title: Biosynthesis of L-p-hydroxyphenylglycine, a non-proteinogenic amino acid constituent of peptide antibiotics.
abstract: BACKGROUND
  The non-proteinogenic amino acid p-hydroxyphenylglycine is a crucial component of certain peptidic natural products synthesized by a non-ribosomal peptide synthetase mechanism. In particular, for the vancomycin group of antibiotics p-hydroxyphenylglycine plays a structural role in formation of the rigid conformation of the central heptapeptide aglycone in addition to being the site of glycosylation. Initial labeling studies suggested tyrosine was a precursor of p-hydroxyphenylglycine but the specific steps in p-hydroxyphenylglycine biosynthesis remained unknown. Recently, the sequencing of the chloroeremomycin gene cluster from Amycolatopsis orientalis gave new insights into the biosynthetic pathway and allowed for the prediction of a four enzyme pathway leading to L-p-hydroxyphenylglycine from the common metabolite prephenate.
  
  
  RESULTS
  We have characterized three of the four proposed enzymes of the L-p-hydroxyphenylglycine biosynthetic pathway. The three enzymes are encoded by open reading frames (ORFs) 21, 22 and 17 (ORF21: [PCZA361.1, O52791, CAA11761]; ORF22: [PCZA361. 2, O52792, CAA11762]; ORF17: [PCZA361.25, O52815, CAA11790]), of the chloroeremomycin biosynthetic gene cluster and we show they have p-hydroxymandelate synthase, p-hydroxymandelate oxidase and L-p-hydroxyphenylglycine transaminase activities, respectively.
  
  
  CONCLUSIONS
  The L-p-hydroxyphenylglycine biosynthetic pathway shown here is proposed to be the paradigm for how this non-proteinogenic amino acid is synthesized by microorganisms incorporating it into peptidic natural products. This conclusion is supported by the finding of homologs for the four L-p-hydroxyphenylpyruvate biosynthetic enzymes in four organisms known to synthesize peptidic natural products that contain p-hydroxyphenylglycine. Three of the enzymes are proposed to function in a cyclic manner in vivo with L-tyrosine being both the amino donor for L-p-hydroxyphenylglycine and a source of p-hydroxyphenylpyruvate, an intermediate in the biosynthetic pathway.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: B K
authors.initials: BK
authors.lastname: Hubbard
authors.forename: M G
authors.initials: MG
authors.lastname: Thomas
authors.forename: C T
authors.initials: CT
authors.lastname: Walsh
mesh_terms: D000192:Actinomycetales / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000096:biosynthesis* / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005998:Glycine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000737:chemistry; D009097:Multienzyme Complexes / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D005810:Multigene Family / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D013379:Substrate Specificity; D000637:Transaminases / Q000235:genetics / Q000378:metabolism; D014640:Vancomycin / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D009097:Multienzyme Complexes; C112142:chloroeremomycin; D014640:Vancomycin; C023010:4-hydroxyphenylglycine; D000637:Transaminases; D005998:Glycine