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Francone OL, Tu M, Royer LJ, Zhu J, Stevens K, Oleynek JJ, Lin Z, Shelley L, Sand T, Luo Y, Kane CD. The hydrophobic tunnel present in LOX-1 is essential for oxidized LDL recognition and binding. J Lipid Res 2008; 50:546-555. [PMID: 18845619 DOI: 10.1194/jlr.m800474-jlr200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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.
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Affiliation(s)
- Omar L Francone
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340.
| | - Meihua Tu
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Lori J Royer
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Jian Zhu
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Kimberly Stevens
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Joseph J Oleynek
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Zhiwu Lin
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Lorraine Shelley
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Thomas Sand
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Yi Luo
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
| | - Christopher D Kane
- Department of Atherosclerosis Biology, Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340
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Park H, Adsit FG, Boyington JC. The 1.4 angstrom crystal structure of the human oxidized low density lipoprotein receptor lox-1. J Biol Chem 2005; 280:13593-9. [PMID: 15695803 DOI: 10.1074/jbc.m500768200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The lectin-like oxidized low density lipoprotein receptor-1 (Lox-1) mediates the recognition and internalization of oxidatively modified low density lipoprotein by vascular endothelial cells. This interaction results in a number of pro-atherogenic cellular responses that probably play a significant role in the pathology of atherosclerosis. The 1.4 angstrom crystal structure of the extracellular C-type lectin-like domain of human Lox-1 reveals a heart-shaped homodimer with a ridge of six basic amino acids extending diagonally across the apolar top of Lox-1, a central hydrophobic tunnel that extends through the entire molecule, and an electrostatically neutral patch of 12 charged residues that resides next to the tunnel at each opening. Based on the arrangement of critical binding residues on the Lox-1 structure, we propose a binding mode for the recognition of modified low density lipoprotein and other Lox-1 ligands.
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Affiliation(s)
- HaJeung Park
- Biomolecular Crystallography Group, Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
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Xie Q, Matsunaga S, Niimi S, Ogawa S, Tokuyasu K, Sakakibara Y, Machida S. Human lectin-like oxidized low-density lipoprotein receptor-1 functions as a dimer in living cells. DNA Cell Biol 2004; 23:111-7. [PMID: 15000751 DOI: 10.1089/104454904322759920] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a unique scavenger receptor that plays important roles in atherogenesis and has been thought to function as a monomer. Using coimmunoprecipitation studies, we demonstrate that human LOX-1 (hLOX-1) forms constitutive homo-interactions in vivo. Western blot analysis of cell lysates under nonreducing or reducing conditions revealed one clear immunoreactive species corresponding to the size of a putative receptor dimer or a monomer, respectively, consistent with the presence of disulfide-linked hLOX-1 complexes. Site-directed mutagenesis studies indicated that cysteine 140 has a key role in the formation of these disulfide-linked hLOX-1 dimers. Eliminating this intermolecular disulfide bond markedly impairs the recognition of Escherichia coli by hLOX-1. Furthermore, these dimers can act as a "structural unit" to form noncovalently associated oligomers, as demonstrated by a membrane-impermeant crosslinker, which resulted in immunoreactive species corresponding to the sizes of putative tetramers and hexamers. These results provide the first evidence for the existence of hLOX-1 dimers/oligomers.
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Affiliation(s)
- Qiuhong Xie
- National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan
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Xie Q, Matsunaga S, Shi X, Ogawa S, Niimi S, Wen Z, Tokuyasu K, Machida S. Refolding and characterization of the functional ligand-binding domain of human lectin-like oxidized LDL receptor. Protein Expr Purif 2003; 32:68-74. [PMID: 14680941 DOI: 10.1016/s1046-5928(03)00220-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2003] [Revised: 07/08/2003] [Indexed: 11/29/2022]
Abstract
Lectin-like oxidized low-density lipoprotein receptor (LOX-1), a type II membrane protein that can recognize a variety of structurally unrelated macromolecules, plays an important role in host defense and is implicated in atherogenesis. To understand the interaction between human LOX-1 and its ligands, in this study the functional C-type lectin-like domain (CTLD) of LOX-1 was reconstituted at high efficiency from inactive aggregates in Escherichia coli using a refolding technique based on an artificial chaperone. The CD spectra of the purified domain suggested that the domain has alpha-helical structure and the blue shift of Trp residues was observed on refolding of the domain. Like wild-type hLOX-1, the refolded CTLD domain was able to bind modified LDL. Thus, even though CTLD contains six Cys residues that form disulfide bonds, it recovered its specific binding ability on refolding. This suggests that the correct disulfide bonds in CTLD were formed by the artificial chaperone technique. Although the domain lacked N-glycosylation, it showed high affinity for its ligand in surface plasmon resonance experiments. Thus, unglycosylated CTLD is sufficient for binding modified LDL.
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Affiliation(s)
- Qiuhong Xie
- National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan
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