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Title: Three surface subdomains form the vestibule of the Na<sup>+</sup>/glucose cotransporter SGLT1
Authors: Theeraporn Puntheeranurak
Myriam Kasch
Obing Xia
Peter Hinterdorfer
Rolf K.H. Kinne
Mahidol University
Max Planck Institut fur molekulare Physiologie
Johannes Kepler Universitat Linz
Keywords: Biochemistry, Genetics and Molecular Biology
Issue Date: 31-Aug-2007
Citation: Journal of Biological Chemistry. Vol.282, No.35 (2007), 25222-25230
Abstract: A combination of biophysical and biochemical approaches was employed to probe the topology, arrangement, and function of the large surface subdomains of SGLT1 in living cells. Using atomic force microscopy on the single molecule level, Chinese hamster ovary cells overexpressing SGLT1 were probed with atomic force microscopy tips carrying antibodies against epitopes of different subdomains. Specific single molecule recognition events were observed with antibodies against loop 6-7, loop 8-9, and loop 13-14, demonstrating the extracellular orientation of these subdomains. The addition of D-glucose in Na+-containing medium decreased the binding probability of the loop 8-9 antibody, suggesting a transport-related conformational change in the region between amino acids 339 and 356. Transport studies with mutants C345A, C351A, C355A, or C361S supportedarolefortheseaminoacidsindeterminingtheaffinityof SGLT1 for D-glucose. MTSET, [2-(Trimethylammonium)ethyl] methanethiosulfonate and dithiothreitol inhibition patterns on α-methyl-glucoside uptake by COS-7 cells expressing C255A, C560A, or C608A suggested the presence of a disulfide bridge between Cys255and Cys608. This assumption was corroborated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry showing mass differences in peptides derived from transporters biotinylated in the absence and presence of dithiothreitol. These results indicate that loop 6-7 and loop 13-14 are connected by a disulfide bridge. This bridge brings also loop 8-9 into close vicinity with the former subdomains to create a vestibule for sugar binding. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.
ISSN: 1083351X
Appears in Collections:Scopus 2006-2010

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