Segments in the C-terminal folding domain of lipoprotein lipase important for binding to the low density lipoprotein receptor-related protein and to heparan sulfate proteoglycans

Lipoprotein lipase (LpL) can mediate cellular uptake of chylomicron and VLDL remnants via binding to heparan sulfate proteoglycans (HSPG) and the endocytic α₂-macroglobulin receptor/low density lipoprotein receptor- related protein (α₂MR/LRP). Whereas it is established that the C-terminal folding domain binds to α₂MR/LRP, it remains uncertain whether it binds to heparin and to HSPG. To identify segments important for binding to α₂MR/LRP and to clarify possible binding to heparin, we produced constructs of the human C-terminal folding domain, LpL-(313-448), and of the fragment LpL- (347-448) in Escherichia coli. In addition to binding to α₂MR/LRP, LpL- (313-448) displayed binding to heparin with an affinity similar to that of the LpL monomer, whereas it bound poorly to lipoprotein particles. Moreover, LpL-(313-448) displayed heparin sensitive binding to normal, but not to HSPG deficient Chinese hamster ovary cells. LpL-(313-448) and LpL-(347-448) showed similar affinities for binding to both purified α₂MR/LRP and to heparin. Deletion of LpL residues 380-384 abolished the binding to LRP, whereas binding to heparin was unperturbed. The binding to both heparin and α₂MR/LRP was essentially abolished following deletion of residues 404-430, and pretreatment of CHO cells with the peptide comprising aa 402-423 inhibited the binding of LpL-(313-448). We conclude that the C-terminal folding domain of human LpL has a site for binding to heparin and to HSPG, presumably involving amino acids within residues 404-430. Two segments of the domain are necessary for efficient binding to α₂MR/LRP, one comprising residues 380-384 and another overlapping the segment important for binding to heparin.