Binding Protein-Dependent Uptake of Maltose into Cells via an ATP-Binding Cassette Transporter

Maltose and maltodextrins are actively transported across the cytoplasmic membrane of Escherichia coli and Salmonella by a periplasmic binding protein (BP)- dependent transport system. Since 1996, there have been many advances in the understanding of the structure and mechanism of the maltose transporter, in the assembly of the membrane-associated transporter complex, and in the mechanism of regulation of transport both at the DNA and the protein level. The transporter has been studied in detergent and reconstituted in liposome vesicles, and while many features, including the ability of maltose-binding protein (MBP) to stimulate ATPase activity, are retained in detergent, it has been noted that the basal ATPase activity of the transporter is elevated in detergent compared with liposomes. This review focuses on these recent developments, which have culminated in a high resolution structure of MBP in a complex with the MalFGK2 transporter. While this review focuses on the maltose system, complementary work has been carried out on many different ATP binding cassette (ABC) transporters, all of which has contributed in important ways to the understanding of the maltose transport system. The regulation of the maltose transport system, at the DNA level, is implemented by the synergistic action of MalT and cAMP/CAP complex and, at the protein level, by interactions of MalK with unphosphorylated EIIAglc, a signal-transducing component of the phosphoenolpyruvate-glucose phosphotransferase system.