Interaction of cholesterol-crystallization-promoting proteins with vesicles

In this study, the interaction of mucin and concanavalin A-binding proteins isolated from human bile with cholesterol/phospholipid vesicles was investigated. Using resonance energy transfer assays originally developed by Struck, Hoekstra and Pagano [(1981) Biochemistry 20, 4093-4099], no significant protein-induced fusion or aggregation of vesicles was demonstrated. Instead of fusion, these proteins induced destabilization of cholesterol/phospholipid vesicles, as monitored by release of entrapped carboxyfluorescein. A good correlation (rho = 0.81) was obtained between the extent of leakage and the nucleation-promoting activity of the concanavalin A-binding proteins. We conclude that aggregation or fusion of cholesterol/phospholipid vesicles is not an obligatory step in cholesterol crystallization. Biliary protein-induced crystallization seems to be preceded by vesicle disruption.