Carbohydrate-mediated regulation of interaction of Vibrio cholerae hemolysin with erythrocyte and phospholipid vesicle.

Vibrio cholerae hemolysin is an extracellular pore-forming monomeric protein with a native molecular weight of about 60,000. In this study, we showed that the hemolysin interacted with immobilized phospholipids and cholesterol and formed oligomers in vesicles constituted from phospholipids alone with a stoichiometry identical to those produced in rabbit erythrocyte membrane. However, the hemolysin bound to glycoproteins with terminal beta1-galactosyl residues and an association constant of 9.4 x 10(7) M(-1) was estimated for the hemolysin-asialofetuin complex by solid phase binding assay. Oligomerization of the hemolysin in lipid bilayer converted the sugar-binding monomer to a lectin with strong carbohydrate-dependent hemagglutinating activity accompanied by inactivation of hemolytic activity and loss in ability to interact with phospholipids. There was no evidence for erythrocyte surface carbohydrates playing an essential role in interaction of the hemolysin with the cell. However, specific glycoproteins inhibited hemolysis of rabbit erythrocytes as well as interaction of the hemolysin with phospholipid. The results suggest (i) V. cholerae hemolysin is a monomer with distinct domains associated with specific binding to carbohydrates and interaction with lipids, (ii) the pore-forming property depends solely on the protein-lipid interaction with no evidence for involvement of sugars, and (iii) specific sugars can down-regulate the ability of the hemolysin to form pores in lipid bilayers.