Structural and functional studies of the glycoside hydrolase family 3 β-glucosidase Cel3A from the moderately thermophilic fungusRasamsonia emersonii

Abstract

The filamentous fungusHypocrea jecorinaproduces a number of cellulases and hemicellulases that act in a concerted fashion on biomass and degrade it into monomeric or oligomeric sugars. β-Glucosidases are involved in the last step of the degradation of cellulosic biomass and hydrolyse the β-glycosidic linkage between two adjacent molecules in dimers and oligomers of glucose. In this study, it is shown that substituting the β-glucosidase fromH. jecorina(HjCel3A) with the β-glucosidase Cel3A from the thermophilic fungusRasamsonia emersonii(ReCel3A) in enzyme mixtures results in increased efficiency in the saccharification of lignocellulosic materials. Biochemical characterization ofReCel3A, heterologously produced inH. jecorina, reveals a preference for disaccharide substrates over longer gluco-oligosaccharides. Crystallographic studies ofReCel3A revealed a highly N-glycosylated three-domain dimeric protein, as has been observed previously for glycoside hydrolase family 3 β-glucosidases. The increased thermal stability and saccharification yield and the superior biochemical characteristics ofReCel3A compared withHjCel3A and mixtures containingHjCel3A makeReCel3A an excellent candidate for addition to enzyme mixtures designed to operate at higher temperatures.