Dynamics of α-helical subdomain rotation in the intact maltose ATP-binding cassette transporter.

ATP-binding cassette (ABC) transporters are powered by a nucleotide-binding domain dimer that opens and closes during cycles of ATP hydrolysis. These domains consist of a RecA-like subdomain and an α-helical subdomain that is specific to the family. Many studies on isolated domains suggest that the helical subdomain ro- tates toward the RecA-like subdomain in response to AlP binding, moving the family signature motif into a favorable position to interact with the nucleotide across the dimer interface. Moreover, the transmembrane domains are docked into a cleft at the interface between these subdomains. suggesting a putative role of the rotation in interdomain communication. Electron paramagnetic resonance spectroscopy was used to study the dynamics of this rotation in the intact Escherichia coil maltose transporter MaIFGK2+. This importer requires a periplasmic maltose-binding protein (MBP) that activates AlP hydrolysis by promoting the closure of the cassette dimer (MalK2). Whereas this rotation occurred during the transport cycle, it required not only trinucleotide, but also MBP, suggesting it is part of a global conformational change in the transporter. Interaction of AMP-PNP-Mg2+ and a MBP that is locked in a closed conformation induced a transition from open MaIK2 to semiopen MalK2 without significant subdomain rotation. Inward rotation of the helical subdomain and complete closure of MaIK2 therefore appear to be coupled to the reorientation of transmembrane helices and the opening of MBP. events that promote transfer of maltose into the transporter. After ATP hydrolysis, the helical subdomain rotates out as MaIK2 opens, resetting the transporter in an inward-facing conformation. [ABSTRACT FROM AUTHOR]