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  • Title: Both maltose-binding protein and ATP are required for nucleotide-binding domain closure in the intact maltose ABC transporter.
    Author: Orelle C, Ayvaz T, Everly RM, Klug CS, Davidson AL.
    Journal: Proc Natl Acad Sci U S A; 2008 Sep 02; 105(35):12837-42. PubMed ID: 18725638.
    Abstract:
    The maltose transporter MalFGK(2) of Escherichia coli is a member of the ATP-binding cassette superfamily. A periplasmic maltose-binding protein (MBP) delivers maltose to MalFGK(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 MalFGK(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 MBP and ATP, implying that MBP stimulates ATPase activity by promoting the closure of the nucleotide-binding interface. After ATP 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 P(i) 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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