title: 3-Amino-5-hydroxybenzoic acid synthase, the terminal enzyme in the formation of the precursor of mC7N units in rifamycin and related antibiotics.
abstract: The biosynthesis of ansamycin antibiotics, like rifamycin B, involves formation of 3-amino-5-hydroxybenzoic acid (AHBA) by a novel variant of the shikimate pathway. AHBA then serves as the starter unit for the assembly of a polyketide which eventually links back to the amino group of AHBA to form the macrolactam ring. The terminal enzyme of AHBA formation, which catalyzes the aromatization of 5-deoxy-5-amino-3-dehydroshikimic acid, has been purified to homogeneity from Amycolatopsis mediterranei, the encoding gene has been cloned, sequenced, and overexpressed in Escherichia coli. The recombinant enzyme, a (His)6 fusion protein, as well as the native one, are dimers containing one molecule of pyridoxal phosphate per subunit. Mechanistic studies showed that the enzyme-bound pyridoxal phosphate forms a Schiff's base with the amino group of 5-deoxy-5-amino-3-dehydroshikimic acid and catalyzes both an alpha, beta-dehydration and a stereospecific 1,4-enolization of the substrate. Inactivation of the gene encoding AHBA synthase in the A. mediterranei genome results in loss of rifamycin formation; production of the antibiotic is restored when the mutant is supplemented with AHBA.
authors.affiliation: Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA.
authors.forename: C G
authors.initials: CG
authors.lastname: Kim
authors.forename: T W
authors.initials: TW
authors.lastname: Yu
authors.forename: C B
authors.initials: CB
authors.lastname: Fryhle
authors.forename: S
authors.initials: S
authors.lastname: Handa
authors.forename: H G
authors.initials: HG
authors.lastname: Floss
mesh_terms: D039903:Actinobacteria / Q000201:enzymology* / Q000235:genetics; D000192:Actinomycetales / Q000201:enzymology* / Q000235:genetics; D000595:Amino Acid Sequence; D062365:Aminobenzoates / Q000378:metabolism*; D001483:Base Sequence; D003001:Cloning, Molecular; D003509:Cyclohexanecarboxylic Acids / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D019143:Evolution, Molecular; D006836:Hydro-Lyases / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D062385:Hydroxybenzoates; D008969:Molecular Sequence Data; D010802:Phylogeny; D011732:Pyridoxal Phosphate / Q000378:metabolism; D011733:Pyridoxamine / Q000031:analogs & derivatives / Q000378:metabolism; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D015183:Restriction Mapping; D012294:Rifamycins / Q000096:biosynthesis*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012765:Shikimic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity; D000637:Transaminases / Q000145:classification / Q000235:genetics
chemical_list: C111161:5-deoxy-5-amino-3-dehydroshikimic acid; D062365:Aminobenzoates; D003509:Cyclohexanecarboxylic Acids; D062385:Hydroxybenzoates; D011994:Recombinant Proteins; D012294:Rifamycins; D012765:Shikimic Acid; C012987:gabaculine; D011732:Pyridoxal Phosphate; D011733:Pyridoxamine; C031509:3-amino-5-hydroxybenzoic acid; D000637:Transaminases; C111160:3-amino-5-hydroxybenzoic acid synthase; D006836:Hydro-Lyases; C010627:pyridoxamine phosphate