title: Structural basis of Synercid (quinupristin-dalfopristin) resistance in Gram-positive bacterial pathogens.
abstract: Synercid, a new semisynthetic streptogramin-derived antibiotic containing dalfopristin and quinupristin, is used in treatment of life-threatening infections caused by glycopeptide-resistant Enterococcus faecium and other bacterial pathogens. However, dissemination of genes encoding virginiamycin acetyltransferases, enzymes that confer resistance to streptogramins, threatens to limit the medical utility of the quinupristin-dalfopristin combination. Here we present structures of virginiamycin acetyltransferase D (VatD) determined at 1.8 A resolution in the absence of ligands, at 2.8 A resolution bound to dalfopristin, and at 3.0 A resolution in the presence of acetyl-coenzyme A. Dalfopristin is bound by VatD in a similar conformation to that described previously for the streptogramin virginiamycin M1. However, specific interactions with the substrate are altered as a consequence of a conformational change in the pyrollidine ring that is propagated to adjacent constituents of the dalfopristin macrocycle. Inactivation of dalfopristin involves acetyl transfer from acetyl-coenzyme A to the sole (O-18) hydroxy group of the antibiotic that lies close to the side chain of the strictly conserved residue, His-82. Replacement of residue 82 by alanine is accompanied by a fall in specific activity of >105-fold, indicating that the imidazole moiety of His-82 is a major determinant of catalytic rate enhancement by VatD. The structure of the VatD-dalfopristin complex can be used to predict positions where further structural modification of the drug might preclude enzyme binding and thereby circumvent Synercid resistance.
authors.affiliation: Krebs Institute for Biomolecular Sciences, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, United Kingdom.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Kehoe
authors.forename: Jaruwaree
authors.initials: J
authors.lastname: Snidwongse
authors.forename: Patrice
authors.initials: P
authors.lastname: Courvalin
authors.forename: John B
authors.initials: JB
authors.lastname: Rafferty
authors.forename: Iain A
authors.initials: IA
authors.lastname: Murray
mesh_terms: D000123:Acetyltransferases / Q000737:chemistry* / Q000235:genetics*; D000409:Alanine / Q000737:chemistry; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D004351:Drug Resistance; D016984:Enterococcus faecium / Q000472:pathogenicity*; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy*; D006639:Histidine / Q000737:chemistry; D008024:Ligands; D008956:Models, Chemical; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D014769:Virginiamycin / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D008024:Ligands; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; D006639:Histidine; D000123:Acetyltransferases; C477287:virginiamycin acetyltransferase D; D000409:Alanine; C113826:dalfopristin