Molecular mechanism of the Escherichia coli maltose transporter

• Three crystal structures of the maltose transporter are analyzed.
• Described the nature of conformational changes in a transport cycle.
• A proposed mechanism explains how ATP hydrolysis is coupled to substrate transport.

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: first, what is the nature of conformational changes in a transport cycle? Second, how does substrate activate ATPase activity? Third, how does ATP hydrolysis enable substrate transport?