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The Gate Residue F101 regulates coupling of Na and sugar cotransport in hSGLT1
Author(s) -
hirayama bruce a,
Loo Donald D.F.,
Jiang Xuan,
Wright Ernest M
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.1111.2
Subject(s) - cotransporter , chemistry , biophysics , membrane , extracellular , sugar , stoichiometry , electrochemical gradient , residue (chemistry) , sodium , biochemistry , biology , organic chemistry
Ion‐driven cotransporters use the energy stored in the transmembrane electrochemical gradient to drive the substrate across the membrane. This mechanism enables the substrate to be accumulated in the cell, potentially to concentrations far higher than present in the extracellular milieu. The concentrative power of this system is governed by the magnitude of the electrochemical gradient and the coupling stoichiometry of the cotransporter, i.e., how many ions are cotransported with each substrate. The sodium glucose cotransporter hSGLT1 is tightly coupled, with 2 Na cotransported with each sugar. We have found that mutation of F101, a residue that forms one of the extracellular gates to the sugar binding site to Cys, results in a change in how hSGLT1 ties sugar translocation to Na transport. At low external [NaCl] the coupling stoichiometry remained 2Na:1sugar, but at high [NaCl] the stoichiometry increased to 4Na:1sugar, and was invariant for [sugar] from 0.05 to 3mM, and membrane potentials from −50 to −90mV. Under similar conditions wild‐type coupling remained 2Na:1sugar. This indicates that F101, and potentially other ‘gate’ residues, play a role in the transport mechanism greater than simple barriers. Supported by NIH grant DK 19567.