Coupling of remote alternating-access transport mechanisms for protons and substrates in the multidrug efflux pump AcrB

Elife. 2014 Sep 19;3:e03145. doi: 10.7554/eLife.03145.

Abstract

Membrane transporters of the RND superfamily confer multidrug resistance to pathogenic bacteria, and are essential for cholesterol metabolism and embryonic development in humans. We use high-resolution X-ray crystallography and computational methods to delineate the mechanism of the homotrimeric RND-type proton/drug antiporter AcrB, the active component of the major efflux system AcrAB-TolC in Escherichia coli, and one most complex and intriguing membrane transporters known to date. Analysis of wildtype AcrB and four functionally-inactive variants reveals an unprecedented mechanism that involves two remote alternating-access conformational cycles within each protomer, namely one for protons in the transmembrane region and another for drugs in the periplasmic domain, 50 Å apart. Each of these cycles entails two distinct types of collective motions of two structural repeats, coupled by flanking α-helices that project from the membrane. Moreover, we rationalize how the cross-talk among protomers across the trimerization interface might lead to a more kinetically efficient efflux system.

Keywords: E. coli; H+ transport; antibiotic resistance; biochemistry; biophysics; drug resistance; drug transport; efflux pump; mechanistic coupling; structural biology.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Crystallography, X-Ray
  • Drug Resistance, Bacterial*
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / metabolism*
  • Hydrogen-Ion Concentration
  • Kinetics
  • Molecular Dynamics Simulation
  • Multidrug Resistance-Associated Proteins / metabolism*
  • Probability
  • Promoter Regions, Genetic
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protons
  • Software
  • Water / chemistry
  • X-Ray Diffraction

Substances

  • AcrB protein, E coli
  • Escherichia coli Proteins
  • Multidrug Resistance-Associated Proteins
  • Protons
  • Water

Grant support

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.