A new κ-carrageenase CgkS from marine bacterium Shewanella sp Kz7

A new kappa-carrageenase gene cgkS was cloned from marine bacterium Shewanella sp. Kz7 by using degenerate and site-finding PCR. The gene was comprised of an open reading frame of 1224 bp, encoding 407 amino acid residues, with a signal peptide of 24 residues. Based on the deduced amino acid sequence, the kappa-carrageenase CgkS was classified into the Glycoside Hydrolase family 16. The cgkS gene was expressed in Escherichia coli, and the recombinant enzyme was purified to homogeneity with a specific activity of 716.8 U mg(-1) and a yield of 69%. Recombinant CgkS was most active at 45A degrees C and pH 8.0. It was stable at pH 6.0-9.0 and below 30A degrees C. The enzyme did not require NaCl for activity, although its activity was enhanced by NaCl. CgkS degraded kappa-carrageenan in an endo-fashion releasing tetrasaccharides and disaccharides as main hydrolysis products.