Ganglioside GM3 modulates conformation of reconstituted Ca(2+)-ATPase

Using steady-state fluorescence and nanosecond time-resolved fluorescence techniques, the Ca(2+) 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 Ca(2+)-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(3V)) 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 Ca(2+)-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.