The CDD is a resource for the annotation of functional units in proteins. Its collection of domain models includes a set curated by NCBI, which utilizes 3D structure to provide insights into sequence/structure/function relationships.
Learn more about Conserved Domains and Protein Classification.
HomoloGene is a system for automated detection of homologs among the annotated genes of several completely sequenced eukaryotic genomes.
The Protein Clusters database is a collection of protein sequences, consisting of Reference Sequence proteins encoded by complete prokaryotic and organelle plasmids and genomes. The database provides easy access to annotated information, publication, domains, structures, external links, and analysis tools including multiple alignments, phylogenetic trees, and genomic neighborhoods (ProtMap).