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

A novel β-1,3-glucanase gene (PaBglu50A) from Pseudomonas aeruginosa CAU 342A was cloned and expressed in Escherichia coli. The deduced amino acid sequence of PaBglu50A showed the highest identity of 34% with the β-agarase belonging to glycoside hydrolase (GH) family 50. The purified PaBglu50A had maximal activity at pH 5.5 and 45 °C, respectively. It was stable in the range of pH 4.0-8.0 and at temperatures below 40 °C. The Km and Vmax of PaBglu50A for curdlan and laminarin were 94.4 mg ml−1 and 23.4 μmol min−1 mg−1, 3.65 mg ml−1 and 8.89 μmol 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-β-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 β-1,3-glucanase (EC 3.2.1.39) in GH family 50.