The crystal structure of MexR from Pseudomonas aeruginosa in complex with its antirepressor ArmRWilke, M.S., Heller, M., Creagh, A.L., Haynes, C.A., McIntosh, L.P., Poole, K., Strynadka, N.C.J.
(2008) Proc.Natl.Acad.Sci.Usa 105: 14832-14837
- PubMed: 18812515
- DOI: 10.1073/pnas.0805489105
- PubMed Abstract:
The intrinsic antimicrobial resistance of the opportunistic human pathogen Pseudomonas aeruginosa is compounded in mutant strains that overexpress multidrug efflux pumps such as the prominent drug-proton antiporter, MexAB-OprM. The primary regulator ...
The intrinsic antimicrobial resistance of the opportunistic human pathogen Pseudomonas aeruginosa is compounded in mutant strains that overexpress multidrug efflux pumps such as the prominent drug-proton antiporter, MexAB-OprM. The primary regulator of the mexAB-oprM operon is the MarR family repressor, MexR. An additional repressor, NalC, also regulates mexAB-oprM by controlling expression of ArmR, an antirepressor peptide that is hypothesized to prevent the binding of MexR to its cognate DNA operator via an allosteric protein-peptide interaction. To better understand how ArmR modulates MexR, we determined the MexR-binding region of ArmR as its C-terminal 25 residues and solved the crystal structure of MexR in a 2:1 complex with this ArmR fragment at 1.8 A resolution. This structure reveals that the C-terminal residues of ArmR form a kinked alpha-helix, which occupies a pseudosymmetrical and largely hydrophobic binding cavity located at the centre of the MexR dimer. Although the ArmR-binding cavity partially overlaps with the small molecule effector-binding sites of other MarR family members, it possesses a larger and more complex binding surface to accommodate the greater size and specific physicochemical properties of a peptide effector. Comparison with the structure of apo-MexR reveals that ArmR stabilizes a dramatic conformational change that is incompatible with DNA-binding. Thus, this work defines the structural mechanism by which ArmR allosterically derepresses MexR-controlled gene expression in P. aeruginosa and reveals important insights into the regulation of multidrug resistance.
Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada V6T1Z3.