Sequential Action of MalE and Maltose Allows Coupling ATP Hydrolysis to Translocation in the MalFGK2 Transporter*

  1. Franck Duong‡3
  1. From the Departments of ‡Biochemistry and Molecular Biology and
  2. §Mathematics, University of British Columbia, Vancouver, British Columbia V6T1Z3, Canada
  1. ↵3 To whom correspondence should be addressed: Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, British Columbia V6T1Z3, Canada. Tel.: 604-822-5975; Fax: 604-822-522; E-mail: fduong{at}mail.ubc.ca

  1. ↵1 Both authors contributed equally to this work.

  • ↵2 Present address: Vancouver Prostate Centre, University of British Columbia, Vancouver, British Columbia V6H 3Z6, Canada.

Background: MalE and maltose together stimulate the ATPase activity of MalFGK2.

Results: Binding of open-state MalE triggers the cleavage of ATP; maltose triggers the release of Pi.

Conclusion: Open-state MalE stabilizes the transporter in the outward-facing conformation; maltose triggers return to the inward-facing state.

Significance: The complementary action of MalE and maltose allows coupling ATP consumption to transport.

Abstract

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.

Footnotes

  • ↵* This work was supported by operating grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Institutes of Health Research (CIHR) (to F. D. and E. C.) and a Four-Year Fellowship from the University of British Columbia (to H. B.). The authors declare that they have no conflicts of interest with the contents of this article.

  • Received June 11, 2015.
  • Revision received August 21, 2015.
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  1. First Published on September 3, 2015 doi: 10.1074/jbc.M115.671826 The Journal of Biological Chemistry 290, 25452-25460.
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