Oxazoline or Oxazolinium Ion? The Protonation State and Conformation of the Reaction Intermediate of Chitinase Enzymes Revisited

Joan Coines, Mercedes Alfonso-Prieto, Xevi Biarnés, Antoni Planas, Carme Rovira

Research output: Indexed journal article Articlepeer-review

25 Citations (Scopus)

Abstract

The enzymatic hydrolysis of chitin, one of the most abundant carbohydrates in nature, is achieved by chitinases, enzymes of increasing importance in biomedicine and industry. Unlike most retaining glycosidases, family GH18 chitinases follow a substrate-assisted mechanism in which the 2-acetamido group of one N-acetylglucosamine monomer, rather than a basic residue of the enzyme, reacts with the sugar anomeric carbon, forming an intermediate that has been described as an oxazolinium ion. Based on QM/MM metadynamics simulations on chitinase B from Serratia marcescens, we show that the reaction intermediate of GH18 chitinases features instead a neutral oxazoline in a 4C1/4H5 conformation, with an oxazolinium ion being formed on the pathway towards the reaction products. The role of a well-defined hydrogen-bond network that operates around the N-acetyl group, orchestrating catalysis by protonation events, is discussed.

Original languageEnglish
Pages (from-to)19258-19265
Number of pages8
JournalChemistry - A European Journal
Volume24
Issue number72
DOIs
Publication statusPublished - 20 Dec 2018

Keywords

  • conformation analysis
  • glycosidases
  • molecular modeling
  • reaction intermediates
  • reaction mechanisms

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