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Publication Abstract from PubMed

Glycoside Hydrolase Family 7 (GH7) cellobiohydrolases (CBHs) are commonly employed enzymes in plant cell wall degradation across eukaryotic kingdoms of life, as they provide significant hydrolytic potential in cellulose turnover. To date, many fungal GH7 CBHs have been examined, yet many questions remain regarding structure-activity relationships in these important natural and commercial enzymes. Here, we present crystal structures and biochemical analysis of two GH7 CBHs from social amoeba:Dictyostelium discoideumandDictyostelium purpureum (DdiCel7A andDpuCel7A, respectively).DdiCel7A andDpuCel7A natively consist of a catalytic domain and do not exhibit a carbohydrate-binding module (CBM). The structures, resolved to 2.1 A (DdiCel7A), and 2.7 A (DpuCel7A), are homologous to other GH7 CBHs with an enclosed active site tunnel. Two primary differences between theDictyosteliumCBHs and the archetypal model GH7 CBH fromTrichoderma reeseiCel7A (TreCel7A) occur near the hydrolytic active site and the product binding sites. To compare the activity of these enzymes withTreCel7A, the Family 1TreCel7A CBM and linker was added to theC-terminus of theDictyosteliumenzymes,DdiCel7ACBMandDpuCel7ACBM, which were recombinantly expressed inT. reeseiDdiCel7ACBMandDpuCel7ACBMhydrolyze Avicel, pretreated corn stover, and phosphoric acid swollen cellulose as efficiently asTreCel7A when compared at their temperature optima. TheKiof cellobiose is significantly higher forDdiCel7ACBMandDpuCel7ACBMthan forTreCel7A: 205, 130, and 29 muM, respectively. Taken together, the present study highlights the remarkable conservation in the activity of these key natural and industrial enzymes across quite distant phylogenetic trees of life. IMPORTANCE: GH7 CBHs are among the most important cellulolytic enzymes both in nature and for emerging industrial applications in cellulose breakdown. Understanding the diversity of these key industrial enzymes is critical to engineering them for higher activity and stability. The present work demonstrates that two GH7 CBHs from social amoeba are surprisingly quite similar in structure and activity to the canonical GH7 CBH from the model biomass-degrading fungus,T. reesei, when tested in equivalent conditions (with added CBM-linker domains) and on an industrially relevant substrate.

Biochemical and structural characterization of two Dictyostelium cellobiohydrolases from the Amoebozoa kingdom reveal a high conservation between distant phylogenetic trees of life.,Hobdey SE, Knott BC, Haddad Momeni M, Taylor LE 2nd, Borisova AS, Podkaminer KK, VanderWall TA, Himmel ME, Decker SR, Beckham GT, Stahlberg J Appl Environ Microbiol. 2016 Apr 1. pii: AEM.00163-16. PMID:27037126^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.