MalFGK2

MalFGK2 is an ATP-binding cassette (ABC) transporter that mediates the uptake of maltose and maltodextrins across the inner membrane of many enteric bacteria, notably Escherichia coli. The functional transporter comprises the transmembrane subunits MalF and MalG, which form the substrate–holding channel, and a dimer of the cytoplasmic ATPase MalK2 that powers transport. The periplasmic binding protein MalE binds maltose or maltodextrins and delivers them to the transporter. The designation MalFGK2 reflects the dimeric state of MalK within the complex.

Operation begins when MalE-bound maltodextrin docks at MalFGK2, triggering ATP binding and hydrolysis at the MalK dimer. Energy from ATP hydrolysis induces conformational changes that move the sugar through the channel into the cytoplasm, a mechanism typical of type II ABC importers with an alternating access model. The system can transport maltose and a range of maltodextrins, and its efficiency is enhanced by the binding protein MalE.

Genes encoding the maltose transport apparatus form the maltose regulon, including malE, malF, malG, and malK. Expression is induced in the presence of maltose or maltodextrins via the transcriptional activator MalT, coordinating uptake with nutritional availability. Regulation integrates with broader carbon catabolite control in the cell.

MalFGK2 is a well-studied model of prokaryotic ABC importers, illustrating periplasmic binding protein–dependent transport and ATP-driven substrate translocation. Structural and biochemical analyses have detailed the interactions among MalE, MalF, MalG, and the MalK dimer, informing understanding of energy coupling in ABC transporters.