O-Mannosylation in Mammalian Cells

The O -mannosyl glycan is present in a limited number of glycoproteins of brain, nerve, and skeletal muscle. α-Dystroglycan is one of the O -mannosylated proteins and is a central component of the dystrophin-glycoprotein complex that has been shown to be related to the onset of muscular dystrophy. We have identified and characterized glycosyltransferases, protein O -mannose β1,2-N -acetylglucosaminyltransferase (POMGnT1) and protein O -mannosyltransferase 1 (POMT1), involved in the biosynthesis of O -mannosyl glycans. We subsequently found that loss of function of the POMGnT1 gene is responsible for muscle-eye-brain disease (MEB). It has also been reported that the POMT1 gene is responsible for Walker-Warburg syndrome (WWS). MEB and WWS are autosomal recessive disorders characterized by congenital muscular dystrophies with neuronal migration disorders. Therefore, the ability to assay enzyme activities of mammalian O -mannosylation would facilitate progress in the identification of other O -mannosylated proteins, the elucidation of their functional roles, and the understanding of muscular dystrophies. This protocol describes assay methods for the mammalian POMT and POMGnT.