A β-agarase with high pH stability from Flammeovirga sp. SJP92

• A novel endo-type β-agarase gene was cloned and characterized.
• AgaB is a GH16 β-agarase with high pH stability.
• AgaB has a high affinity for agarose.
• AgaB could tolerate a high concentration of denaturants.
• The enzymatic activity of AgaB can be enhanced by more than 60% by β-Mercaptoethanol.

A novel endo-type β-agarase, AgaB, was cloned from an agar-degrading bacterium, Flammeovirga sp. SJP92. The gene agaB consists of 2, 550 bp and encodes a protein of 849 amino acids including a 19 amino acids signal peptide. Based on the amino acid sequence similarity, AgaB belongs to the glycoside hydrolase family GH16. The recombinant AgaB was expressed in Escherichia coli and exhibited maximal activity at around 45 °C and pH 8.0, with a specific activity of 254.2 U/mg, a Km of 3.99 mg/ml and a Vmax of 700 U/mg for agarose. The agarase was stable at neutral to mildly alkaline condition, and remained 85%–90% of activity after treatment for 1 h, a characteristic much more different from other agarases reported. The recombinant enzyme was sensitive to some metal ions (Cu2+, Co2+ and Zn2+), but resistant to some denaturants (urea and SDS). It can hydrolyze the β-1, 4-glycosidic linkages of agarose, yielding neoagarotetraose and neoagarohexaose as the main products. These properties could make AgaB has a potential application in the food, cosmetic and medical industries.

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