3-20: Pretreatment of lignocellulosics using Cel7A: Improving enzymatic hydrolysis rates

The enzymatic hydrolysis of crystalline cellulose encounters various limitations that are both substrate- and enzyme-related. One major feature impeding the activity of the enzymes is the recalcitrance of cellulose to enzymatic attack. Its high crystallinity content appears to be one of the major reasons for overall slow hydrolysis rate, amorphous cellulose being converted more than one order of magnitude faster than crystalline cellulose.

Cel7A cellulose-binding domains (CBDs) were found to produce physical changes in the cellulose structure, which in turn led to higher enzymatic hydrolysis rate upon addition of cellulase cocktail to the reaction mixture.

A protocol was therefore investigated where CBDs were mixed with the substrate (cellulosic or lignocellulosic material), followed by the addition of enzymes to carry out the hydrolysis. The hydrolysis rates obtained thereof were found to be higher than those obtained upon direct addition of cellulases to the substrate. This rate increase was shown to be a combination of hydration effect from the buffer as well as CBD action on cellulose. With lignocellulosic materials, the hydration effect from the buffer was minor so that any gain in rate was directly related to CBDs.