INTERACTION OF LIPOPROTEINS WITH HEPARAN-SULFATE PROTEOGLYCANS AND WITH LIPOPROTEIN-LIPASE - STUDIES BY SURFACE-PLASMON RESONANCE TECHNIQUE

Interaction of different classes of lipoproteins with heparan sulfate, heparin. and lipoprotein lipase was studied by a surface plasmon reso nance based technique on a BIAcore. The proteoglycans were covalently attached to sensor chips as previously described [Lookene, A., Chevreu il, O., Ostergaard, P., & Olivecrona, G. (1996) Biochemistry 35, 12155 -12163]. Binding of all lipoproteins, except for beta-VLDL, to endothe lial heparan sulfate was low. Binding of chylomicrons (from rat lymph) and of human VLDL was much increased by the presence of lipoprotein l ipase. With human LDL, binding was low in the absence of lipase or at low lipase concentrations. For efficient binding, 2-4 lipase dimers pe r LDL particle were necessary, indicating cooperativity in the interac tion. In contrast, HDL did not bind under any conditions. Heparin had higher binding capacity for lipoproteins than heparan sulfate. This wa s due to a higher number of binding sites on the heparin chains. Bindi ng of LDL, VLDL, and chylomicrons to heparan sulfate-covered surfaces, both in the presence and in the absence of lipoprotein lipase, was ch aracterized 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 im mobilized to the sensor chips. Binding of lipoprotein lipase to these surfaces was characterized by a very high association rate constant (1 0(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 f ree heparin, suggesting fast exchange kinetics at the surface. Based o n that, we propose that lipoproteins are relatively mobile at heparan sulfate covered surfaces. Our study emphasizes the important role of l ipoprotein lipase, or molecules with similar properties (apolipoprotei n E, hepatic lipase), as mediators for binding of lipoproteins to prot eoglycans. It also demonstrates the great potential for the use of bio sensors for studies of lipoprotein interactions.