Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

By expression cloning using fluorescent-labeled high density lipoprotein (HDL), we isolated two clones that conferred the cell surface binding of HDL. Nucleotide sequence of the two clones revealed that one corresponds to scavenger receptor class B, type 1 (SRBI) and the other encoded a novel protein with 228 amino acids. The primary structure of the newly identified HDL-binding protein resembles GPI-anchored proteins consisting of an N-terminal signal sequence, an acidic region with a cluster of aspartate and glutamate residues, an Ly-6 motif highly conserved among the lymphocyte antigen family, and a C-terminal hydrophobic region. This newly identified HDL-binding protein designated GPI-anchored HDL-binding protein 1 (GPI-HBP1), was susceptible to phosphatidylinositol-specific phospholipase C treatment and binds HDL with high affinity (calculated K(d) = 2-3 microg/ml). Similar to SRBI, GPI-HBP1 mediates selective lipid uptake but not the protein component of HDL. Among various ligands for SRBI, HDL was most preferentially bound to GPI-HBP1. In contrast to SRBI, GPI-HBP1 lacked HDL-dependent cholesterol efflux. The GPI-HBP1 transcripts were detected with the highest levels in heart and, to a much lesser extent, in lung and liver. In situ hybridization revealed the accumulation of GPI-HBP1 transcripts in cardiac muscle cells, hepatic Kupffer cells and sinusoidal endothelium, and bronchial epithelium and alveolar macrophages in the lung.
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PMID:Expression cloning and characterization of a novel glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein, GPI-HBP1. 1249 72

GPIHBP1, a glycosylphosphatidylinositol-anchored endothelial cell protein of the lymphocyte antigen 6 (Ly6) family, binds lipoprotein lipase (LPL) avidly and is required for the lipolytic processing of triglyceride-rich lipoproteins. GPIHBP1 contains two key structural motifs, an acidic domain and an Ly6 motif (a three-fingered domain specified by 10 cysteines). The acidic domain is required for LPL binding, but the importance of the Ly6 domain is less clear. To explore that issue, we transfected cells with a wild-type GPIHBP1 expression vector or mutant GPIHBP1 vectors in which specific cysteines in the Ly6 domain were changed to alanine. The mutant GPIHBP1 proteins reached the cell surface, as judged by antibody binding studies and by the ability of a phosphatidylinositol-specific phospholipase C to release these proteins from the cell surface. However, cells expressing the cysteine mutants could not bind LPL. The acidic domain of the cysteine mutants appeared to remain accessible, as judged by binding studies with an antibody against the acidic domain. We also developed a cell-free assay of LPL binding. We created a rat monoclonal antibody against the carboxyl terminus of mouse GPIHBP1 and used that antibody to coat agarose beads. We then tested the ability of soluble forms of GPIHBP1 that had been immobilized on monoclonal antibody-coated beads to bind LPL. In this assay, wild-type soluble GPIHBP1 bound LPL avidly, but the cysteine mutants did not. Thus, our studies suggest that a structurally intact Ly6 domain (in addition to the acidic domain) is essential for LPL binding.
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PMID:Highly conserved cysteines within the Ly6 domain of GPIHBP1 are crucial for the binding of lipoprotein lipase. 1972 83