THE ABC MALTOSE TRANSPORTER

Bacterial ATP-binding cassette (ABC) transporters and their homologues in eukaryotic cells form one of the largest superfamilies known today . They function as primary pumps that couple substrate translocation a cross the cytoplasmic membrane to ATP hydrolysis. Although ABC transpo rters have been studied for more than three decades, the structure of these multicomponent systems is unknown, and the mechanism of transpor t is not understood. This article reviews one of the most widely studi ed ABC systems, the maltose transporter of Escherichia coli, A first s tructural model of the transport channel allows discussion of possible mechanisms of transport. In addition, recent experimental evidence su ggests that regulation of gene expression and transport activity is fa r more complex than expected.