The first characterization of a Ca2+-dependent carbohydrate-binding module of β-1,3-xylanase from Flammeovirga pacifica.

A novel carbohydrate binding module (CBM) was identified in a β-1,3-xylanase from Flammeovirga pacifica, which showed only 25.0% sequence identity with the reported CBMs with the coverage of 36.4%. To verify its function, a truncated β-1,3-xylanase (Xy13088-T) and a carbohydrate binding module (CBM3088) were expressed and purified. The thermostability and catalytic efficiency of the Xy13088-T declined significantly when compared with the full-length one, with the decreasing of the half-life and catalytic efficiency (Kcat/Km) by 90%. Interestingly, the CBM3088 showed the binding ability to β-1,3-xylan only when Ca2+ existed, which was different from the reported CBMs of β-1,3-xylanases. The maximum amount of CBM3088 binding to β-1,3-xylan was 9.65 μmol/g of β-1,3-xylan. The residues probably involved in the binding to the β-1,3-xylan and Ca2+ were addressed by bioinformatics analysis.