Molecular basis of N-acetylglucosaminyltransferase I deficiency in Arabidopsis thaliana plants lacking complex N-glycans

Biochem J. 2005 Apr 15;387(Pt 2):385-91. doi: 10.1042/BJ20041686.


GnTI (N-acetylglucosaminyltransferase I) is a Golgi-resident enzyme essential for the processing of high-mannose to hybrid and complex N-glycans. The Arabidopsis thaliana cgl mutant lacks GnTI activity and as a consequence accumulates oligomannosidic structures. Molecular cloning of cgl GnTI cDNA revealed a point mutation, which causes a critical amino acid substitution (Asp144-->Asn), thereby creating an additional N-glycosylation site. Heterologous expression of cgl GnTI in insect cells confirmed its lack of activity and the use of the N-glycosylation site. Remarkably, introduction of the Asp144-->Asn mutation into rabbit GnTI, which does not result in the formation of a new N-glycosylation site, led to a protein with strongly reduced, but still detectable enzymic activity. Expression of Asn144 rabbit GnTI in cgl plants could partially restore complex N-glycan formation. These results indicate that the complete deficiency of GnTI activity in cgl plants is mainly due to the additional N-glycan, which appears to interfere with the proper folding of the enzyme.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Arabidopsis / enzymology*
  • Arabidopsis / genetics*
  • Cell Line
  • Molecular Sequence Data
  • Mutation
  • N-Acetylglucosaminyltransferases / genetics
  • N-Acetylglucosaminyltransferases / metabolism*
  • Plant Leaves / metabolism
  • Plants, Genetically Modified
  • Polysaccharides / metabolism*
  • Rabbits
  • Sequence Alignment
  • Sequence Homology, Amino Acid


  • Polysaccharides
  • N-Acetylglucosaminyltransferases
  • alpha-1,3-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase I