Auxiliary active site mutations enhance the glycosynthase activity of a GH18 chitinase for polymerization of chitooligosaccharides

Cristina Alsina, Enea Sancho-Vaello, Almudena Aranda-Martínez, Magda Faijes, Antoni Planas

Research output: Indexed journal article Articlepeer-review

12 Citations (Scopus)

Abstract

Depolymerization of chitin results in chitooligosaccharides (COS) that induce immunostimulatory effects and disease protective responses and have many potential applications in agriculture and medicine. Isolation of bioactive COS with degree of polymerization (DP) larger than six from chitin hydrolyzates is hampered by their water insolubility. Enzymatic synthesis by exploiting the transglycosylation activity of GH18 chitinases offers a potential strategy to access oligomers in the range of bioactive DPs. We engineered SpChiD chitinase as a glycosynthase by mutation of the assisting residue of the catalytic triad in the substrate-assisted mechanism for polymerization of an oxazoline substrate (DP5ox). The insoluble polymer containing DP10 was partially hydrolyzed due to the significant residual hydrolase activity of the mutant enzyme. Combined mutations that strongly reduce the hydrolytic activity, in which the original catalytic triad only retains the essential acid/base residue, together with neighboring mutations in the -1/+1 subsites region, render glycosynthase-like chitinases able to produce chitin oligomers with DP10 as major product in good yields.

Original languageEnglish
Article number117121
JournalCarbohydrate Polymers
Volume252
DOIs
Publication statusPublished - 15 Jan 2021

Keywords

  • Chitin
  • Chitinase
  • Chito-oligosaccharides
  • Glycosynthase
  • Oxazoline donor
  • Polymerization
  • Substrate-assisted catalysis
  • Synthetic chitin polymers

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