title: Multidrug-binding transcription factor QacR binds the bivalent aromatic diamidines DB75 and DB359 in multiple positions.
abstract: Staphylococcus aureus QacR is a multidrug-binding transcription repressor. Crystal structures of multiple QacR-drug complexes reveal that these toxins bind in a large pocket, which is composed of smaller overlapping "minipockets". Stacking, van der Waals, and ionic interactions are common features of binding, whereas hydrogen bonds are limited. Pentamidine, a bivalent aromatic diamidine, interacts with QacR differently as one positively charged benzamidine moiety is neutralized by the dipoles of side-chain and peptide backbone oxygens rather than a formal negative charge from proximal acidic residues. To understand the binding mechanisms of other bivalent benzamidines, we determined the crystal structures of the QacR-DB75 and QacR-DB359 complexes and measured their binding affinities. Although these rigid aromatic diamidines bind with low-micromolar affinities, they do not use single, discrete binding modes. Such promiscuous binding underscores the intrinsic chemical redundancy of the QacR multidrug-binding pocket. Chemical redundancy is likely a hallmark of all multidrug-binding pockets, yet it is utilized by only a subset of drugs, which, for QacR, so far appears to be limited to chemically rigid, bivalent compounds.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas MD Anderson Cancer Center, Unit 1000, Houston, TX 77030, USA.
authors.forename: Benjamin E
authors.initials: BE
authors.lastname: Brooks
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Piro
authors.forename: Richard G
authors.initials: RG
authors.lastname: Brennan
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001550:Benzamidines / Q000737:chemistry* / Q000378:metabolism*; D004925:Escherichia; D005798:Genes, Bacterial; D008958:Models, Molecular; D015394:Molecular Structure; D016296:Mutagenesis; D011485:Protein Binding; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001550:Benzamidines; C523072:DB359; C442128:QacR protein, Staphylococcus aureus; D012097:Repressor Proteins; C033286:furamidine