Binding of Ca2+ to sulfogalactosylceramide and the sequential effects on the lipid dynamics

Sulfogalactosylceramide (SGC) is a sulfoglycolipid commonly found in epithelial cells and most animal germ cells. Its cellular function in sperm is unknown, although it has been implicated in cation transport in epithelial cells. The purpose of this study was to determine the lipid dynamic effects of Ca2+ binding to SGC. High-pressure Fourier transform infrared spectroscopy was used in this study. Our spectral results showed that Ca2+ bound to the sulfate moiety of SGC. Moreover, Ca2+ binding weakened the hydrogen bonding of the polar head region of SGC and the hydrocarbon chains became more disordered as revealed by an increase in the correlation field splitting pressure of SGC. Consequently, Ca2+ binding to SGC would increase the fluidity of SGC multibilayers. However, the presence of an alpha-hydroxyl group on the SGC fatty acid was found to strengthen the hydrogen bonding of the polar head region and as a consequence reduced the Ca(2+)-enhanced hydrocarbon chain disorder. Experimental approaches, described in this paper, serve as a model for further studies of the effects of Ca2+ binding on the dynamics of membranes containing SGC or other sulfatides.