Biochemical characterization of a novel cold-adapted agarotetraose-producing α-agarase, AgaWS5, from Catenovulum...

Although many β-agarases that hydrolyze the β-1,4 linkages of agarose have been biochemically characterized, only three α-agarases that hydrolyze the α-1,3 linkages are reported to date. In this study, a new α-agarase, AgaWS5, from Catenovulum sediminis WS1-A, a new agar-degrading marine bacterium, was biochemically characterized. AgaWS5 belongs to the glycoside hydrolase (GH) 96 family. AgaWS5 consists of 1295 amino acids (140 kDa) and has the 65% identity to an α-agarase, AgaA33, obtained from an agar-degrading bacterium Thalassomonas agarivorans JAMB-A33. AgaWS5 showed the maximum activity at a pH and temperature of 8 and 40 °C, respectively. AgaWS5 showed a cold-tolerance, and it retained more than 40% of its maximum enzymatic activity at 10 °C. AgaWS5 is predicted to have several calcium-binding sites. Thus, its activity was slightly enhanced in the presence of Ca²⁺, and was strongly inhibited by EDTA. The K_m and V_max of AgaWS5 for agarose were 10.6 mg/mL and 714.3 U/mg, respectively. Agarose-liquefication, thin layer chromatography, and mass and NMR spectroscopic analyses demonstrated that AgaWS5 is an endo-type α-agarase that degrades agarose and mainly produces agarotetraose. Thus, in this study, a novel cold-adapted GH96 agarotetraose-producing α-agarase was identified.