title: Nikkomycin biosynthesis: formation of a 4-electron oxidation product during turnover of NikD with its physiological substrate.
abstract: Nikkomycins are peptidyl nucleoside antibiotics that act as therapeutic antifungal agents in humans and easily degraded insecticides in agriculture. The nikkomycin peptidyl moiety contains a pyridyl residue derived from L-lysine. The first step in peptidyl biosynthesis is an aminotransferase-catalyzed reaction that converts L-lysine to Delta(1)- or Delta(2)-piperideine-2-carboxylate (P2C). Spectral, chromatographic, and kinetic analyses show that the aerobic reaction of nikD with P2C results in the stoichiometric formation of picolinate, accompanied by the reduction of 2 mol of oxygen to hydrogen peroxide. A high resolution HPLC method, capable of separating picolinate, nicotinate and isonicotinate, was developed and used in product identification. NikD contains 1 mol of covalently bound FAD and exists as a monomer in solution. Reductive and oxidative titrations with dithionite and potassium ferricyanide, respectively, show that FAD is the only redox-active group in nikD. Anaerobic reaction of nikD with 1 mol of P2C results in immediate reduction of enzyme-bound FAD. Because nikD is an obligate 2-electron acceptor, it is proposed that the observed 4-electron oxidation of P2C to picolinate occurs via a mechanism involving two successive nikD-catalyzed 2-electron oxidation steps. In addition to nikkomycins, a nikD-like reaction is implicated in the biosynthesis of an L-lysine-derived pyridyl moiety found in streptogramin group B antibiotics that are used as part of a last resort treatment for severe infections due to gram positive bacteria.
authors.affiliation: Department of Biochemistry, Drexel University, College of Medicine, Philadelphia, Pennsylvania 19102, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Bruckner
authors.forename: Guohua
authors.initials: G
authors.lastname: Zhao
authors.forename: David
authors.initials: D
authors.lastname: Venci
authors.forename: Marilyn Schuman
authors.initials: MS
authors.lastname: Jorns
mesh_terms: D000617:Aminoglycosides / Q000096:biosynthesis* / Q000737:chemistry* / Q000302:isolation & purification; D000935:Antifungal Agents / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004583:Electrons; D005182:Flavin-Adenine Dinucleotide / Q000032:analysis; D008024:Ligands; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry
chemical_list: D000617:Aminoglycosides; D000935:Antifungal Agents; D008024:Ligands; D005182:Flavin-Adenine Dinucleotide; C011952:nikkomycin; D010100:Oxygen