The ABC maltose transporter

Abstract

SummaryBacterial 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 across the cytoplasmic membrane to ATP hydrolysis. Although ABC transporters have been studied for more than three decades, the structure of these multicomponent systems is unknown, and the mechanism of transport is not understood. This article reviews one of the most widely studied ABC systems, the maltose transporter of Escherichia coli. A first structural model of the transport channel allows discussion of possible mechanisms of transport. In addition, recent experimental evidence suggests that regulation of gene expression and transport activity is far more complex than expected. History and general properties

Diversity of transport mechanisms: common structural principles

“…The ATPase subunit is associated with membrane subunits. For example, in the maltose permease 28 , MalK is the catalytic subunit and can be purified as a soluble ATPase, and MalF and MalG are separate membrane subunits that form the sugar translocation pathway. Although they do not function as secondary transporters in the absence of MalK, they might have evolved from proteins that did (Fig.…”

Biogenesis of MalF and the MalFGK2 Maltose Transport Complex in Escherichia coli Requires YidC

“…MalF functions in maltose transport as a 1:1:2 complex with the integral inner membrane protein MalG and the peripheral inner membrane protein MalK (19,20). The complex belongs to the ATP-binding cassette (ABC) transporter superfamily.…”

Vanadate-catalyzed photocleavage of the signature motif of an ATP-binding cassette (ABC) transporter

“…The maltose transporter traverses the cytoplasmic membrane of Escherichia coli and has proven to be a useful model system for the study of this family. The transporter (MalFGK 2 ) is a complex made up of two transmembrane subunits, MalF and MalG, and two ATPhydrolyzing subunits, MalK 2 , which are exposed to the cytoplasm (4,5). The ATPase subunit of an ABC transporter contains a nucleotide-binding subdomain similar to that seen in F 1 -ATPase (6), and a helical subdomain unique to ABC transporters resulting from the insertion of approximately 70 aa between the canonical Walker A and Walker B motifs that bind MgATP (7,8).…”