A synthetic peptide mimic of plasma apolipoprotein E that binds the LDL receptor.
Human plasma apolipoprotein E (apoE) is a low density lipoprotein (LDL) receptor ligand. It targets cholesterol-rich lipoproteins to LDL receptors on both hepatic and peripheral cells. The region of apoE responsible for its binding to the LDL receptor has been localized to amino acids 140-160. An apoE 141-155 monomeric peptide and a dimeric 141-155 tandem peptide were synthesized and tested for their inhibition of 125I-LDL degradation by human fibroblasts and human monocytic-like cells, THP-1. The monomer had no activity at 250 microM, but the dimer inhibited 125I-LDL degradation by 50% at 5 microM. The inhibition was specific for the LDL receptor because the dimer did not inhibit the degradation of 125I-acetylated LDL by scavenger receptors expressed by phorbol ester-stimulated THP-1 cells. As reported for native apoE, amino acid substitutions of Lys-143----Ala, Leu-144----Pro, and Arg-150----Ala decreased the inhibitory effectiveness of the dimer. Furthermore, a trimer of the 141-155 sequence had a 20-fold greater inhibitory activity than the dimer. Studies with a radioiodinated dimer indicated that some of the inhibitory activity could be a result of the interaction of the dimer with LDL. However, direct binding of the 125I-dimeric peptide to THP-1 cells was observed as well. This binding was time-dependent, linear with increasing cell number, Ca(2+)- but not Mg(2+)-dependent, saturable, inhibited by lipoproteins, and increased by preculture of the cells in lipoprotein-depleted medium. Therefore, a synthetically prepared dimeric repeat of amino acid residues 141-155 of apoE binds the LDL receptor.
Dyer
C A
CA
Department of Immunology, Scripps Research Institute, La Jolla, California 92037.
Curtiss
L K
LK
D000595:Amino Acid Sequence; D001057:Apolipoproteins E / Q000138:chemical synthesis* / Q000378:metabolism; D001667:Binding, Competitive; D002460:Cell Line; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism; D010455:Peptides / Q000138:chemical synthesis; D011973:Receptors, LDL / Q000378:metabolism*
D001057:Apolipoproteins E; D010455:Peptides; D011973:Receptors, LDL