RCSB PDB Data API
Provides structured access to the complete RCSB PDB holdings via REST and GraphQL interfaces. Given a known PDB identifier, callers can retrieve rich JSON metadata about entries, polymer entities, non-polymer entities (ligands), polymer entity instances (chains), assemblies, branched entities, and chemical components. The REST surface mirrors an OpenAPI/ReDoc contract while the GraphQL endpoint supports flexible field selection and nested queries.