Interactions of the QacR multidrug-binding protein with structurally diverse ligands: Implications for the evolution of the binding pocket

被引:65
作者
Grkovic, S [1 ]
Hardie, KM [1 ]
Brown, MH [1 ]
Skurray, RA [1 ]
机构
[1] Univ Sydney, Sch Biol Sci, Sydney, NSW 2006, Australia
关键词
D O I
10.1021/bi035447+
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The QacR multidrug-binding repressor protein regulates the expression of the Staphylococcus aureus qacA gene, a multidrug resistance (MDR) locus that is prevalent in clinical isolates of this important human pathogen. In this paper we demonstrate that the range of structurally diverse compounds capable of inducing qacA transcription is significantly more varied than previously appreciated, particularly in relation to bivalent cations. For all of the newly identified inducing compounds, induction of qacA expression was correlated with a matching ability to dissociate QacR from operator DNA. Development of a ligand-binding assay based on intrinsic tryptophan fluorescence permitted dissociation constants to be determined for the majority of known QacR ligands, with values ranging from 0.2 to 82 muM. High-affinity binding of a compound to QacR in vitro was not found to correlate very strongly with either its in vivo inducing abilities or its structure. The latter observation indicated that the QacR ligand-binding pocket appears to have evolved to accommodate a wide range of toxic hydrophobic cations, rather than a specific class of compound. Importantly, the antimicrobial ligands of QacR included several plant alkaloids that share structural similarities with synthetic MDR substrates. This is consistent with the suggestion that the qacA-qacR MDR locus was recently derived from genes that protect against natural antimicrobial compounds.
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页码:15226 / 15236
页数:11
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