Characterization of Thermotoga thermarum DSM 5069 α-glucuronidase and synergistic degradation of xylan

Abstract

α-Glucuronidases are capable of breaking down the α-1,2-glycosidic bonds of 4-O-methyl-D-glucuronic acid residues. As an accessory enzyme, α-glucuronidase plays a vital role in xylan degradation. The recombinant α-glucuronidase from Thermotoga thermarum DSM 5069 was heterologously expressed in the Escherichia coli system, purified, and characterized. The purified enzyme exhibited optimal activity toward aldouronic acids at pH 6.5 and 80 °C. It was fairly thermostable and maintained 98% residual activity after incubation at 65 °C for 2.0 h. The kinetic parameters Km, Vmax, and kcat were 3.02 ± 0.16 mM, 88 ± 2 μmol min-1 mg-1, and 117 s-1, respectively. TtAguA had an apparent activation energy of 59.0 kJ/mol. By structure simulation and mutation analyses, Glu288 was identified as the catalytic proton donor, and Asp367 and Glu395 were likely nucleophile bases. The xylan degradation by endoxylanase Xyn10A was enhanced by approximately 10% in the presence of TtAguA.