kappa-carrageenan oligosaccharides exhibit various biological activities. Enzymatic degradation by kappa-carrageenase is safe and controllable. Therefore, kappa-carrageenases have captured more and more attentions. In this study, a kappa-carrageenase encoding gene, cgkX, was cloned from Pseudoalteromonas sp. QY203 with degenerate and inverse PCR. It comprised an ORF of 1194 bp in length, encoding a protein with 397 amino acid residues. CgkX is a new member of glycoside hydrolase family 16. The deduced amino acid sequence shared a high similarity with CgkX of Pseudoalteromonas kappa-carrageenase; however, the recombinant CgkX showed different biochemical characteristics. The recombinant enzyme was most active at pH 7.0 and 55A degrees C in the presence of 300 mmol L-1 NaCl. It was stable in a broad range of acidity ranging from pH 3.0 to pH 10.0 when temperature was below 40A degrees C. More than 80% of its activity was maintained after being incubated at pH 3.6-10.0 and 4A degrees C for 24 h. CgkX retained more than 90% of activity after being incubated at 40A degrees C for 1 h. EDTA and SDS (1 mmol L-1) did not inhibit its activity. CgkX hydrolyzed kappa-carrageenan into disaccharide and tetrasaccharide as an endo-cleaver. All these characteristics demonstrated that CgkX is applicable to both kappa-carrageenan oligosaccharide production and kappa-carrageenase structure-function research.
