Domain Swapping Reveals That Low Density Lipoprotein (LDL) Type A Repeat Order Affects Ligand Binding to the LDL Receptor

• Published in: The Journal of biological chemistry 2009-05, Vol.284 (20), p.13396-13400
• Main Authors: Yamamoto, Taichi, Ryan, Robert O.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence - genetics; Cell Line; Humans; Ligands; Lipids and Lipoproteins: Metabolism, Regulation, and Signaling; Lipoproteins, LDL - genetics; Lipoproteins, LDL - metabolism; Protein Binding - physiology; Protein Structure, Tertiary - physiology; Receptors, LDL - genetics; Receptors, LDL - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M900194200

The low density lipoprotein receptor (LDLR) plays a key role in plasma cholesterol homeostasis by binding and internalizing lipoprotein ligands. Studies have revealed that one or more of the seven LDL type A repeats (LA1–LA7) in the receptor are responsible for apolipoprotein binding. In the present study, protein engineering was performed to swap or replace key LA repeats in a recombinant soluble LDLR (sLDLR). Although wild type sLDLR showed strong ligand binding activity, an sLDLR variant in which LA repeat 5 was replaced by a second copy of LA repeat 2 showed low binding activity. Likewise, a variant wherein LA repeats 2 and 5 were swapped displayed low binding activity. At the same time, substitution of LA repeat 2 with a second a copy of repeat 5 resulted in a receptor with ligand binding activity similar to wild type LDLR. When binding assays were conducted with human low density lipoprotein as ligand, LA repeat order was a less important determinant of binding activity. Taken together, the data indicate that the sequential order of LA repeats plays a key role in ligand binding properties of LDLR.