Population shift disengages DNA binding in a multidrug resistance MexR mutant
(English)Manuscript (preprint) (Other academic)
The homodimeric MexR protein, featuring a MarR helical dimer fold with two DNA-binding wHTH domains, functions as a repressor of the MexAB-OprM multidrug efflux pump operon of Pseudomonas aeruginosa. Mutations in MexR lead to multidrug resistance (MDR) by impairing MexR-directed repression of the efflux operon. In this study, we present the crystal structure of MexR mutant R21W at a resolution of 2.19 Å, together with an evaluation of MexR-wt and -R21W protein dynamics using molecular dynamics simulations. While the crystal structure MexR-R21W is closely similar to that of MexR-wt, our molecular simulations show that the mutant protein only accesses a subset of the conformational space available to the wt protein. Specifically, the R21W mutation results in the coupling of distinct allosteric contact networks that are independent in MexR-wt, effectively leading to reduced independent mobility of wHTH domains relative to the dimerization domain in the mutated protein. Experimental small-angle X-ray scattering in solution independently support a larger structural envelope than the crystal structure for both proteins, and more so for MexR-wt than for MexR-R21W. Taken together, our results suggest that the MexR-R21W mutation disengages DNA binding through population shift, and that this mimics the derepression effected by small-molecule binding to MarR proteins that confers antibiotics resistance. While this view contrasts the previously proposed structure-based cascade of rigid-body rotations that would lead to derepression in the MarR family, our population shift model is in full agreement with previously published data and may well be present also for other MarR proteins.
Chemical Sciences Biochemistry and Molecular Biology
IdentifiersURN: urn:nbn:se:liu:diva-122465OAI: oai:DiVA.org:liu-122465DiVA: diva2:866604