Abstract
Lipoprotein lipase (LPL) causes a marked increase in the cellular binding of beta-migrating very low density lipoprotein (beta-VLDL) to a large receptor compatible with the alpha 2-macroglobulin receptor (alpha 2MR)/low density lipoprotein receptor-related protein (LRP) (Beisiegel, U., Weber, W., and Bengtsson-Olivecrona, G. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 8342-8346). Here we demonstrate that LPL binds to the alpha-chain of purified alpha 2MR/LRP immobilized on microtiter plates. The binding, apparently to multiple sites, was blocked by heparin and inhibited by the alpha 2MR-associated protein (alpha 2MRAP) and by EDTA. Immobilized LPL bound alpha 2MR/LRP in solution as well as beta-VLDL prepared from cholesterol-fed rabbits. Both binding reactions were dependent on an intact carboxyl-terminal folding domain of LPL, but were independent of its dimeric structure and intact catalytical function. Dimeric LPL could mediate binding of beta-VLDL to immobilized alpha 2MR/LRP and to cells, e.g. monocytes. In contrast, LPL monomers were not able to mediate binding to immobilized alpha 2MR/LRP, presumably because of cross-inhibition due to close relation between the binding regions for the lipoprotein and for the receptor in the carboxyl-terminal domain of the LPL monomer. Heparin, but not alpha 2MRAP, inhibited cellular binding of 125I-LPL or 125I-beta-VLDL supplemented with LPL. However, alpha 2MRAP inhibited degradation of the two ligands by about 90% and 40-50%, respectively. The results show that LPL is a ligand for alpha 2MR/LRP and, because of its affinity for lipoprotein particles, dimeric LPL can mediate or strengthen binding of beta-VLDL to this receptor. It is proposed that LPL binds primarily to cell surface heparan sulfate in monocytes and is presented for endocytosis and degradation by alpha 2MR/LRP. Moreover, beta-VLDL may be further supplemented with LPL at the cell surface and achieve affinity for alpha 2MR/LRP.
Highlights
Lipoprotein (B-VLDL) to a large receptor compatible 1-3)
Dimeric LPL effectively inhibited by active site inhibitors like tetrahydrocould mediatebinding ojf3-VLDL to immobilized lipstatin (THL)
‘“I-LPL or lZ6I-&VLDL supplemented with LPL. shown that LPL binds to cell surfaces
Summary
Fig. 1shows that binding of 1251-a~M-methylamine to purified two-chain a2MR/LRP wasblocked by a2-. ApM-methylamine cell-association (binding anduptake) in a human monocytes at 37 "C.LPL inhibited the degradation of 1251-azM-methylaminien thesecells (Fig.2B). The inset shows that biotin-LPL bound (10 units/ml), EDTA (10 mM), a2MRAP (100 nM), or a2M-methylamine (100nM). SDS-PAGE-resolved a,MR/LRP was electroblotted and incubated with 5 nM biotin-labeled LPL in the absence (-) or presence (+) of heparin (10 units/ml) followedby incubation with alkaline phosphatase-conjugated streptavidin. The maximal binding suggested the presence of multiple LPL binding sites (approximately four, cf legend to Fig. 4) This is supported by the result of experiments in which LPL was.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
