Bioconversion of chitosan into chito-oligosaccharides (CHOS) using family 46 chitosanase from Bacillus subtilis (BsCsn46A)

BsCsn46A, a GH family 46 chitosanase from Bacillus subtilis had been previously shown to have potential for bioconversion of chitosan to chito-oligosaccharides (CHOS). However, so far, in-depth analysis of both the mode of action of this enzyme and the composition of its products were lacking. In this study, we have employed size exclusion chromatography, 1H NMR, and mass spectrometry to reveal that BsCsn46A can rapidly cleave chitosans with a wide-variety of acetylation degrees, using a non-processive endo-mode of action. The composition of the product mixtures can be tailored by varying the degree of acetylation of the chitosan and the reaction time. Detailed analysis of product profiles revealed differences compared to other chitosanases. Importantly, BsCsn46A seems to be one of the fastest chitosanases described so far. The detailed analysis of preferred endo-binding modes using H218O showed that a hexameric substrate has three productive binding modes occurring with similar frequencies.