• Pamela Stanley


Structural analyses of sugars on secreted glycoproteins performed about 30 years ago revealed bi-, tri-, and tetraantennary N-glycans in which GlcNAc residues linked to a conserved trimannosyl core initiated each antenna. These same structures were lectin binding sites on red cell glycoproteins (Kornfeld and Kornfeld 1970), prompting the search for the GlcNAc-transferases that catalyzed the addition of each GlcNAc residue. N-Acetylglucosaminyltransferase-I (GnT-I) was the first N-glycan branching GlcNAc- transferase for which an assay was developed (Gottlieb et al. 1975; Stanley et al. 1975). It is a Type II transmembrane protein of ~447 amino acids (Kumar et al. 1990; Sarkar et al. 1991) that resides in the medial/trans Golgi. GnT-I catalyzes the transfer of GlcNAc from UDP-GlcNAc to the terminal α-1,3-linked Man in Man5GlcNAc2Asn to initiate the synthesis of hybrid and complex N-linked glycans in multicellular organisms (reviewed in Kornfeld and Kornfeld 1985). It is not found in yeast or bacteria. The human gene encoding GnT-I is termed MGAT1 and resides on chromosome 5q35 (Kumar et al. 1992; Tan et al. 1995), and the mouse gene, Mgat1, is on chromosome 11 (Pownall et al. 1992). Two transcripts of ~2.9kb and ~3.3 kb are observed in most mammalian tissues, with the shorter transcript predominating in liver, and the longer transcript in brain (Yang et al. 1994; Yip et al. 1997; Fukada et al. 1998). In mammals, the coding region is in a single exon and the Mgatl gene is ubiquitously expressed. Mutant mice with a targeted Mgatl gene mutation that inactivates GnT-I die at mid-gestation (Ioffe and Stanley 1994; Metzler et al. 1994). However, cultured cells (Gottlieb et al. 1975; Meager et al. 1975; Stanley et al. 1975) and plants (von Schaewen et al. 1993) lacking GnT-I are viable and healthy.


Chinese Hamster Ovary Cell GlcNAc Residue Lectin Binding Site Chinese Hamster Ovary Cell Mutant Glycosylation Mutant 
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© Springer Japan 2002

Authors and Affiliations

  • Pamela Stanley
    • 1
  1. 1.Department of Cell BiologyAlbert Einstein College of MedicineBronxUSA

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