Amidase_YiiX is a family of permuted papain-like amidases. It has amidase specificity for the amide bond between a lipid and an amino acid (or peptide). From the structure, a tetramer, each monomer is made up of a layered alpha-beta fold with a central, 6-stranded, antiparallel beta-sheet that is protected by helices on either side. The catalytic Cys154 in UniProtKB:Q74NK7, PDB:3kw0, is located on the N-terminus of helix alphaF. The two additional helices located above Cys154 contribute to the formation of the active site, where the lysine ligand is bound [1].

1: Structural analysis of papain-like NlpC/P60 superfamily enzymes with a circularly permuted topology reveals potential lipid binding sites. Xu Q, Rawlings ND, Chiu HJ, Jaroszewski L, Klock HE, Knuth MW, Miller MD, Elsliger MA, Deacon AM, Godzik A, Lesley SA, Wilson IA; PLoS One. 2011;6:e22013. PMID:21799766