Cloning and biochemical characterization of a novel κ-carrageenase from newly isolated marine bacterium Pedobacter hainanensis NJ-02.

Enzymatic preparation of carrageenan oligosaccharides has drawn increasing attention due to its advantages of mild reaction conditions and excellent product-specificity. A novel gene (CgkA) encoding a new κ-carrageenase was cloned, heterogeneously expressed and characterized from a newly isolated marine bacterium Pedobacter hainanensis NJ-02. It consisted of 1539bp and encoded 512 amino acid residues with a molecular weight of 57.12kDa. Multiple alignment analysis indicated that CgkA belongs to glycoside hydrolase (GH) family 16 and was most homologous to κ-carrageenase of Zobellia sp. M-2 with identity of 50%. The recombinant enzyme showed maximal activity of 3659.72U/mg at 40°C and pH 7.0. Additionally, it could retain more than 80% of its maximal activity after being incubated at pH of 5.0-9.0 below 40°C.K+ and Na+ with a wide range of concentration can activate the enzyme, while other divalent ions such as Cu2+ , Zn2+ showed inhibitory effect on the enzyme. The ESI-MS analysis of hydrolysates indicated that the enzyme can endolytically depolymerize the carrageenan into tetrasaccharides and hexasaccharides. The results suggest that it is an endo-type carrageenase and could be a valuable enzyme tool to produce carrageenan oligosaccharides with higher Dps.