Expression and Biochemical Characterization of a Novel Marine Chitosanase from Streptomyces niveus Suitable for Preparation of Chitobiose

It is known that bioactivities of chitooligosaccharide (COS) are closely related to the degree of polymerization (DP); therefore, it is essential to prepare COS with controllable DP, such as chitobiose showing high antioxidant and antihyperlipidemia activities. In this study, BLAST, sequence alignment and phylogenetic analysis of characterized glycoside hydrolase (GH) 46 endo-chitosanases revealed that a chitosanase Sn1-CSN from Streptomyces niveus was different from others. Sn1-CSN was overexpressed in E. coli, purified and characterized in detail. It showed the highest activity at pH 6.0 and exhibited superior stability between pH 4.0 and pH 11.0. Sn1-CSN displayed the highest activity at 50 degrees C and was fairly stable at <= 45 degrees C. Its apparent kinetic parameters against chitosan (DDA: degree of deacetylation, >94%) were determined, with K-m and k(cat) values of 1.8 mg/mL and 88.3 s(-1), respectively. Cu2+ enhanced the activity of Sn1-CSN by 54.2%, whereas Fe3+ inhibited activity by 15.1%. Hydrolysis products of chitosan (DDA > 94%) by Sn1-CSN were mainly composed of chitobiose (87.3%), whereas partially acetylated chitosan with DDA 69% was mainly converted into partially acetylated COS with DP 2-13. This endo-chitosanase has great potential to be used for the preparation of chitobiose and partially acetylated COS with different DPs.

Automated summary

This study focused on characterizing the glycoside hydrolase Sn1-CSN from Streptomyces niveus, which showed high enzymatic activity towards chitosan with excellent stability under various pH and temperature conditions. Sn1-CSN demonstrated the potential to hydrolyze chitosan to produce chitobiose and partially acetylated COS with different degrees of polymerization, indicating its usefulness in preparing COS with controllable DP.