Biochemical Characterization of Family 7 Cellobiohydrolases from Two Species of Social Amoeba

Enzymatic cocktails for biomass saccharification generally rely on enzymes derived from filamentous fungi such as Trichoderma reesei (Hypocrea jecorina). In T. reesei, the Glycoside Hydrolase Family 7 (GH7) cellobiohydrolase  (Cel7A) is the most abundant component and exhibits the majority of the hydrolytic potential for the conversion of crystalline cellulose to soluble sugars. As GH7 enzymes are central to natural and industrial cellulolytic cocktails, improved understanding of their function is a key to enhancement of biomass conversion processes. To further the understanding of GH7 cellobiohydrolases, we are investigating enzymes recently discovered in genomics studies from relatively obscure organisms. Our ultimate goal is to determine the structural elements leading to activity differences in GH7 cellobiohydrolases, which will aid in the development of structure-activity relationships in these key industrial enzymes. In the current study, we compare GH7 cellulases from two species of social amoebae Dictyostelium discoideum and D. purpureum, with T. reesei Cel7A. Our results show that while these proteins all function optimally in similar biochemical conditions, the Dictyostelium enzymes exhibit slightly lower melting temperatures but have higher activity on 2-nitrophenyl-D-lactose (pNPL) than T. reesei Cel7A. We also report the activity of the D. discoideum and D. purpureum GH7 cellulases on insoluble cellulose at optimal temperatures and contrast their activity and properties with that of T. reesei Cel7A.