Crystal Structure of the Maltose Transporter in a Pretranslocation Intermediate State

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Science  03 Jun 2011:
Vol. 332, Issue 6034, pp. 1202-1205
DOI: 10.1126/science.1200767

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Adenosine triphosphate (ATP)–binding cassette (ABC) transporters convert chemical energy from ATP hydrolysis to mechanical work for substrate translocation. They function by alternating between two states, exposing the substrate-binding site to either side of the membrane. A key question that remains to be addressed is how substrates initiate the transport cycle. Using x-ray crystallography, we have captured the maltose transporter in an intermediate step between the inward- and outward-facing states. We show that interactions with substrate-loaded maltose-binding protein in the periplasm induce a partial closure of the MalK dimer in the cytoplasm. ATP binding to this conformation then promotes progression to the outward-facing state. These results, interpreted in light of biochemical and functional studies, provide a structural basis to understand allosteric communication in ABC transporters.

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