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Glycobiology Advance Access published online on April 2, 2003
Glycobiology, doi:10.1093/glycob/cwg067
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Submitted on January 6, 2003
Revised on March 4, 2003
Accepted on March 10, 2003

© 2003 Oxford University Press

ORIGINAL ARTICLES

Catalytic mechanism of the inverting N-acetylglucosaminyltransferase I: DFT quantum mechanical model of the reaction pathway and determination of the transition state structure

Igor Tvaroska 1, Isabelle André 2*, Jeremy P. Carver 2

1 GlycoDesign Inc., 480 University Avenue, Suite 900, Toronto, Ontario, Canada, M5G 1V2; Institute of Chemistry, Slovak Academy of Sciences, 845 38 Bratislava, Slovak Republic
2 GlycoDesign Inc., 480 University Avenue, Suite 900, Toronto, Ontario, Canada, M5G 1V2

* To whom correspondence should be addressed. E-mail: isabelle{at}glycodesign.com.

Abstract

The complex N-glycan structures on glycoproteins play important roles in cell adhesion and recognition events in metazoan organisms. A critical step in the biosynthetic pathway leading from high mannose to these complex structures includes the transfer of N-acetylglucosamine (GlcNAc) to a mannose residue by the inverting N-acetylglucosaminyltransferase I (GnT-I). The catalytic mechanism of this enzymatic reaction is explored herein using DFT quantum chemical methods. The computational model used to follow the reaction is based on the X-ray crystallographic structure of GnT-I and contains 127 atoms that represent fragments of residues critical for the substrate binding and catalysis. The mechanism of the catalytic reaction was monitored by means of a two-dimensional potential energy map calculated as a function of predefined reaction coordinates at the B3LYP/6-31G** level. This potential energy surface revealed one transition state associated with a reaction pathway following a concerted mechanism. The reaction barrier was estimated and the structure of the transition state was characterized at the B3LYP/6-311++G**// B3LYP/6-31G** level.


N-acetylglucosaminyltransferase I, catalytic mechanism, reaction pathway, transition state, quantum chemical calculations
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