Effect of ganglioside GM3 on the erythrocyte glucose transporter (GLUT1): Conformational changes measured by steady-state and time-resolved fluorescence spectroscopy

Abstract

Interactions between ganglioside GM3 and glucose transporter, GLUT1 were studied by measuring the effect of GM3 on steady-state and time-resolved fluorescence of purified GLUT1 in synthetic lipids and on the 3-O-methylglucose uptake by human erythrocytes. The intrinsic tryptophan fluorescence showed a GLUT 1 emission maximum of 335 nm, and increased in the presence of GM3 by 12% without shifting the emission maximum. The fluorescence lifetimes of intrinsic tryptophan on GLUT1 consisted of a long component of 7.8 ns and a short component of 2.3 ns and GM3 increased both lifetime components. Lifetime components were quenched by acrylamide and KI. Acrylamide-induced quenching of long-lifetime components was partly recovered by GM3. However, KI-induced quenching of short- and long-lifetime components was not rescued by GM3. The anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH)-probed dimyristoylphosphatidylcholine (DMPC) model membrane was also increased with GM3 incorporation. The transport rate of 3-O-methylglucose increased by 20% with GM3 incorporation on the erythrocytes. Therefore, GM3 altered the environment of lipid membrane and induced the conformational change of GLUT1.