Biochemical Characterization and Substrate Degradation Mode of a Novel Exotype β-Agarase from Agarivorans gilvus WH0801

Agarases are important hydrolytic enzymes for the biodegradation of agar. Understanding the degradation mode and hydrolysis products of agarases is essential for their utilization in oligosaccharide preparations. Herein, we cloned and expressed AgWH50B, a novel neoagarotetraose-forming β-agarase from Agarivorans gilvus WH0801 that has high specific activity and a fast reaction rate. AgWH50B consists of a C-terminal glycoside hydrolase family 50 catalytic domain with two tandem noncatalytic carbohydrate-binding modules (CBMs) in the N-terminus (residues 45-214 and 236-442). AgWH50B exhibited good enzymatic properties with high specific activity and catalytic efficiency (1523.2 U/mg and a V_max of 1700 μmol/min/mg) under optimal hydrolysis conditions of pH 7.0 and 40 °C. Analysis of the hydrolysis products revealed that this enzyme is an exotype β-agarase and that the dominant product of agarose or oligosaccharide degradation was neoagarotetraose. These findings suggest that AgWH50B could be utilized to yield abundant neoagarotetraose.