Glycobiology, 2001, Vol. 11, No. 1 37-45
© 2001 Oxford University Press
A new 
-1,2-N-acetylglucosaminyltransferase that may play a role in the biosynthesis of mammalian O-mannosyl glycans
Department of Glycobiology, Tokyo Metropolitan Institute of Gerontology, 35–2 Sakaecho, Itabashi-ku, Tokyo 173–0015, Japan, 2KIRIN Brewery Co., Ltd., Central Laboratories for Key Technology, 1–13–5 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa 236–0004, Japan, 3Research Department, The Noguchi Institute, 1–8–1 Kaga, Itabashi-ku, Tokyo 173–0003, Japan, and 4Department of Biochemistry, Institute of Medical Science, University of Tokyo, 4–6–1 Shirokanedai, Minato-ku, Tokyo 108–8639, Japan
Recent studies have shown that O-mannosyl glycans are present in several mammalian glycoproteins. Although knowledge on the functional roles of these glycans is accumulating, their biosynthetic pathways are poorly understood. Here we report the identification and initial characterization of a novel enzyme capable of forming GlcNAc
1-2Man linkage, namely UDP-N-acetylglucosamine: O-linked mannose -1,2-N-acetylglucosaminyltransferase in the microsome fraction of newborn rat brains. The enzyme transfers GlcNAc to -linked mannose residues, and the formed linkage was confirmed to be 1-2 on the basis of diplococcal -N-acetylhexosaminidase susceptibility and by high-pH anion-exchange chromatography. Its activity is linearly dependent on time, protein concentration, and substrate concentration and is enhanced in the presence of manganese ion. Its activity is not due to UDP-N-acetylglucosamine: 
-3-D-mannoside -1,2-N-acetylglucosaminyltransferase I (GnT-I) or UDP-N-acetylglucosamine: -6-D-mannoside -1,2-D-acetylglucosaminyltransferase II (GnT-II), which acts on the early steps of N-glycan biosynthesis, because GnT-I or GnT-II expressed in yeast cells did not show any GlcNAc transfer activity against a synthetic mannosyl peptide. Taken together, the results suggest that the GlcNAc transferase activity described here is relevant to the O-mannosyl glycan pathway in mammals.
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