Antagonistic effect of ganglioside GM1 and GM3 on the activity and conformation of sarcoplasmic reticulum Ca²⁺-ATPase

It was found that rabbit skeletal muscle sarcoplasmic reticulum (SR) contained two main gangliosides: NeuNAcα 2→3 Galβ 1→4 Glcβ 1→1'ceramide (GM3) and Galβ 1→3 GalNAcβ 1→4(NeuNAcα 2→3) Galβ 1→4 Glcβ 1→1'ceramide (GM1), and that the most abundant ganglioside GM3 could positively modulate the SR Ca²⁺-ATPase activity. In this paper, the effect of GM1 on Ca²⁺-ATPase was further investigated and compared with that of GM3. The study demonstrates that GM1 has an opposite effect with respect to GM3 on the activity of SR Ca²⁺-ATPase. Using assays, including intrinsic and time-resolved fluorescence and fluorescence quenching, the conformational changes of SR Ca²⁺-ATPase induced by GM1 and GM3 were compared. Obtained results indicate that GM1 could make the Ca²⁺-ATPase molecules less compact in the hydrophilic domain but more compact in the hydrophobic domain, while GM3 makes the enzyme more compact in both the hydrophilic and hydrophobic domain. Homogeneous GM1 and GM3 with the same ceramide moiety had similar effects on SR Ca²⁺-ATPase activities compared to their natural counterparts, suggesting that the carbohydrate chain may be the key moiety of the ganglioside molecule to be responsible for the difference of the effect on enzyme activity. Copyright (C) 1999 Federation of European Biochemical Societies.