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A GHF7 CELLULASE FROM THE PROTIST SYMBIONT COMMUNITY OF Reticulitermes flavipes ENABLES MORE EFFICIENT LIGNOCELLULOSE PROCESSING BY HOST ENZYMES
Author(s) -
Sethi Amit,
Kovaleva Elena S.,
Slack Jeffrey M.,
Brown Susan,
Buchman George W.,
Scharf Michael E.
Publication year - 2013
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/arch.21135
Subject(s) - reticulitermes , cellulase , biology , protist , host (biology) , enzyme , rhinotermitidae , microbiology and biotechnology , botany , ecology , biochemistry , gene
Termites and their gut microbial symbionts efficiently degrade lignocellulose into fermentable monosaccharides. This study examined three glycosyl hydrolase family 7 ( GHF 7) cellulases from protist symbionts of the termite R eticulitermes flavipes . We tested the hypotheses that three GHF 7 cellulases ( GHF 7‐3 , GHF 7‐5 , and GHF 7‐6 ) can function synergistically with three host digestive enzymes and a fungal cellulase preparation. Full‐length c DNA sequences of the three GHF 7s were assembled and their protist origins confirmed through a combination of quantitative PCR and cellobiohydrolase ( CBH ) activity assays. Recombinant versions of the three GHF 7s were generated using a baculovirus‐insect expression system and their activity toward several model substrates compared with and without metallic cofactors. GHF 7‐3 was the most active of the three cellulases; it exhibited a combination of CBH , endoglucanase ( EG ase), and β‐glucosidase activities that were optimal around pH 7 and 30°C, and enhanced by calcium chloride and zinc sulfate. Lignocellulose saccharification assays were then done using various combinations of the three GHF 7s along with a host EG ase ( C ell‐1 ), beta‐glucosidase ( β‐glu ), and laccase ( LacA ). GHF 7‐3 was the only GHF 7 to enhance glucose release by Cell‐1 and β‐glu. Finally, GHF 7‐3, C ell‐1, and β‐glu were individually tested with a commercial fungal cellulase preparation in lignocellulose saccharification assays, but only β‐glu appreciably enhanced glucose release. Our hypothesis that protist GHF 7 cellulases are capable of synergistic interactions with host termite digestive enzymes is supported only in the case of GHF 7‐3. These findings suggest that not all protist cellulases will enhance saccharification by cocktails of other termite or fungal lignocellulases.