Characterization of a cold-adapted and salt-tolerant exo-chitinase (ChiC) from Pseudoalteromonas sp. DL-6

We have previously reported a non-processive endo-type chitinase, ChiA, from a newly isolated marine psychrophilic bacterium, Pseudoalteromonas sp. DL-6. In this study, a processive exo-type chitinase, ChiC, was cloned from the same bacterium and characterized in detail. ChiC could hydrolyze crystalline chitin into (GlcNAc)₂ as the only observed product. It exhibited high catalytic activity even at low temperatures, e.g. close to 0 °C, or in the presence of 5 M NaCl, suggesting that ChiC was a cold-adapted and highly salt-tolerant chitinase. ChiC could also hydrolyze other substrates, including chitosan and Avicel, indicating its broad substrate specificity. Sequence features indicated that ChiC was a multi-domain protein having a deep substrate-binding groove that was regarded as characteristic of processive exo-chitinases. Enzymatic hydrolysis of chitin by ChiC could be remarkably boosted in the presence of ChiA, suggesting the synergy of ChiC and ChiA. This work provided a new evidence to prove that marine psychrophilic bacteria utilized a synergistic enzyme system to degrade recalcitrant chitin.