Lectin-like, oxidized low-density lipoprotein (LDL) receptor 1, LOX-1, is the major receptor for oxidized LDL (OxLDL) in endothelial cells. We have determined the crystal structure of the ligand binding domain of LOX-1, with a short stalk region connecting the domain to the membrane-spanning region, as a homodimer linked by an interchain disulfide bond. In vivo assays with LOX-1 mutants revealed that the "basic spine," consisting of linearly aligned arginine residues spanning over the dimer surface, is responsible for ligand binding. Single amino acid substitution in the dimer interface caused a severe reduction in LOX-1 binding activity, suggesting that the correct dimer arrangement is crucial for binding to OxLDL. Based on the LDL model structure, possible binding modes of LOX-1 to OxLDL are proposed.
LOX-1 (lectin-like oxidized low-density lipoprotein receptor 1) is the major oxidized LDL (OxLDL) receptor on endothelial cells. The extracellular part of LOX-1 comprises an 82-residue stalk region (NECK) and a C-type lectin-like ligand-binding domain (CTLD). The NECK displays sequence similarity to the coiled-coil region of myosin, having been suggested it adopts a rod-like structure. In this article, we report the structural analyses of human LOX-1 NECK using a variety of approaches including limited proteolysis, chemical cross-linking, circular dichroism (CD) and NMR. Our analysis reveals a unique structural feature of the LOX-1 NECK. Despite significant sequence similarity with the myosin coiled-coil, LOX-1 NECK does not form a uniform rod-like structure. Although not random, one-third of the N-terminal NECK is less structured than the remainder of the protein and is highly sensitive to cleavage by a variety of proteases. The coiled-coil structure is localized at the C-terminal part of the NECK, but is in dynamic equilibrium among multiple conformational states on a mus-ms time scale. This chimeric structural property of the NECK region may enable clustered LOX-1 on the cell surface to recognize OxLDL.
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