Mechanistic study of modulation of SR Ca2+-ATPpase activity by gangliosides GM1 and GM3 through some biophysical measurements.

On the basis of confirming the antagonistic effects of GM1 and GM3 on the activity of Ca2+-ATPase, we further demonstrated that some of the components of these two gangliosides, including sialic acid (NeuNAc), asialo-GM1, asialo-GM3 and ceramide, failed to show any effects on the activity of Ca2+-ATPase. Thus it is apparent that the intact molecules of these two gangliosides with their specific conformations were needed to perform their effects on Ca2+-ATPase. From the fluorescence resonance energy transfer measurements, the energy transfer between Cys 670/674 and Lys 515 was decreased by GM1 and increased by GM3, indicating GM1 induced the conformation of the hydrophilic region of Ca2+-ATPase to be less compact, while GM3 induced it to be more compact. From the CD spectra measurements, GM1 and GM3 both reduced the content of alpha-helical structures of Ca2+-ATPase, but GM1 caused a stronger decrease than that of GM3. Using DPH as the probe, we found that the membrane lipid fluidity of the proteoliposomes containing Ca2+-ATPase was decreased by GM1 and tend to increase by GM3.