score": 1.0},
    {"identifier": "6IHX", "score": 0.9995},
    {"identifier": "2PGH", "score": 0.9985}
  ]
}

For attribute-based searches, use "service": "text" with "attribute" and "operator" fields. Combine multiple criteria with "type": "group" and "logical_operator": "and".

Rate Limits

No formal rate limits or rate-limit headers are published. RCSB recommends reasonable request rates. For bulk data, use FTP downloads at https://files.rcsb.org/pub/pdb/ or ftp://ftp.wwpdb.org/pub/pdb/ instead of iterative API calls.

Academic Use Cases

• Structure-Based Drug Design: Retrieve target protein structures with bound ligands to analyze binding pockets, then search for similar structures to identify drug scaffolds.
• Comparative Structural Analysis: Search all structures of a protein family, compare resolution and methods, select the best template for homology modeling.
• Protein Engineering: Retrieve wild-type structures and cross-reference with mutant entries to analyze how mutations affect fold stability and ligand interactions.

Code Examples

Search and Retrieve Structures

python
import requests

# Search for kinase inhibitor structures
search_body = {
    "query": {"type": "terminal", "service": "full_text",
              "parameters": {"value": "tyrosine kinase inhibitor"}},
    "return_type": "entry",
    "request_options": {"results_content_type": ["experimental"],
                        "paginate": {"start": 0, "rows": 5}}
}
results = requests.post("https://search.rcsb.org/rcsbsearch/v2/query",
                        json=search_body).json()
print(f"Total hits: {results['total_count']}")

# Retrieve metadata for each hit
for hit in results["result_set"]:
    pdb_id = hit["identifier"]
    entry = requests.get(
        f"https://data.rcsb.org/rest/v1/core/entry/{pdb_id}").json()
    info = entry["rcsb_entry_info"]
    print(f"{pdb_id}: {entry['struct']['title'][:80]}")
    print(f"  Resolution: {info.get('resolution_combined', ['N/A'])[0]} A, "
          f"Method: {info['experimental_method']}")

Extract Polymer Sequences

python
import requests

pdb_id = "4HHB"
entry = requests.get(
    f"https://data.rcsb.org/rest/v1/core/entry/{pdb_id}").json()

for eid in range(1, entry["rcsb_entry_info"]["polymer_entity_count"] + 1):
    entity = requests.get(
        f"https://data.rcsb.org/rest/v1/core/polymer_entity/{pdb_id}/{eid}"
    ).json()
    poly = entity["entity_poly"]
    src = entity.get("rcsb_entity_source_organism", [{}])[0]
    print(f"Entity {eid}: {poly['rcsb_entity_polymer_type']} "
          f"({src.get('ncbi_scientific_name', 'N/A')})")
    print(f"  {poly['rcsb_sample_sequence_length']} residues: "
          f"{poly['pdbx_seq_one_letter_code_can'][:50]}...")

References

• Data API docs: https://data.rcsb.org/redoc/index.html
• Search API docs: https://search.rcsb.org/index.html
• RCSB PDB homepage: https://www.rcsb.org/
• Programmatic access guide: https://www.rcsb.org/docs/programmatic-access
• PDB file format: https://www.wwpdb.org/documentation/file-format
• Worldwide PDB: https://www.wwpdb.org/