Objectives: Chitinases play important role in chitin bioconversion, while few of them have been put into use due to their poor properties. We aimed to identify and characterize chitinases suitable for N-acetyl chitooligosaccharides (COSs) production from chitin materials.
Results: A chitinase gene (SsChi28) from Streptomyces sampsonii XY2-7 was cloned and heterologously expressed in E. coli BL21 (DE3) as an active protein. The deduced protein shared high sequence identities and structure similarities with some glycoside hydrolase family 19 chitinases. The recombinant enzyme (SsChi28) was purified and biochemically characterized. SsChi28 was a monomeric protein with a molecular mass of 30 kDa estimated by SDS-PAGE. It was most active at pH 6.0 and 55 °C, respectively, and stable in a wide pH range of 3.5-11.5 and up to 60 °C. The enzyme exhibited strict substrate specificities towards ethylene glycol chitin (222.3 U/mg) and colloidal chitin (20.1 U/mg). Besides, it displayed lysozyme activity against Micrococcus lysodeikticus. SsChi28 hydrolyzed colloidal chitin to yield mainly N-acetyl chitobiose, accounting high up to 73% (w/w) in total products.
Conclusion: The excellent enzymatic properties of SsChi28 may make it potential in chitin bioconversion (especially for N-acetyl COS production), as well as in biological control of fungal diseases.
Keywords: Chitinase; Gene cloning; Lysozyme activity; N-acetyl chitibiose; Streptomyces sampsonii.