Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 105, Issue 35, Pages 12837-12842Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0803799105
Keywords
catalytic cycle; conformational change; EPR; membrane protein; P-glycoprotein
Categories
Funding
- National Institutes of Health [GM-49261]
- National Biomedical EPR Center [EB001980]
- National Cancer Institute Cancer Center [CA23168]
- Purdue Cancer Center
- Fondation pour la Recherche Medicale
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The maltose transporter MaIFGK(2) of Escherichia coli is a member of the ATP-binding cassette superfamily. A periplasmic maltose-binding protein (MBP) delivers maltose to MaIFGK(2) and stimulates its ATPase activity. Site-directed spin labeling EPR spectroscopy was used to study the opening and closing of the nucleotide-binding interface of MaIFGK(2) during the catalytic cycle. In the intact transporter, closure of the interface coincides not just with the binding of ATP, as seen with isolated nucleotide-binding domains, but requires both MBIP and ATP, implying that MBP stimulates ATPase activity by promoting the closure of the nucleotide-binding interface. After ATIP hydrolysis, with MgADP and MBP bound, the nucleotide-binding interface resides in a semi-open configuration distinct from the fully open configuration seen in the absence of any ligand. We propose that Pi release coincides with the reorientation of transmembrane helices to an inward-facing conformation and the final step of maltose translocation into the cell.
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