Antibiotic export by MexB multidrug efflux transporter is allosterically controlled by a MexA-OprM chaperone-like complex

Marie Glavier,Dimitri Salvador,Jean-Christophe Taveau,Martin Picard,Guy Schoehn,Quentin Cece,Isabelle Broutin,Marion Decossas,Laetitia Daury,Cyril Garnier,Dhenesh Puvanendran,Gilles Phan,Olivier Lambert,Elisa Frezza

doi:10.1038/s41467-020-18770-5

Abstract

The tripartite multidrug efflux system MexAB-OprM is a major actor in Pseudomonas aeruginosa antibiotic resistance by exporting a large variety of antimicrobial compounds. Crystal structures of MexB and of its Escherichia coli homolog AcrB had revealed asymmetric trimers depicting a directional drug pathway by a conformational interconversion (from Loose and Tight binding pockets to Open gate (LTO) for drug exit). It remains unclear how MexB acquires its LTO form. Here by performing functional and cryo-EM structural investigations of MexB at various stages of the assembly process, we unveil that MexB inserted in lipid membrane is not set for active transport because it displays an inactive LTC form with a Closed exit gate. In the tripartite complex, OprM and MexA form a corset-like platform that converts MexB into the active form. Our findings shed new light on the resistance nodulation cell division (RND) cognate partners which act as allosteric factors eliciting the functional drug extrusion.

Highlights

The tripartite multidrug efflux system MexAB-OprM is a major actor in Pseudomonas aeruginosa antibiotic resistance by exporting a large variety of antimicrobial compounds
6 Université Grenoble Alpes, CNRS, CEA, Institute for Structural Biology (IBS), 38000 Grenoble, France. 7These authors contributed : Marie Glavier, Dhenesh Puvanendran, Dimitri Salvador. 8These authors jointly supervised this work: Laetitia Daury, Isabelle Broutin, Olivier Lambert. ✉email: isabelle.broutin@parisdescartes.fr; o.lambert@cbmn.u-bordeaux.fr In Gram-negative bacteria, tripartite multidrug efflux systems export biological metabolites and antimicrobial compounds, thereby contributing to bacterial resistance, which emerges as a major health concern[1,2]
Division (RND) superfamily are composed of an inner-membrane resistance nodulation cell division (RND) transporter driven by the proton motive force, an outermembrane factor (OMF), and a periplasmic membrane fusion protein (MFP), forming a tripartite pump with a contiguous exit duct[4,5,6]

Summary

Introduction

The tripartite multidrug efflux system MexAB-OprM is a major actor in Pseudomonas aeruginosa antibiotic resistance by exporting a large variety of antimicrobial compounds. Crystal structures of MexB and of its Escherichia coli homolog AcrB had revealed asymmetric trimers depicting a directional drug pathway by a conformational interconversion (from Loose and Tight binding pockets to Open gate (LTO) for drug exit). It remains unclear how MexB acquires its LTO form. From the asymmetric AcrB structures, a model for a directional drug transport based on conformational cycling of the monomers (referred as functionally rotating mechanism) by utilizing proton binding and dissociation has been proposed with the substrate entry happening in the L monomer, followed by a conformational change to the T monomer resulting in the substrate binding to the binding pocket and the substrate release arose after T monomer conversion to the O monomer. From L to T, T to O, and O to L) and on a common cycling mechanism of RND drug transport

Methods

Results

Conclusion