Xylanase from Marine Filamentous Fungus sp. AN-7 Was Activated with Diluted Salt Solution Like Brackish Water.

The genus are endophytic fungi that have recently been identified as cellulolytic system producers. We herein cloned a gene coding for a xylanase belonging to glycoside hydrolase (GH) family 10 (Xyn10A) from sp. AN-7, which was isolated from the soil of a mangrove forest. This protein was heterologously expressed by as a host, and its enzymatic properties were characterized. Xyn10A was produced as a glycosylated protein and coincident to theoretical molecular weight (35.3 kDa) after deglycosylation by peptide--glycosidase F. Purified recombinant Xyn10A exhibited maximal activity at pH 6.0 and 50 °C, and activity was maintained at 90 % at pH 5.0 and temperatures lower than 30 °C for 24 h. The substrate specificity of Xyn10A was limited and it hydrolyzed glucuronoxylan and arabinoxylan, but not β-glucan. The final hydrolysis products from birchwood xylan were xylose, xylobiose, and 1,2-α-D-(4--methyl-glucuronyl)-1,4-β-D-xylotriose. The addition of metallic salts (NaCl, KCl, MgCl, and CaCl) activated Xyn10A for xylan degradation, and maximal activation by these divalent cations was approximately 160 % at a concentration of 5 mM. The thermostability of Xyn10A significantly increased in the presence of 50 mM NaCl or 5 mM MgCl. The present results suggest that the presence of metallic salts at a low concentration, similar to brackish water, exerts positive effects on the enzyme activity and thermal stability of Xyn10A.