title: Arylamine N-acetyltransferases in mycobacteria.
abstract: Polymorphic Human arylamine N-acetyltransferase (NAT2) inactivates the anti-tubercular drug isoniazid by acetyltransfer from acetylCoA. There are active NAT proteins encoded by homologous genes in mycobacteria including M. tuberculosis, M. bovis BCG, M. smegmatis and M. marinum. Crystallographic structures of NATs from M. smegmatis and M. marinum, as native enzymes and with isoniazid bound share a similar fold with the first NAT structure, Salmonella typhimurium NAT. There are three approximately equal domains and an active site essential catalytic triad of cysteine, histidine and aspartate in the first two domains. An acetyl group from acetylCoA is transferred to cysteine and then to the acetyl acceptor e.g. isoniazid. M. marinum NAT binds CoA in a more open mode compared with CoA binding to human NAT2. The structure of mycobacterial NAT may promote its role in synthesis of cell wall lipids, identified through gene deletion studies. NAT protein is essential for survival of M. bovis BCG in macrophage as are the proteins encoded by other genes in the same gene cluster (hsaA-D). HsaA-D degrade cholesterol, essential for mycobacterial survival inside macrophage. Nat expression remains to be fully understood but is co-ordinated with hsaA-D and other stress response genes in mycobacteria. Amide synthase genes in the streptomyces are also nat homologues. The amide synthases are predicted to catalyse intramolecular amide bond formation and creation of cyclic molecules, e.g. geldanamycin. Lack of conservation of the CoA binding cleft residues of M. marinum NAT suggests the amide synthase reaction mechanism does not involve a soluble CoA intermediate during amide formation and ring closure.
authors.affiliation: Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX13QT, UK. edith.sim@pharm.ox.ac.uk
authors.forename: Edith
authors.initials: E
authors.lastname: Sim
authors.forename: James
authors.initials: J
authors.lastname: Sandy
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Evangelopoulos
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Fullam
authors.forename: Sanjib
authors.initials: S
authors.lastname: Bhakta
authors.forename: Isaac
authors.initials: I
authors.lastname: Westwood
authors.forename: Anna
authors.initials: A
authors.lastname: Krylova
authors.forename: Nathan
authors.initials: N
authors.lastname: Lack
authors.forename: Martin
authors.initials: M
authors.lastname: Noble
mesh_terms: D000595:Amino Acid Sequence; D001191:Arylamine N-Acetyltransferase / Q000235:genetics / Q000378:metabolism*; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009161:Mycobacterium / Q000201:enzymology* / Q000235:genetics; D011110:Polymorphism, Genetic
chemical_list: D001191:Arylamine N-Acetyltransferase