Part of the complex catalyzing the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol, the first step of GPI biosynthesis.
Catalysis of a biochemical reaction at physiological temperatures. In biologically catalyzed reactions, the reactants are known as substrates, and the catalysts are naturally occurring macromolecular substances known as enzymes. Enzymes possess specific binding sites for substrates, and are usually composed wholly or largely of protein, but RNA that has catalytic activity (ribozyme) is often also regarded as enzymatic.
Glycosylphosphatidylinositol (GPI) protein anchors are ubiquitous in eukaryotic cells. GPI anchors are synthesized in the endoplasmic reticulum by actions of ten or more gene products. The first step of the biosynthesis, the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol, is mediated by at least three genes in mammalian cells (PIG-A, PIG-H and PIG-C) and in yeast (GPI1, GPI2 and GPI3/SPT14/CWH6). PIG-A is homologous to GPI3/SPTI4/CWH6. However, PIG-H has no homology with GPI1 or GPI2. Here we cloned a human homologue of GPI2 and showed that it is PIG-C. PIG-C protein is a 297 amino-acid membrane protein in the endoplasmic reticulum that has 20% amino acid identity with GPI2. Since there are several human EST sequences that have homology to GPI1, our results suggest that four genes are involved in the first step of GPI anchor synthesis in mammalian cells.
The chemical reactions and pathways resulting in the formation of a glycosylphosphatidylinositol (GPI) anchor that attaches some membrane proteins to the lipid bilayer of the cell membrane. The phosphatidylinositol group is linked via the C-6 hydroxyl residue of inositol to a carbohydrate chain which is itself linked to the protein via an ethanolamine phosphate group, its amino group forming an amide linkage with the C-terminal carboxyl of the protein. Some GPI anchors have variants on this canonical linkage.
Glycosylphosphatidylinositol (GPI) protein anchors are ubiquitous in eukaryotic cells. GPI anchors are synthesized in the endoplasmic reticulum by actions of ten or more gene products. The first step of the biosynthesis, the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol, is mediated by at least three genes in mammalian cells (PIG-A, PIG-H and PIG-C) and in yeast (GPI1, GPI2 and GPI3/SPT14/CWH6). PIG-A is homologous to GPI3/SPTI4/CWH6. However, PIG-H has no homology with GPI1 or GPI2. Here we cloned a human homologue of GPI2 and showed that it is PIG-C. PIG-C protein is a 297 amino-acid membrane protein in the endoplasmic reticulum that has 20% amino acid identity with GPI2. Since there are several human EST sequences that have homology to GPI1, our results suggest that four genes are involved in the first step of GPI anchor synthesis in mammalian cells.
Protein involved in the synthesis or the attachment to a protein of a GPI-anchor (glycosylphosphatidylinositol anchor) or a GPI-like-anchor (glycosylsphingolipidinositol anchor), both of which have complex oligoglycan linked to a phospholipidinositol molecule that serves to attach the C-terminus of some extracellular membrane proteins to the lipid bilayer of a membrane. The core glycolipid is composed of a tetraglycan: three mannose units and one glucosamine linked to a phospholipidinositol. The terminal mannose is linked to the protein via an ethanolamine attached to the C-terminal of the mature protein. The core structure is conserved from protozoa to humans. There are, however, marked differences in the glycosyl side chains attached to the core glycolipid. The phospholipid component may be either a phosphatide (two long chain fatty acids attached by ester linkage to glycerol phosphate) or a sphingolipid (a long chain fatty acid attached by amide linkage to a ceramide phosphate). Some yeast and Dictyosteliida synthesize the GPI-like anchor de novo, whereas other organisms may interconvert the lipid components by a "resculpting" process after the anchor is attached to the protein.
Enzymes that catalyze the transfer of glycosyl (sugar) residues to an acceptor, both during degradation (cosubstrates= water or inorganic phosphate) and during biosynthesis of polysaccharides, glycoproteins and glycolipids. In biosynthetic glycosyl transfers, the common activated monomeric sugar intermediate is a nucleoside diphosphate sugar.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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