Ganglioside GM3 modulates conformation of reconstituted Ca²⁺-ATPase

Using steady-state fluorescence and nanosecond time-resolved fluorescence techniques, the Ca²⁺-ATPase conformational changes induced by ganglioside GM3 were studied with different quenchers. The results showed that GM3 could significantly increase the lifetime of intrinsic fluorescence of Ca²⁺ -ATPase reconstituted into proteoliposomes, and could also weaken the intrinsic fluorescence quenching by KI or hypocrellin B, HB. Furthermore, by using quenching kinetic analysis of the time-resolved fluorescence, in the presence of GM3, the quenching constant (K_sv) and quenching efficiency were significantly lowered. The obtained results suggest that the oligosaccharide chain and the ceramide moieties of the GM3 molecule could interact with its counterparts of the Ca²⁺ -ATPase respectively, thus change the conformation of the hydrophobic domain of the enzyme, making the tryptophan residues in different regions shift towards the hydrophilic-hydrophobic interface, and hence shorten the distance between the hydrophilic and the hydrophobic domains, making the enzyme with a more compact form exhibit higher enzyme activity.