Sequential Action of MalE and Maltose Allows Coupling ATP Hydrolysis to Translocation in the MalFGK2 Transporter.
ATP-binding cassette (ABC) transporters have evolved an ATP-dependent alternating-access mechanism to transport substrates across membranes. Despite important progress, especially in their structural analysis, it is still unknown how the substrate stimulates ATP hydrolysis, the hallmark of ABC transporters. In this study, we measure the ATP turnover cycle of MalFGK2 in steady and pre-steady state conditions. We show that (i) the basal ATPase activity of MalFGK2 is very low because the cleavage of ATP is rate-limiting, (ii) the binding of open-state MalE to the transporter induces ATP cleavage but leaves release of Pi limiting, and (iii) the additional presence of maltose stimulates release of Pi, and therefore increases the overall ATP turnover cycle. We conclude that open-state MalE stabilizes MalFGK2 in the outward-facing conformation until maltose triggers return to the inward-facing state for substrate and Pi release. This concerted action explains why ATPase activity of MalFGK2 depends on maltose, and why MalE is essential for transport.
From the Departments of Biochemistry and Molecular Biology and.
Huan
H
Bao
From the Departments of Biochemistry and Molecular Biology and.
Kush
K
Dalal
Mathematics, University of British Columbia, Vancouver, British Columbia V6T1Z3, Canada.
Eric
E
Cytrynbaum
From the Departments of Biochemistry and Molecular Biology and fduong@mail.ubc.ca.
Franck
F
Duong
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006868:Hydrolysis; D008320:Maltose / Q000378:metabolism*; D033902:Periplasmic Binding Proteins / Q000378:metabolism*
D018528:ATP-Binding Cassette Transporters; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D033902:Periplasmic Binding Proteins; C461599:maltose transport system, E coli; D008320:Maltose; D000255:Adenosine Triphosphate
ABC transporter; ATPase; alternate access; enzyme kinetics; importer; membrane protein; nanodiscs; rapid kinetics; transport