title: Sugar binding induces the same global conformational change in purified LacY as in the native bacterial membrane.
abstract: Many independent lines of evidence indicate that the lactose permease of Escherichia coli (LacY) is highly dynamic and that sugar binding causes closing of a large inward-facing cavity with opening of a wide outward-facing hydrophilic cavity. Therefore, lactose/H(+) symport catalyzed by LacY very likely involves a global conformational change that allows alternating access of single sugar- and H(+)-binding sites to either side of the membrane (the alternating access model). The x-ray crystal structures of LacY, as well as the majority of spectroscopic studies, use purified protein in detergent micelles. By using site-directed alkylation, we now demonstrate that sugar binding induces virtually the same global conformational change in LacY whether the protein is in the native bacterial membrane or is solubilized and purified in detergent. The results also indicate that the x-ray crystal structure reflects the structure of wild-type LacY in the native membrane in the absence of sugar.
authors.affiliation: Department of Physiology, Department of Microbiology, Immunology & Molecular Genetics, and Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA.
authors.forename: Yiling
authors.initials: Y
authors.lastname: Nie
authors.forename: H Ronald
authors.initials: HR
authors.lastname: Kaback
mesh_terms: D050260:Carbohydrate Metabolism; D002241:Carbohydrates; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008823:Micelles; D008958:Models, Molecular; D009004:Monosaccharide Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012995:Solubility; D027981:Symporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D002241:Carbohydrates; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D008823:Micelles; D009004:Monosaccharide Transport Proteins; D027981:Symporters
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