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Abstract

Lectin-like oxidized LDL (ox-LDL) receptor-1 (LOX-1) is a type-II transmembrane protein that belongs to the C-type lectin family of molecules. LOX-1 acts as a cell surface endocytosis receptor and mediates the recognition and internalization of ox-LDL by vascular endothelial cells. Internalization of ox-LDL by LOX-1 results in a number of pro-atherogenic cellular responses implicated in the development and progression of atherosclerosis. In an effort to elucidate the functional domains responsible for the binding of ox-LDL to the receptor, a series of site-directed mutants were designed using computer modeling and X-ray crystallography to study the functional role of the hydrophobic tunnel present in the LOX-1 receptor. The isoleucine residue (I(149)) sitting at the gate of the channel was replaced by phenylalanine, tyrosine, or glutamic acid to occlude the channel opening and restrict the docking of ligands to test its functional role in the binding of ox-LDL. The synthesis, intracellular processing, and cellular distribution of all mutants were identical to those of wild type, whereas there was a marked decrease in the ability of the mutants to bind ox-LDL. These studies suggest that the central hydrophobic tunnel that extends through the entire LOX-1 molecule is a key functional domain of the receptor and is critical for the recognition of modified LDL.