Protein O-mannosyltransferases transfer a mannose residue from dolichyl phosphate D-mannose to the oxygen atom of the hydroxyl group of selected serine/threonine residues. In contrast to yeast, O-Man glycosylation in metazoans is found only on select proteins. The evolutionary conserved POMT1/POMT2 enzymes target the dystroglycan protein, while the TMTC proteins selectively serve cadherins and protocadherins. (Adapted from PMID:28973932 and FBrf0244700.)
These enzymes are localized in the endoplasmic reticulum.