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Science. 2007 Jan 19;315(5810):373-7. Epub 2006 Dec 7.

An inward-facing conformation of a putative metal-chelate-type ABC transporter.

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Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, MC 114-96, California Institute of Technology (Caltech), Pasadena, CA 91125, USA.


The crystal structure of a putative metal-chelate-type adenosine triphosphate (ATP)-binding cassette (ABC) transporter encoded by genes HI1470 and HI1471 of Haemophilus influenzae has been solved at 2.4 angstrom resolution. The permeation pathway exhibits an inward-facing conformation, in contrast to the outward-facing state previously observed for the homologous vitamin B12 importer BtuCD. Although the structures of both HI1470/1 and BtuCD have been solved in nucleotide-free states, the pairs of ABC subunits in these two structures differ by a translational shift in the plane of the membrane that coincides with a repositioning of the membrane-spanning subunits. The differences observed between these ABC transporters involve relatively modest rearrangements and may serve as structural models for inward- and outward-facing conformations relevant to the alternating access mechanism of substrate translocation.

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