title: Gene vanXYC encodes D,D -dipeptidase (VanX) and D,D-carboxypeptidase (VanY) activities in vancomycin-resistant Enterococcus gallinarum BM4174.
abstract: VanX and VanY have strict D,D-dipeptidase and D,D-carboxypeptidase activity, respectively, that eliminates production of peptidoglycan precursors ending in D-alanyl-D-alanine (D-Ala-D-Ala) in glycopeptide-resistant enterococci in which the C-terminal D-Ala residue has been replaced by D-lactate. Enterococcus gallinarum BM4174 synthesizes peptidoglycan precursors ending in D-Ala-D-serine (D-Ala-D-Ser) essential for VanC-type vancomycin resistance. Insertional inactivation of the vanC-1 gene encoding the ligase that catalyses synthesis of D-Ala-D-Ser has a polar effect on both D, D-dipeptidase and D,D-carboxypeptidase activities. The open reading frame downstream from vanC-1 encoded a soluble protein designated VanXYC (Mr 22 318), which had both of these activities. It had 39% identity and 74% similarity to VanY in an overlap of 158 amino acids, and contained consensus sequences for binding zinc, stabilizing the binding of substrate and catalysing hydrolysis that are present in both VanX- and VanY-type enzymes. It had very low dipeptidase activity against D-Ala-D-Ser, unlike VanX, and no activity against UDP-MurNAc-pentapeptide[D-Ser], unlike VanY. The introduction of plasmid pAT708(vanC-1,XYC) or pAT717(vanXYC) into vancomycin-susceptible Enterococcus faecalis JH2-2 conferred low-level vancomycin resistance only when D-Ser was present in the growth medium. The peptidoglycan precursor profiles of E. faecalis JH2-2 and JH2-2(pAT708) and JH2-2(pAT717) indicated that the function of VanXYC was hydrolysis of D-Ala-D-Ala and removal of D-Ala from UDP-MurNAc-pentapeptide[D-Ala]. VanC-1 and VanXYC were essential, but not sufficient, for vancomycin resistance.
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK. per@mole.bio.cam.ac.uk
authors.forename: P E
authors.initials: PE
authors.lastname: Reynolds
authors.forename: C A
authors.initials: CA
authors.lastname: Arias
authors.forename: P
authors.initials: P
authors.lastname: Courvalin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002268:Carboxypeptidases; D003001:Cloning, Molecular; D004352:Drug Resistance, Microbial / Q000235:genetics; D016983:Enterococcus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D013293:Enterococcus faecalis / Q000235:genetics / Q000378:metabolism; D005798:Genes, Bacterial / Q000235:genetics; D008565:Membrane Proteins; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010457:Peptidoglycan / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase; D013379:Substrate Specificity; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D008565:Membrane Proteins; D010457:Peptidoglycan; C079914:VanC protein, Bacteria; D014640:Vancomycin; D002268:Carboxypeptidases; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase; C117912:VanY protein, Bacteria; C091956:VanX dipeptidase