Assessing the cluster glycoside effect during the binding of concanavalin A to mannosylated artificial lipid rafts.

Mannosyl glycolipids with perfluoroalkyl membrane anchors have been synthesised. When inserted into vesicles, these mannosyl lipids either dispersed evenly over the surface or, in the presence of cholesterol, phase-separated into artificial lipid rafts. At 1% mol/mol, the affinity of dispersed mannosyl lipids for Con A was 3-fold weaker than in solution, perhaps reflecting steric blocking by the surface. However increasing membrane loading 5-fold increased Con A affinity by up to 75% and indicated weak intramembrane chelation of Con A. Despite this observation, concentrating the mannosyl lipids into artificial lipid rafts did not significantly improve affinity for Con A. This lack of a cluster glycoside effect was ascribed to lipid congestion inhibiting intra-raft chelation of Con A, and implies that glycolipids located in lipid rafts may not necessarily be preorganised for multivalent binding.