title: Crystal structure of 3-amino-5-hydroxybenzoic acid (AHBA) synthase.
abstract: The biosynthesis of ansamycin antibiotics, including rifamycin B, involves the synthesis of an aromatic precursor, 3-amino-5-hydroxybenzoic acid (AHBA), which serves as starter for the assembly of the antibiotics' polyketide backbone. The terminal enzyme of AHBA formation, AHBA synthase, is a dimeric, pyridoxal 5'-phosphate (PLP) dependent enzyme with pronounced sequence homology to a number of PLP enzymes involved in the biosynthesis of antibiotic sugar moieties. The structure of AHBA synthase from Amycolatopsis mediterranei has been determined to 2.0 A resolution, with bound cofactor, PLP, and in a complex with PLP and an inhibitor (gabaculine). The overall fold of AHBA synthase is similar to that of the aspartate aminotransferase family of PLP-dependent enzymes, with a large domain containing a seven-stranded beta-sheet surrounded by alpha-helices and a smaller domain consisting of a four-stranded antiparallel beta-sheet and four alpha-helices. The uninhibited form of the enzyme shows the cofactor covalently linked to Lys188 in an internal aldimine linkage. On binding the inhibitor, gabaculine, the internal aldimine linkage is broken, and a covalent bond is observed between the cofactor and inhibitor. The active site is composed of residues from two subunits of AHBA synthase, indicating that AHBA synthase is active as a dimer.
authors.affiliation: School of Biochemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
authors.forename: J C
authors.initials: JC
authors.lastname: Eads
authors.forename: M
authors.initials: M
authors.lastname: Beeby
authors.forename: G
authors.initials: G
authors.lastname: Scapin
authors.forename: T W
authors.initials: TW
authors.lastname: Yu
authors.forename: H G
authors.initials: HG
authors.lastname: Floss
mesh_terms: D039903:Actinobacteria / Q000201:enzymology; D001665:Binding Sites; D003198:Computer Simulation; D003460:Crystallization; D018360:Crystallography, X-Ray; D003509:Cyclohexanecarboxylic Acids / Q000737:chemistry / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D006836:Hydro-Lyases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D017510:Protein Folding; D011732:Pyridoxal Phosphate / Q000737:chemistry / Q000378:metabolism
chemical_list: D003509:Cyclohexanecarboxylic Acids; D004791:Enzyme Inhibitors; C012987:gabaculine; D011732:Pyridoxal Phosphate; C111160:3-amino-5-hydroxybenzoic acid synthase; D006836:Hydro-Lyases