PIG-M has a DXD motif. The DXD motif is found in many glycosyltransferases that utilise nucleotide sugars. It is thought that the motif is involved in the binding of a manganese ion that is required for association of the enzymes with nucleotide sugar substrates [1].

1: PIG-M transfers the first mannose to glycosylphosphatidylinositol on the lumenal side of the ER. Maeda Y, Watanabe R, Harris CL, Hong Y, Ohishi K, Kinoshita K, Kinoshita T; EMBO J 2001;20:250-261. PMID:11226175