title: Mutational analysis of potential zinc-binding residues in the active site of the enterococcal D-Ala-D-Ala dipeptidase VanX.
abstract: VanX, one of the five proteins required for the vancomycin-resistant phenotype in clinically pathogenic Enterococci, is a zinc-containing d-Ala-d-Ala dipeptidase. To identify potential zinc ligands and begin defining the active site residues, we have mutated the 2 cysteine, 5 histidine, and 4 of the 28 aspartate and glutamate residues in the 202 residue VanX protein. Of 10 mutations, 3 cause inactivation and greater than 90% loss of zinc in purified enzyme samples, implicating His116, Asp123, and His184 as zinc-coordinating residues. Homology searches using the 10 amino acid sequence SxHxxGxAxD, in which histidine and aspartate residues are putative zinc ligands, identified the metal coordinating ligands in the N-terminal domain of the murine Sonic hedgehog protein, which also exhibits an architecture for metal coordination identical to that observed in thermolysin from Bacillus thermoproteolyticus. Furthermore, this 10 amino acid consensus sequence is found in the Streptomyces albus G zinc-dependent N-acyl-d-Ala-d-Ala carboxypeptidase, an enzyme catalyzing essentially the same d-Ala-d-Ala dipeptide bond cleavage as VanX, suggesting equivalent mechanisms and zinc catalytic site architectures. VanX residue Glu181 is analogous to the Glu143 catalytic base in B. thermoproteolyticus thermolysin, and the E181A VanX mutant has no detectable dipeptidase activity, yet maintains near-stoichiometric zinc content, a result consistent with the participation of the residue as a catalytic base.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: McCafferty
authors.forename: I A
authors.initials: IA
authors.lastname: Lessard
authors.forename: C T
authors.initials: CT
authors.lastname: Walsh
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics; D002942:Circular Dichroism; D017124:Conserved Sequence; D004252:DNA Mutational Analysis; D004150:Dipeptidases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016983:Enterococcus / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D007700:Kinetics; D058619:Maltose-Binding Proteins; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase; D013820:Thermolysin / Q000737:chemistry; D013917:Thrombin / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D011993:Recombinant Fusion Proteins; C461599:maltose transport system, E coli; D004150:Dipeptidases; D046929:Serine-Type D-Ala-D-Ala Carboxypeptidase; C091956:VanX dipeptidase; D013917:Thrombin; D013820:Thermolysin; D015032:Zinc