Details

Autor(en) / Beteiligte

• Gagnon, Dominique G.
• Frindel, Carole
• Lapointe, Jean-Yves

Titel

Voltage-Clamp Fluorometry in the Local Environment of the C255–C511 Disulfide Bridge of the Na +/Glucose Cotransporter

Ist Teil von

• Biophysical journal, 2007-04, Vol.92 (7), p.2403-2411

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2007

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• We recently identified a functionally important disulfide bridge between C255 and C511 of the human Na +/glucose cotransporter SGLT1. In this study, voltage-clamp fluorometry was used to characterize the fluorescence of four different dyes attached to C255 and C511 under various ionic and substrate/inhibitor conditions. State-dependent fluorescence changes (Δ F) were observed when TMR5M or TMR6M dyes were attached to C255 and C511 or when Alexa488 was bound to C511. TMR5M-C511 was extremely sensitive to membrane potential ( V m) and to external Na + and αMG (a nonmetabolizable glucose analog) concentrations. A progressive increase in αMG concentration drastically changed the maximal voltage-dependent Δ F and produced a positive shift in the midpoint of the Δ F- V m curve. By determining specific fluorescence intensity for each state of the cotransporter, our steady-state fluorescence data could be reproduced using the rate constants previously proposed for a five-state kinetic model exclusively derived from electrophysiological measurements. Our results bring an independent support to the proposed kinetic model and show that the binding of αMG substrate significantly modifies the environment of C255 and C511.