Characterization of a novel multi-domain chitinase from alkaliphilic Nocardiopsis sp. strain F96

抄録

Alkaliphilic actinomycete Nocardiopsis sp. strain F96 has been found to produce a single domain glycoside hydrolase (GH) family 18 chitinase (ChiF1). Recently, genome sequencing of strain F96 was completed and three other homologs of GH18 chitinases were found. One of the chitinase homologs, ChiF3, has a multi-domain architecture. The number of domains in ChiF3 is the most various among the four GH18 chitinase homologs. It contained a signal peptide, a carbohydrate-binding module family 2 chitin-binding domain (ChBD), a Fibronectin type Ⅲ-like domain, and a GH18 catalytic domain including a chitinase insertion domain. C-terminally His-tagged ChiF3 was expressed in Escherichia coli, purified and characterized in comparison with ChiF1. Both ChiF1 and ChiF3 showed bimodal pH profiles. Especially, ChiF3 maintained high activity at pH 7.5-9.4 and showed the highest activity at pH 8.5, which is the highest of all the known chitinases from actinomycetes. ChiF3 having ChBD showed higher binding ability toward insoluble chitin compared to ChiF1, which does not have ChBD. Furthermore, the ratio of specific activity of ChiF3 toward insoluble and soluble substrates [Insoluble/Soluble] is 15.2 times higher than that of ChiF1. This difference of substrate preference of both enzymes might be related to the presence or absence of ChBD.