protein Collagen collagen *C(N)C(=O)N[C@H](*)C(=O)N1CCC[C@H]1C(=O)NC(*)C(=O)O CHEBI:3815 Collagen chebi_ontology cas:9064-67-9 kegg.compound:C00211 C4H6N2O3R2(C7H9N2O2R)n Further classification will be integrated for this class