Low density lipoprotein binding to human platelets: Role of charge and of specific amino acids

Many human and animal cells possess cell surface binding sites, specific for low density lipoproteins. Human platelets are similarly endowed with specific low density lipoprotein receptors. Using chemical modofications of amino acid residues on the low density lipoprotein molecule, we have studied the role of charge and specific amino acids on the binding process. The interaction of the modified low density lipoprotein preparations with gel-filtered platelets and with glass beads was compared. Both cyclohexanedione treated and aceto-acetylated low density lipoprotein did not bind to the platelet surface. However, azo-arsanilated low density lipoprotein bound to the platelets in a manner similar to the binding of native lipoprotein. Cyclohexanedione treated lipoprotein was the only preparation which did not bind to glass beads. The importance of both the presence of the positive charge on the lipoprotein molecule and the availability of specific amino acid residues (arginine and lysine but not tyrosine and histidine) for low density lipoprotein-platelet interaction was thus demonstrated.