Biochemical characterization of a bilfunctional endoglucanase/glucomannanase derived from mountain soil

Metagenomics is increasingly recognized as a vital technique for exploring uncultured microorganisms, with one key application being the discovery of novel enzymes for industrial use. This study identified an endoglucanase gene from soil metagenome, termed ZFEG1801, which was expressed in E. coli BL21, purified, and characterized for its biochemical properties. The 72.8 kDa recombinant protein exhibited hydrolytic activity against sodium carboxymethyl cellulose (CMC) and konjac glucomannan (KG), with activities of 12.1 U/mg and 42.1 U/mg, respectively. The enzyme displayed optimal activity at pH 5 for CMC and pH 6 for KG, with broad pH stability ranging from 5 to 9. The optimal temperature was 40 °C, and it remained thermally stable between 20 and 40 °C, retaining over 60% of its activity. The enzyme activity remained stable in the presence of most metal ions; however, CMCase activity was inhibited by Cu²⁺, while glucomannanase activity was inhibited by Mn²⁺, Fe³⁺, and Ca²⁺. The catalytic efficiency towards both substrates was reduced by addition of SDS, DMSO, ethanol, isopropanol and acetonitrile. The V_max and K_m of the purified recombinant enzyme were 106.4 μmol/L/min and 4.9 mg/mL for CMC, and 833.3 μmol/L/min and 11.1 mg/mL for KG, respectively. The dual catalytic properties of ZFEG1801, broad pH stability and resistance to additives, demonstrate its potential for use in various biomass degradation processes.