Role of fibronectin type III domain in enhancing the substrate accessibility of modular GH9 endocellulase by reducing non-specific binding to lignin

Utilizing lignocellulosic biomass effectively can lessen reliance on fossil fuels and facilitate the production of second-generation biorefinery feedstocks. The nonspecific binding of lignin to cellulases is one of the main factors affecting their enzymatic performance and hampering their efficiency in degrading lignocellulose. Processive endocellulase from Acidothermus cellulolyticus 11B has a modular structure consisting of several carbohydrate-binding modules, a glycoside hydrolase family 9 catalytic domain, and a fibronectin type III (FN3) domain. This study investigated the role of the FN3 in the degradation of lignocellulose by constructing multiple mutants. The results showed that the FN3 could improve the thermal stability of the enzyme and resist the nonspecific binding of lignin to cellulase. This characteristic can significantly increase the lignocellulose's enzymatic efficiency and offer a novel approach to the artificial design of multi-modular cellulases.