Meta-Biol

• Pathways

Dolichyl-phosphate mannosyltransferase (DPM), a heterotrimeric protein embedded in the endoplasmic reticulum membrane, mediates the transfer of mannose (from cytosolic GDP-mannose) to dolichyl phosphate (DOLP) to form dolichyl-phosphate-mannose (DOLPman). The first subunit of the heterotrimer (DPM1) appears to be the actual catalyst, and the other two subunits (DPM2 and 3) appear to stabilise it (Maeda et al. 2000). DPM2 is essential for the ER localisation and stable expression of DPM1 and it enhances binding of the substrate dolichyl phosphate (Maeda et al. 1998). Defects in DPM2 can cause congenital disorder of glycosylation 1u (DPM2-CDG, CDG1u; MIM:615042), a multisystem disorder caused by a defect in glycoprotein biosynthesis and characterised by under-glycosylated serum glycoproteins (Barone et al. 2012). CDG type 1 diseases result in a wide variety of clinical features, such as defects in the nervous system development, psychomotor retardation, dysmorphic features, hypotonia, coagulation disorders, and immunodeficiency. One mutation, a tyr23-cys (Y23C) substitution at a highly conserved residue encoding a transmembrane domain, can result in the clinical features of DPM2-CDG (Barone et al. 2012).