Oxazoline or Oxazolinium Ion? The Protonation State and Conformation of the Reaction Intermediate of Chitinase Enzymes Revisited. Issue 72 (29th November 2018)

• Record Type: Journal Article
• Authors: Coines, Joan; Alfonso‐Prieto, Mercedes; Biarnés, Xevi; Planas, Antoni; Rovira, Carme
• Is Part Of: Chemistry. Volume 24:Issue 72(2018)
• Page Start: 19258
• Page End: 19265
• Publication Date: 2018-11-29
• Subjects: conformation analysis -- glycosidases -- molecular modeling -- reaction intermediates -- reaction mechanisms; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201803905
• Languages: English
• ISSNs: 0947-6539

Abstract

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 4 C 1 / 4 H 5 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. Abstract : Probing reaction intermediates : QM/MM metadynamics simulations have been used to uncover the oxazoline nature of the reaction intermediate of GH18 chitinases, its chair‐like conformation, and the proton‐transfer cascade taking place during catalysis.