Specific hydrolysis of curdlan with a novel glycoside hydrolase family 128 β-1,3-endoglucanase containing a carbohydrate-binding module.

The cbm6e gene from Saccharophagus degradans 2-40 was cloned and expressed in Escherichia coli. CBM6E contains a glycoside hydrolase family 128 (GH128) catalytic module and a C-terminal carbohydrate-binding module (CBM) grouped into CBM family 6. The purified recombinant CBM6E displayed high substrate specificity toward curdlan as an endo-β-1,3-glucanase and had maximal activity at pH 6.0 and 35 ℃. The hydrolytic products against curdlan were predominantly laminaritriose (L3) and laminaritetraose (L4) along with a lower amount of laminaripentaose (L5) and laminarihexaose (L6). The CBM6 module selectively enhanced the enzyme activity against curdlan and displayed strict binding specificity to curdlan, no matter in its powder or high-set gel forms. This study laid a foundation for enzymatic degradation of curdlan to produce high-value β-1,3-glucooligosaccharides at moderate temperatures and provided a novel CBM tag for enzyme immobilization on curdlan.