Molecular mechanism of the Escherichia coli maltose transporter

Abstract

ATP-binding cassette (ABC) transporters are ubiquitous membrane proteins that import and export a large variety of materials across the lipid bilayer. A key question that drives ABC transporter research is how ATP hydrolysis is coupled to substrate translocation. This review uses the maltose transporter of Escherichia coli as a model system to understand the molecular mechanism of ABC importers. X-ray crystallography was used to capture the structures of the maltose transporter in multiple conformations. These structures, interpreted in the light of functional data, are discussed to address the following questions: 1. What is the nature of conformational changes in a transport cycle? 2. How does substrate activate ATPase activity? 3. How does ATP hydrolysis enable substrate transport?

Sequential Action of MalE and Maltose Allows Coupling ATP Hydrolysis to Translocation in the MalFGK2 Transporter

“…Maltose therefore accelerates the release of P i and thereby the ATP turnover cycle (step v). How maltose enters the transporter, how it is released from open-state MalE, and how it triggers the return of MalFG to the inward-facing state remain to be determined; different models are possible (7,23,28,(43)(44)(45)(46). In our current model (Fig.…”

“…Hydrolysis of ATP leads to the dissociation of the NBDs, and thus returns the TMDs to their initial inward-facing conformation. This alternating exposure of the TMDs on either side of the membrane, termed the alternating-access mechanism, allows substrate binding, transport, and release, while preserving membrane impermeability (5)(6)(7)(8).…”

In Vitro Reassembly of the Ribose ATP-binding Cassette Transporter Reveals a Distinct Set of Transport Complexes

“…5 transporters comprise a large superfamily of transmembrane proteins that consists of both exporters and importers (1)(2)(3)(4)(5)(6)(7)(8)(9). ABC exporters are found in all domains of life and transport a variety of substrates, including lipids, peptides, toxins, antibiotics, and chemotherapeutic drugs (2).…”

Asymmetric perturbations of signalling oligomers

“…4). While in ATP-binding cassette (ABC) transporters, a ubiquitous family of primary transporters, AA is achieved by the motion of the two TM domains coupled to the association and dissociation of the two NB domains (Davidson & Maloney, 2007;Hollenstein et al, 2007;Sonne et al, 2007;Chen, 2013), in secondary transporters such as neurotransmitter transporters, isomerisation between an inward-and outward facing state is thought to occur by swapping the conformations of symmetry-related structural domains (Forrest et al, 2008).…”