Effect of apolipoprotein C-I peptides on the apolipoprotein E content and receptor-binding properties of beta-migrating very low density lipoproteins.
To evaluate the role of apolipoprotein (apo) C-I in inhibiting lipoprotein binding to the low density lipoprotein receptor-related protein (LRP), a putative lipoprotein remnant receptor, apoC-peptide fragments were prepared by chemical synthesis or by cyanogen bromide cleavage of intact apoC-I. In ligand-blotting assays, peptides corresponding to residues 1-38, 10-57, 20-57, 30-57, and 40-57 proved ineffective, but intact apoC-I was very effective, at inhibiting the binding of apoE-enriched beta-migrating very low density lipoproteins (beta-VLDL) to the LRP. Studies of the displacement of 125I-labeled apoE from apoE-enriched beta-VLDL showed that the largest peptide (residues 10-57) was two-thirds as effective as intact apoC-I; the other peptides were highly ineffective (residues 40-57, 1-38) or only partly effective (residues 20-57, 30-57). Changes in the intrinsic tryptophan fluorescence and helix content indicated that the largest peptide was similar to apoC-I in lipid binding affinity, while the other peptide fragments showed little or no affinity for either unilamellar or multilamellar vesicles of dimyristoyl-phosphatidylcholine. These findings suggest that the ability of apoC-I fragments to displace apoE from beta-VLDL is largely, but perhaps not exclusively, a reflection of their ability to bind to membranous bilayers and that apoC-I blocking of the interaction between apoE-rich beta-VLDL and the LRP probably involves displacement of a critical amount of the apoE from the surface of this lipoprotein.
Swaney
J B
JB
Department of Biological Chemistry, Hahnemann University, Philadelphia, PA 19102.
Weisgraber
K H
KH
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D053302:Apolipoprotein C-I; D001056:Apolipoproteins C / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D001057:Apolipoproteins E / Q000378:metabolism*; D001667:Binding, Competitive; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008079:Lipoproteins, VLDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D017433:Protein Structure, Secondary; D011817:Rabbits; D051381:Rats; D011971:Receptors, Immunologic / Q000378:metabolism*
D000596:Amino Acids; D053302:Apolipoprotein C-I; D001056:Apolipoproteins C; D001057:Apolipoproteins E; D008079:Lipoproteins, VLDL; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D010446:Peptide Fragments; D011971:Receptors, Immunologic