Abstract
Seven imperfect repeats of a 40-amino acid cysteine-rich sequence constitute the ligand binding domain of the low density lipoprotein (LDL) receptor. To assess the contribution of each repeat, three site-directed mutations were made individually in each repeat: 1) deletion of the repeat, 2) substitution of a conserved isoleucine with aspartic acid, and 3) substitution of a conserved aspartic acid with tyrosine. cDNAs containing these mutations were transfected into simian COS cells and assayed for their ability to bind LDL, which contains a 500-kDa protein ligand (apoB-100), and β-migrating very low density lipoprotein (β-VLDL), which contains multiple copies of a 33-kDa ligand (apoE). The results showed that binding of the two ligands required different combinations of repeats. LDL binding required repeats 3-7; deletion of any one of these repeats markedly reduced LDL binding. In contrast, β-migrating very low density lipoprotein binding was insensitive to the loss of any single repeat with the important exception of repeat 5, whose loss reduced binding by 60%. The same effects were obtained when each of the repeats was altered by either of the two substitution mutations. The current findings suggest that a multiplicity of cysteine-rich repeats may allow a single protein to bind several different protein ligands by employing different combinations of repeats.
Original language | English (US) |
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Pages (from-to) | 21682-21688 |
Number of pages | 7 |
Journal | Journal of Biological Chemistry |
Volume | 264 |
Issue number | 36 |
State | Published - 1989 |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology