5] Noncatalytic functions of lipoprotein lipase

Abstract

Publisher Summary Lipoprotein lipase (LPL) is a member of the mammalian triglyceride lipase family. Theoretically, LPL monomers should be able to mediate binding between lipoproteins and heparin/proteoglycans because the binding sites do not interfere with each other as in the case of lipoproteins and low-density receptor-related protein (LRP). However, the affinity for proteoglycans of monomeric LPL is probably too low. Only low amounts of LPL monomers appear to be bound to the vascular endothelium in a heparin-releasable manner. The ability of dimeric LPL to mediate binding of lipoproteins to cell surfaces is due to its high-affinity binding sites for lipids, for proteoglycans, and for LRP. A similar ability has recently been found for hepatic lipase, which also binds both to LRP and to lipoproteins. Furthermore, it binds to heparin and heparin-like proteoglycans but with much lower affinity than LPL. A prerequisite for studies of the noncatalytic function of these lipases is to generate inactive, but conformationally intact or native, forms. The results suggest that blocking of the active site of LPL with specific inhibitors does not induce major conformational changes in the enzyme.