Biochemical characterization and crystal structure of a fungal glycoside hydrolase family 3 β-glucosidase, Cel3A from Hypocrea jecorina

β-glucosidases hydrolyze a β-linkage between two adjacent glucose molecules. The most abundant β-glucosidase in the mesophilic fungus Hypocrea jecorina is Cel3A (HjCel3A). We show in this paper that increased levels of HjCel3A in a cellulase mixture produced by H. jecorina improve saccharification of lignocellulosic biomass for the production of biofuels. In addition, we present structures of HjCel3A from enzymes produced either in H. jecorina or Pichia pastoris (pp-HjCel3A), with and without glucose complexed in the active site. The HjCel3A structure has a three-domain architecture, as previously observed for two other GH family 3 β-glucosidases. Biochemical characterization of HjCel3A shows that the enzyme is efficient for hydrolysis of (1,4)- as well as (1,2)-, (1,3)-, and (1,6)- β-D linked disaccharides. Both HjCel3A structures have N-linked glycosylation at Asn208 and Asn310. In HjCel3A a single GlucNac is present at both sites, while in the pp-HjCel3A structure the glycan chains consist of 8 or 4 saccharides, respectively. In both HjCel3A and pp-HjCel3A the glycosylations are involved in intermolecular contacts. Due to the different lengths of the glycosylations, the interactions result in different crystal forms for the two protein forms.