A CARBOHYDRATE CARBOHYDRATE INTERACTION BETWEEN GALACTOSYLCERAMIDE-CONTAINING LIPOSOMES AND CEREBROSIDE SULFATE-CONTAINING LIPOSOMES - DEPENDENCE ON THE GLYCOLIPID CERAMIDE COMPOSITION

Galactosylceramide (GalCer) and cerebroside sulfate (CBS) are the majo r glycolipids found in myelin. They occur in greater concentrations in this membrane than any other. Recently, it was reported that these tw o glycolipids can participate in a heterotypic carbohydrate-carbohydra te interaction [Hakomori et al. (1991) Glycoconjugate J. 8,178]. In th e present study, the effect of changes in the ceramide composition of both GalCer and CBS on this interaction has been examined. The interac tion was monitored by measuring the aggregation of small unilamellar p hosphatidylcholine/cholesterol liposomes containing GalCer with simila r liposomes containing CBS, through the increase in optical density at 450 nm. Aggregation depends on the addition of a divalent cation and varies inversely with the ionic radius of the cation. Aggregation occu rred at millimolar concentrations of divalent cation and was inhibited and reversed by the addition of EDTA. A lesser degree of homotypic se lf-aggregation of GalCer and of CBS liposomes also occurred in the pre sence of divalent cations, but the sum of this self-aggregation was si gnificantly less than the heterotypic interaction between the two type s of liposomes. Changes in the ceramide composition of GalCer and CBS significantly affected the extent of their interaction with each other . Increasing the fatty acid chain length of either GalCer or CBS resul ted in increased aggregation. Hydroxylation of the fatty acid also inc reased the degree of aggregation of GalCer and CBS liposomes. These fi ndings indicate that a divalent cation-mediated GalCer-CBS interaction could play a role in cell recognition and membrane adhesion phenomena such as the formation of compact multilamellar myelin. They indicate further that the ceramide composition can influence the receptor activ ity of the carbohydrate head groups of glycolipids, suggesting that va riations in the ceramide composition which occur in myelin in differen t species, during development, and in some diseases could modulate the formation and maintenance of compact myelin.