title: Phosphinothricin tripeptide synthetases in Streptomyces viridochromogenes Tü494.
abstract: The tripeptide backbone of phosphinothricin (PT) tripeptide (PTT), a compound with herbicidal activity from Streptomyces viridochromogenes, is assembled by three stand-alone peptide synthetase modules. The enzyme PhsA (66 kDa) recruits the PT-precursor N-acetyl-demethylphosphinothricin (N-Ac-DMPT), whereas the two alanine residues of PTT are assembled by the enzymes PhsB and PhsC (129 and 119 kDa, respectively). During or after assembly, the N-Ac-DMPT residue in the peptide is converted to PT by methylation and deacetylation. Both phsB and phsC appear to be cotranscribed together with two other genes from a single promoter and they are located at a distance of 20 kb from the gene phsA, encoding PhsA, in the PTT biosynthesis gene cluster of S. viridochromogenes. PhsB and PhsC represent single nonribosomal peptide synthetase elongation modules lacking a thioesterase domain. Gene inactivations, genetic complementations, determinations of substrate specificity of the heterologously produced proteins, and comparison of PhsC sequence with the amino terminus of the alanine-activating nonribosomal peptide synthetase PTTSII from S. viridochromogenes confirmed the role of the two genes in the bialanylation of Ac-DMPT. The lack of an integral thioesterase domain in the PTT assembly system points to product release possibly involving two type II thioesterase genes (the1 and the2) located in the PTT gene cluster alone or in conjunction with an as yet unknown mechanism of product release.
authors.affiliation: Mikrobiologie/Biotechnologie, Eberhard-Karls-Universität Tübingen, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schwartz
authors.forename: Nicolas
authors.initials: N
authors.lastname: Grammel
authors.forename: Eva
authors.initials: E
authors.lastname: Heinzelmann
authors.forename: Ullrich
authors.initials: U
authors.lastname: Keller
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wohlleben
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009943:Organophosphorus Compounds / Q000378:metabolism*; D010453:Peptide Synthases / Q000737:chemistry / Q000235:genetics*; D011401:Promoter Regions, Genetic; D013302:Streptomyces / Q000201:enzymology* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D009943:Organophosphorus Compounds; C003122:bialaphos; D010453:Peptide Synthases; C104385:non-ribosomal peptide synthase