InterPro domain: IPR039521

Many eukaryotic cell surface proteins are bound to the membrane via the glycosylphosphatidylinositol (GPI) anchor. The GPI anchor precursor is synthesized in the endoplasmic reticulum (ER) by sequential enzymatic reactions. Phosphatidyl-inositol glycan B (PIG-B) is a GPI mannosyltransferase 3, a member of the alpha2-mannosyltransferase family [ 1 , 2 ]. PIG-B transfers the third alpha-1,2-mannose to Man2-GlcN-acyl-PI during GPI precursor assembly [ 3 ]. Gpi10 is the functional homologue in yeast [ 4 ]. In Arabidopsis thaliana, APTG1 encodes a putative GPI mannosyltransferase 3 homologue which has been shown to be involved in both vegetative and reproductive development, likely through processing and proper targeting of GPI-anchored proteins [ 5 ].

1. ALG9 mannosyltransferase is involved in two different steps of lipid-linked oligosaccharide biosynthesis. Glycobiology 15, 1156-63
2. Common origin and evolution of glycosyltransferases using Dol-P-monosaccharides as donor substrate. Mol. Biol. Evol. 19, 1451-63
3. PIG-B, a membrane protein of the endoplasmic reticulum with a large lumenal domain, is involved in transferring the third mannose of the GPI anchor. EMBO J. 15, 4254-61
4. Saccharomyces cerevisiae GPI10, the functional homologue of human PIG-B, is required for glycosylphosphatidylinositol-anchor synthesis. Biochem. J. 332 ( Pt 1), 153-9
5. ABNORMAL POLLEN TUBE GUIDANCE1, an Endoplasmic Reticulum-Localized Mannosyltransferase Homolog of GLYCOSYLPHOSPHATIDYLINOSITOL10 in Yeast and PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS B in Human, Is Required for Arabidopsis Pollen Tube Micropylar Guidance and Embryo Development. Plant Physiol. 165, 1544-1556