Characterization of a recombinant β-glucosidase of GH3 family from glucosinolate-metabolizing human gut bacterium Enterococcus casseliflavus CP1 for nitrile production

摘要

A recombinant β-glucosidase human gut bacterium capable of nitrile production from desulfo-glucosinolates was studied. The bgl4 gene (2,151 bp) from Enterococcus casseliflavus CP1 was cloned and overexpressed in Escherichia coli BL21(DE3) at 25 °C for 16 h in LB medium using 0.5 mM isopropyl β-D-1-thiogalactopyranoside inducer. The recombinant bgl4 enzyme (79 kDa) was purified using Ni2 affinity column chromatography. This recombinant bgl4 enzyme of the glycosyl hydrolase 3 family did not degrade glucosinolates; however, it transformed desulfo-glucosinolates, except for desulfoglucoraphanin, to produce the corresponding pure nitriles in citrate phosphate buffer pH 7.0 and LB medium. The bgl4 enzyme activity toward pNPG in buffer was optimal at pH 7.0 and 37 °C at 23.4 U/mg, and promoted by Mn2 ; however, activity was slightly deactivated by Fe2 . This provided a possible alternative metabolic route involving nitrile formation from desulfoglucosinolates by β-glucosidase in certain bacteria.