Xenobiotic acyltransferase (XAT): The XAT class of hexapeptide acyltransferases is composed of a large number of microbial enzymes that catalyze the CoA-dependent acetylation of a variety of hydroxyl-bearing acceptors such as chloramphenicol and streptogramin, among others. Members of this class of enzymes include Enterococcus faecium streptogramin A acetyltransferase and Pseudomonas aeruginosa chloramphenicol acetyltransferase. They contain repeated copies of a six-residue hexapeptide repeat sequence motif (X-[STAV]-X-[LIV]-[GAED]-X) and adopt a left-handed parallel beta helix (LbH) structure. The active enzyme is a trimer with CoA and substrate binding sites at the interface of two separate LbH subunits. XATs are implicated in inactivating xenobiotics leading to xenobiotic resistance in patients.
Comment:Active streptogramin acetyltransferase is homotrimeric, with active sites located at the interface between two LbH subunits. The trimer structure contains three active sites and each subunit contributes to two active sites via residues located on two surfaces.
Structure:1KHR_A; Enterococcus faecium streptogramin acetyltransferase Vat(D) binds CoA and substrate Virginiamycin; defined at 3.5A contacts. Shown are two active sites within the trimer. - View structure with Cn3D