Interaction of Lipoproteins with Heparan Sulfate Proteoglycans and with Lipoprotein Lipase. Studies by Surface Plasmon Resonance Technique

Abstract

Interaction of different classes of lipoproteins with heparan sulfate, heparin, and lipoprotein lipase was studied by a surface plasmon resonance based technique on a BIAcore. The proteoglycans were covalently attached to sensor chips as previously described [Lookene, A., Chevreuil, O., Ostergaard, P., & Olivecrona, G. (1996) Biochemistry 35, 12155-12163]. Binding of all lipoproteins, except for beta-VLDL, to endothelial heparan sulfate was low. Binding of chylomicrons (from rat lymph) and of human VLDL was much increased by the presence of lipoprotein lipase. With human LDL, binding was low in the absence of lipase or at low lipase concentrations. For efficient binding, 2-4 lipase dimers per LDL particle were necessary, indicating cooperativity in the interaction. In contrast, HDL did not bind under any conditions. Heparin had higher binding capacity for lipoproteins than heparan sulfate. This was due to a higher number of binding sites on the heparin chains. Binding of LDL, VLDL, and chylomicrons to heparan sulfate-covered surfaces, both in the presence and in the absence of lipoprotein lipase, was characterized by high values for association rate constants (10(4)-10(5) M(-1) s(-1)) and low values for dissociation rate constants (10(-4)-10(-5) M(-1) s(-1)). In some experiments, rabbit beta-VLDL were directly immobilized to the sensor chips. Binding of lipoprotein lipase to these surfaces was characterized by a very high association rate constant (10(6) M(-1) s(-1)). The dissociation of triacylglycerol-rich lipoproteins was more rapid with catalytically active lipase than with active site-inhibited lipase. It was also markedly increased in the presence of free heparin, suggesting fast exchange kinetics at the surface. Based on that, we propose that lipoproteins are relatively mobile at heparan sulfate covered surfaces. Our study emphasizes the important role of lipoprotein lipase, or molecules with similar properties (apolipoprotein E, hepatic lipase), as mediators for binding of lipoproteins to proteoglycans. It also demonstrates the great potential for the use of biosensors for studies of lipoprotein interactions.