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Probing synergy between two catalytic strategies in the glycoside hydrolase O-GlcNAcase using multiple linear free energy relationships

Academic Article
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Overview

authors

  • Greig, I. R.
  • Macauley, Matthew
  • Williams, I. H.
  • Vocadlo, D. J.

publication date

  • September 2009

journal

  • Journal of the American Chemical Society  Journal

abstract

  • Human O-GlcNAcase plays an important role in regulating the post-translational modification of serine and threonine residues with beta-O-linked N-acetylglucosamine monosaccharide unit (O-GlcNAc). The mechanism of O-GlcNAcase involves nucleophilic participation of the 2-acetamido group of the substrate to displace a glycosidically linked leaving group. The tolerance of this enzyme for variation in substrate structure has enabled us to characterize O-GlcNAcase transition states using several series of substrates to generate multiple simultaneous free-energy relationships. Patterns revealing changes in mechanism, transition state, and rate-determining step upon concomitant variation of both nucleophilic strength and leaving group abilities are observed. The observed changes in mechanism reflect the roles played by the enzymic general acid and the catalytic nucleophile. Significantly, these results illustrate how the enzyme synergistically harnesses both modes of catalysis; a feature that eludes many small molecule models of catalysis. These studies also suggest the kinetic significance of an oxocarbenium ion intermediate in the O-GlcNAcase-catalyzed hydrolysis of glucosaminides, probing the limits of what may be learned using nonatomistic investigations of enzymic transition-state structure and offering general insights into how the superfamily of retaining glycoside hydrolases act as efficient catalysts.

subject areas

  • Acetylglucosamine
  • Biocatalysis
  • Glycosides
  • Humans
  • Hydrolysis
  • Isotopes
  • Kinetics
  • Linear Models
  • Solvents
  • Stereoisomerism
  • Substrate Specificity
  • Thermodynamics
  • beta-N-Acetylhexosaminidases
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Identity

International Standard Serial Number (ISSN)

  • 0002-7863

Digital Object Identifier (DOI)

  • 10.1021/ja904506u

PubMed ID

  • 19715310
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Additional Document Info

start page

  • 13415

end page

  • 13422

volume

  • 131

issue

  • 37

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