Molecular Cloning, Expression and Biochemical Characterization of a Family 5 Glycoside Hydrolase First Endo-Mannanase (RfGH5_7) from Ruminococcus flavefaciens FD-1 v3

The cellulosomal enzyme, Rf GH5 1/2 , of Ruminococcus flavefaciens contains an N-terminal module, a family 5 glycoside hydrolase GH5_4 with a putative endoglucanase activity, while C-terminal domain is a putative endo-mannanase (GH5_7). The two putative catalytic modules are separated by family 80 carbohydrate binding module (CBM80) having wide ligand specificity. The putative endo-mannanase module, GH5_7 ( Rf GH5_7), was cloned, expressed in Escherichia coli BL-21(DE3) cells and purified. SDS-PAGE analysis of purified Rf GH5_7 showed molecular size ~ 35 kDa. Substrate specificity analysis of Rf GH5_7 showed maximum activity against locust bean galactomannan (298.5 U/mg) followed by konjac glucomannan (256.2 U/mg) and carob galactomannan (177.2 U/mg). Rf GH5_7 showed maximum activity at optimum pH 6.0 and temperature 60 °C. Rf GH5_7 displayed stability in between pH 6.0 and 9.0 and thermostability till 50 °C. 10 mM Ca 2+ ions increased the enzyme activity by 33%. The melting temperature of Rf GH5_7 was 84 °C that was not affected by Ca 2+ ions or chelating agents. Rf GH5_7 showed, V max , 389 U/mg and K m , 0.92 mg/mL for locust bean galactomannan. TLC analysis revealed that Rf GH5_7 hydrolysed locust bean galactomannan predominantly to mannose, mannobiose, mannotriose and higher degree of polymerization of manno-oligosaccharides indicating an endo-acting catalytic mechanism. This study revealed a highly active and thermostable endo-mannanase with considerable biotechnological potential.