Reaction mechanisms of thiamin diphosphate enzymes: New insights into the role of a conserved glutamate residue

Boaz Shaanan, David M. Chipman

Research output: Contribution to journalShort surveypeer-review

26 Scopus citations

Abstract

Subsequent to the demonstration in the late 1950s of the catalytic power of the C2 anion-ylid of thiamin diphosphate, further convincing evidence was provided demonstrating that the 4′-aminopyrimidine group plays a vital role in activation of this cofactor. Structural evidence from several crystal structures of thiamin diphosphate-dependent enzymes emphasized the presence of a glutamate residue in hydrogen-bonding distance from N1′ as a conserved element in these enzymes. The important role of this conserved glutamate in promoting C2-H ionization and activation of thiamin diphosphate was emphasized by site-directed mutagenesis studies. This role was further elaborated by spectroscopic studies of the 4′-aminopyrimidine-iminopyrimidine tautomerization. The low polarity of the environment of the protein-bound thiazolium is an additional factor in the stabilization of the C2 anion-ylid. The recently determined crystal structure and mutagenesis studies of glyoxylate carboligase, in which the position of the conserved glutamate is occupied by valine, now show that, for the multi-step reaction catalyzed by this enzyme, the advantages of accelerating the ionization of C2-H by re-introducing a carboxylate are outweighed by the apparent overstabilization of intermediates.

Original languageEnglish
Pages (from-to)2447-2453
Number of pages7
JournalFEBS Journal
Volume276
Issue number9
DOIs
StatePublished - 1 May 2009

Keywords

  • 3D structure
  • Aminopyrimidine-iminopyrimidine tautomerization
  • Carboligation
  • Conserved glutamate
  • Effective dielectric constant
  • Glyoxylate carboligase
  • Thiamin
  • Thiamin diphosphate-dependent enzyme

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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