A Recombinant Fungal Chitin Deacetylase Produces Fully Defined Chitosan Oligomers with Novel Patterns of Acetylation

We have recently shown that these two chitin deacetylases can be combined to yield the dideacetylated partially acetylated chitosan oligosaccharides GlcN2-glycosidically linked N-acetylglucosamine (nϪ2)

Shoa Naqvi

2016

Scholarcy highlights

  • Acetylated chitosan oligosaccharides are potent biologics with many potential applications, and their bioactivities are believed to be dependent on their structure, i.e., their degrees of polymerization and acetylation, as well as their pattern of acetylation
  • We successfully achieved heterologous expression of a fungal chitin deacetylase gene from the basidiomycete Puccinia graminis f. sp. tritici in the periplasm of E. coli as a fusion protein with the maltose-binding protein; this strategy allows the production of these difficult-to-express enzymes in sufficient quantities for them to be characterized and optimized through protein engineering
  • Detailed structure-function relationships are not yet fully understood, in particular regarding the postulated role of the pattern of acetylation. This is mostly because all chitosans available commercially today are prepared from chitin by partial de-N-acetylation, or by full de-N-acetylation followed by partial re-N-acetylation, and the chemical methods used for these conversions invariably lead to chitosans with random patterns of acetylation
  • Most of the bacterial and fungal chitin deacetylases analyzed to date yield mixtures of partially acetylated chitosan oligosaccharides and often eventually fully de-N-acetylate chitin oligomers, even if the sequence of deacetylation varies between enzymes
  • Like ClCDA, the modeled structure of PgtCDA contains seven alpha-helices and nine beta-sheets, forming an inner-core beta-sheet barrel surrounded by outer-core alpha-helices
  • Upon very long incubation times or when excessive enzyme was added was further and eventually complete deacetylation observed. This is in stark contrast to the results reported for ClCDA, which readily proceeds to complete deacetylation yielding fully deacetylated glucosamine oligomers
  • Recombinant PgtCDA produces partially acetylated chitosan oligosaccharides with a fully defined structure, namely, A-A-deacetylated glucosamine oligomers, a novel pattern that has not been reported so far for chitin deacetylases that produce specific deacetylations

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