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Proc Natl Acad Sci U S A. 2001 Feb 13;98(4):1525-30. Epub 2001 Feb 6.

Trapping the transition state of an ATP-binding cassette transporter: evidence for a concerted mechanism of maltose transport.

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  • 1Howard Hughes Medical Institute, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.

Abstract

High-affinity uptake into bacterial cells is mediated by a large class of periplasmic binding protein-dependent transport systems, members of the ATP-binding cassette superfamily. In the maltose transport system of Escherichia coli, the periplasmic maltose-binding protein binds its substrate maltose with high affinity and, in addition, stimulates the ATPase activity of the membrane-associated transporter when maltose is present. Vanadate inhibits maltose transport by trapping ADP in one of the two nucleotide-binding sites of the membrane transporter immediately after ATP hydrolysis, consistent with its ability to mimic the transition state of the gamma-phosphate of ATP during hydrolysis. Here we report that the maltose-binding protein becomes tightly associated with the membrane transporter in the presence of vanadate and simultaneously loses its high affinity for maltose. These results suggest a general model explaining how ATP hydrolysis is coupled to substrate transport in which a binding protein stimulates the ATPase activity of its cognate transporter by stabilizing the transition state.

PMID:
11171984
[PubMed - indexed for MEDLINE]
PMCID:
PMC29290
Free PMC Article

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