National Center for
4U8V: Coupling Of Remote Alternating-access Transport Mechanisms For Protons And Substrates In The Multidrug Efflux Pump Acrb
Coupling of remote alternating-access transport mechanisms for protons and substrates in the multidrug efflux pump AcrB
Elife (2014) 3
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 A apart. Each of these cycles entails two distinct types of collective motions of two structural repeats, coupled by flanking alpha-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.