Enzymatic synthesis of 4-hydroxyphenyl β-D-oligoxylosides and their notable tyrosinase inhibitory activity

Abstract

We have purified and characterized an oligoxylosyl transfer enzyme (OxtA) from Bacillus sp. strain KT12. In the present study, a N-terminally His-tagged recombinant form of the enzyme, OxtA(H)E, was overproduced in Escherichia coli and applied to the reaction with xylan and hydroquinone to produce 4-hydroxyphenyl β-D-oligoxylosides, β-(Xyl)n-HQ (n =1-4), by one step reaction. The obtained β-(Xyl)n-HQ inhibited mushroom tyrosinase, which catalyzes the oxidation of L-DOPA to L-DOPA quinine, and the IC50 values of β-Xyl-HQ, β-(Xyl)2-HQ, β-(Xyl) 3-HQ, and β-(Xyl)4-HQ were 3.0, 0.74, 0.48, and 0.18mM respectively. β-(Xyl)4-HQ showed 35-fold more potent inhibitory activity than β-arbutin (4-hydroxyphenyl β-D- glucopyranoside), of which the IC50 value was measured to be 6.3mM. Kinetic analysis revealed that β-(Xyl)2-HQ, β-(Xyl)3-HQ, and β-(Xyl)4-HQ competitively inhibited the enzyme, and the corresponding Ki values were calculated to be 0.20, 0.29, and 0.057mM respectively.