Promiscuous partnering and independent activity of MexB, the multidrug transporter protein from Pseudomonas aeruginosa.
Résumé
The MexAB-OprM drug efflux pump is central to multidrug resistance of Pseudomonas aeruginosa. The ability of the tripartite protein to confer drug resistance to the pathogen is crucially dependent on the presence of all three proteins of the complex. However, the role of each protein in formation of the intact functional complex is not well understood. One of the key questions relates to the (in)ability of MexB to act independently of its cognitive partners, MexA and OprM. Here we demonstrate that in the absence of MexA and OprM, MexB can (i) recruit AcrA and TolC from E. coli to form a functional drug efflux complex, (ii) transport the toxic compound ethidium in a gram-positive organism where the periplasmic space and outer membrane are absent, and (iii) catalyse transmembrane chemical proton gradient (DpH)-dependent drug transport when purified and reconstituted into proteoliposomes. Our results represent the first evidence for drug transport by an isolated RND type multidrug transporter, and provide a basis for further studies into the energetics of RND-type transporters and their assembly into multiprotein complexes.
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