A first glycoside hydrolase family 50 endo-β-1,3-D-glucanase from Pseudomonas aeruginosa

A novel beta-1,3-glucanase gene (PaBglu50A) from Pseudomonas aeruginosa CAU 342A was cloned and expressed in Escherichia coil. The deduced amino acid sequence of PaBglu50A showed the highest identity of 34% with the beta-agarase belonging to glycoside hydrolase (GH) family 50. The purified PaBglu50A had maximal activity at pH 5.5 and 45 degrees C, respectively. It was stable in the range of pH 4.0-8.0 and at temperatures below 40 degrees C. The K-m and V-max of PaBglu50A for curdlan and laminarin were 94.4 mg ml(-1) and 23.4 mu mol min(-1) mg(-1), 3.65 mg ml(-1) and 8.89 mu mol min(-1) mg(-1), respectively. All characterized members of GH family 50 were only active towards agarose so far. However, the recombinant protein PaBglu50A did not display activity towards agarose but showed activity towards water-insoluble curdlan and laminarin. The hydrolysis products for curdlan supported this protein to be an endo-beta-1,3-glucanase, making a significant difference from the reported enzymes of GH family 50. These results suggested that PaBglu50A is the first endo-type beta-1,3-glucanase (EC 3.2.1.39) in GH family 50.