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].
Maeda Y, Watanabe R, Harris CL, Hong Y, Ohishi K, Kinoshita K, Kinoshita T.
PIG-M transfers the first mannose to glycosylphosphatidylinositol on the lumenal side of the ER.
EMBO J. 20 250-61 2001
[PubMed: 11226175] http://dx.doi.org/10.1093/emboj/20.1.250
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