Mannosyltransferase involved in glycosylphosphatidylinositol-anchor biosynthesis. Transfers the third alpha-1,2-mannose to Man2-GlcN-acyl-PI during GPI precursor assembly. Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. The protozoan parasite evades the immune response of mammalian hosts and digestion in the gut of the insect vector by means of its coat proteins tethered to the cell surface via GPI-anchors. GPI10 is essential for growth of mammalian stage bloodstream form, while procyclic form (insect stage parasites) are viable but grow slower, suggesting that inhibition of GPI synthesis may be an effective chemotherapy against African trypanosomiasis. Belongs to the glycosyltransferase 22 family. PIGB subfamily.