Inhibition of Trichoderma cellulase activity by a stilbene glucoside from Picea glehnii bark

Abstract

The stilbene glucoside isorhapontin (5,4′-dihydroxy-3′- methoxystilbene-3-β-D-glucoside) is the major constituent of the ethyl acetate extracts from Picea glehnii bark. Isorhapontin inhibited the hydrolytic activity of Trichoderma cellobiohydrolase I (CBH I) for both bacterial microcrystalline cellulose and the soluble cellooligosaccharide celloheptaitol. The inhibitory effect for celloheptaitol, however, was more drastic than that for bacterial microcrystalline cellulose. The hydrolytic activity of the CBHI core domain for celloheptaitol was also inhibited by isorhapontin to a similar extent, suggesting that the interaction between isorhapontin and the core domain of CBHI is the reason for this phenomenon. The inhibition of CBHI activity by isorhapontin showed mixed noncompetitive and uncompetitive types in a concentration of the inhibitor of less than 125 μM. The Ki and Ki′ values were estimated to be 57.2 and 33.3 μM respectively. Whereas isorhapontin strongly inhibited CBH I activity, its aglycone isorhapontigenin (3′-methoxy-3,5,4′-trihydroxystilbene) showed almost no inhibition. Consequently, both the stilbenic and the β-glucosidic structures in isorhapontin are essential for the inhibitory effect on CBH I activity. Isorhapontin also inhibited the activity of Trichoderma endoglucanase I for celloheptaitol, whereas almost no effect was observed for the activities of both endoglucanases II and III.