A Full QM Computational Study of the Catalytic Mechanism of α‐1, 4‐Glucan Lyases. Issue 12 (17th April 2018)

• Record Type: Journal Article
• Authors: Campesato, Lara; Marforio, Tainah Dorina; Giacinto, Pietro; Calvaresi, Matteo; Bottoni, Andrea
• Is Part Of: Chemphyschem. Volume 19:Issue 12(2018)
• Page Start: 1514
• Page End: 1521
• Publication Date: 2018-04-17
• Subjects: DFT calculations -- glycoside hydrolases -- glycosylation -- reaction mechanism -- tautomerization; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201701332
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: We investigated the catalytic mechanism of α‐1, 4‐glucan lyases using a full QM DFT approach based on the M06‐2X functional. The reaction profile of the whole catalytic process can be divided into three phases: glycosylation, deglycosylation‐elimination and tautomerization. Glycosylation is a highly asynchronous SN 1‐like process with an energy barrier of 10.2 kcal mol −1 . A proton moves from the Asp 665 residue to the glycosidic oxygen. Asp 553 acts as a nucleophile and attacks the anomeric carbon causing the cleavage of the glycosidic bond. Deglycosilation‐elimination is the rate‐determining step of the entire process with an overall barrier of 18.3 kcal mol −1 . The final step (restoring the catalyst and tautomerization) occurs rather easily, since the Asp 553 carboxylate group "assists" the proton transfer in the tautomerization process. Our computations clearly indicate that tautomerization must occur inside the enzyme before leaving the active site rather than in the aqueous solution. Outside of the protein environment the enol‐AF→keto‐AF process "assisted" by a water molecule has a barrier of 35.8 kcal mol −1 . Abstract : The catalytic mechanism of α‐1, 4‐glucan lyase is investigated using a full QM DFT approach. The reaction profile of the whole catalytic process consists of three steps: glycosylation, deglycosylation‐elimination (the rate‐determining step) and tautomerization. The computations clearly indicate that tautomerization must occur inside the enzyme.