A comparison of physical behaviour amongst four glycosphingolipid families

Abstract

In the general search for information regarding glycosphingolipid behaviour and arrangement in membranes there has arisen the question of whether the answers may be very different for different glycosphingolipid families. We show here that in fact considerable basic similarity exists at least amongst a certain number of families as sensed by a spin label probe covalently attached to the glycosphingolipid fatty acid. This potential for similarity may be as important to take account of as is the clearly demonstrated potential for differences based on headgroup structure (Maggio, B., Albert, J. and Yu, R.K. (1988) Biochim. Biophys. Acta 945, 145–160). The ganglioside, G M1, was examined, as were the neutral species, galactosyl ceramide, lactosyl ceramide, and globoside, in phospholipid bilayers at 2 mol% and 10 mol%. In each case EPR spectra of a spin probe at carbon 16 of the single glycolipid fatty acid chain were compared. This was done for both 18-carbon and 24-carbon species in order to test the phenomenon over the range of common glycosphingolipid fatty acid chain length. The most telling result was that spectra of these four families were identical within experimental error in both rigid gel phase and semi-fluid non-cooperative bilayer matrices as sensed by a nitroxide spin probe near the centre of the membrane hydrophobic interior. No glycolipid family showed a detectable difference in organization either laterally or vertically within the membranes, nor in membrane dynamics. In addition, the membrane phase transition sensed by each family fell within the same narrow range. Freeze-etch visualization of glycolipid lateral distribution was attempted using a variety of native lectins and antibodies as markers. Success was severely limited by low affinity of marker attachment to neutral species; however, where testable, no differences were observed amongst families.