CATH-Gene3D is a protein structure classification and bioinformatics resource associated with UCL. It organizes protein domains from the Protein Data Bank into a hierarchy, grouping domains into superfamilies when evidence indicates they share a common evolutionary ancestor. The resource combines structural classifications with sequence and functional annotations to help researchers investigate protein structure, evolution, function, and conserved sites.

Users can search by protein sequence, text, identifier, keyword, or PDB structure, and browse the CATH hierarchy. Sequence searches identify matching domain structures and superfamilies, while CATH-Gene3D FunFams group domains likely to share functions and support predictions with Enzyme Commission and Gene Ontology annotations. The site also offers tools and information for exploring sequence and structural diversity, conserved residues, and protein family relationships. Data downloads, web services, tutorials, release statistics, and documentation support further research and analysis. CATH provides core classification files alongside daily updates and limited annotations for newer structures through CATH-B. Its classifications and domain predictions cover experimental and predicted structural data, including annotations associated with AlphaFold resources.