title: The crystal structure of MexR from Pseudomonas aeruginosa in complex with its antirepressor ArmR.
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 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.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada V6T1Z3.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Wilke
authors.forename: Markus
authors.initials: M
authors.lastname: Heller
authors.forename: A Louise
authors.initials: AL
authors.lastname: Creagh
authors.forename: Charles A
authors.initials: CA
authors.lastname: Haynes
authors.forename: Lawrence P
authors.initials: LP
authors.lastname: McIntosh
authors.forename: Keith
authors.initials: K
authors.lastname: Poole
authors.forename: Natalie C J
authors.initials: NC
authors.lastname: Strynadka
mesh_terms: D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D003460:Crystallization; D019281:Dimerization; D017433:Protein Structure, Secondary; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D012097:Repressor Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; C423620:MexR protein, Pseudomonas aeruginosa; D012097:Repressor Proteins