Cloning, expression, biochemical characterization, and molecular docking studies of a novel glucose tolerant β-glucosidase from Saccharomonospora sp. NB11

Most of the presently known β-glucosidases are sensitive to end-product inhibition by glucose, restricting their potential use in many industrial applications. Identification of novel glucose tolerant β-glucosidase can prove a pivotal solution to eliminate end-product inhibition and enhance the overall lignocellulosic saccharification process. In this study, a novel gene encoding β-glucosidase BglNB11 of 1405bp was identified in the genome of Saccharomonospora sp. NB11 and was successfully cloned and heterologously expressed in E. coli BL21 (DE3).The presence of conserved amino acids; NEPW and TENG indicated that BglNB11 belonged to GH1 β-glucosidases. The recombinant enzyme was purified using a Ni-NTA column, with the molecular mass of 51 kDa, using SDS-PAGE analysis. BglNB11 showed optimum activity at 40 °C and pH 7 and did not require any tested co-factors for activation. The kinetic values, K_m, V_max, k_cat, and k_cat/K_m of purified enzyme were 0.4037 mM, 5735.8 μmol/min/mg, 5042.16 s^-1 and 12487.71 s^-1 mM^-1, respectively. The enzyme was not inhibited by glucose to a concentration of 4 M but was slightly stimulated in the presence of glucose. Molecular docking of BglNB11 with glucose suggested that the relative binding position of glucose in the active site channel might be responsible for modulating end product tolerance and stimulation. β-glucosidase from BglNB11 is an excellent enzyme with high catalytic efficiency and enhanced glucose tolerance compared to many known glucose tolerant β-glucosidases. These unique properties of BglNB11 make it a prime candidate to be utilized in many biotechnological applications.