Glycoside Hydrolase Family 39 β-Xylosidase of Sphingomonas Showing Salt/Ethanol/Trypsin Tolerance, Low-pH/Low-Temperature Activity, and Transxylosylation Activity

Mining for novel enzymes from new microorganisms is a way to obtain β-xylosidases with promising applications. A Sphingomonas β-xylosidase was expressed in Escherichia coli. The purified recombinant enzyme (rJB13GH39) was most active at pH 4.5 and 50 °C, retaining 10%-50% of its maximum activity at 0-20 °C. Most salts and chemical reagents including 3.0%-20.0% (w/v) NaCl showed little or no effect on the enzymatic activity. rJB13GH39 exhibited 71.9% and 55.2% activity in 10.0% and 15.0% (v/v) ethanol, respectively. rJB13GH39 was stable below 60 °C in 3.0%-30.0% (w/v) NaCl, 3.0%-20.0% (v/v) ethanol, and 2.2-87.0 mg/mL trypsin. The enzyme transferred one xylosyl moiety to certain sugars and alcohols. The salt/ethanol tolerance and low-temperature activity of the enzyme may be attributed to its high structural flexibility caused by high proportions of small amino acids ACDGNSTV and random coils.