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Publication Abstract from PubMed

ATP-binding cassette (ABC) transporters are integral membrane proteins that translocate a wide variety of substrates across cellular membranes and are conserved from bacteria to humans. Here we compare four x-ray structures of the bacterial ABC lipid flippase, MsbA, trapped in different conformations, two nucleotide-bound structures and two in the absence of nucleotide. Comparison of the nucleotide-free conformations of MsbA reveals a flexible hinge formed by extracellular loops 2 and 3. This hinge allows the nucleotide-binding domains to disassociate while the ATP-binding half sites remain facing each other. The binding of the nucleotide causes a packing rearrangement of the transmembrane helices and changes the accessibility of the transporter from cytoplasmic (inward) facing to extracellular (outward) facing. The inward and outward openings are mediated by two different sets of transmembrane helix interactions. Altogether, the conformational changes between these structures suggest that large ranges of motion may be required for substrate transport.

Flexibility in the ABC transporter MsbA: Alternating access with a twist.,Ward A, Reyes CL, Yu J, Roth CB, Chang G Proc Natl Acad Sci U S A. 2007 Nov 27;104(48):19005-10. Epub 2007 Nov 16. PMID:18024585^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.