Functional characterization of a superoxide dismutase and a lytic polysaccharide monooxygenase AA10 from the lower termite Coptotermes gestroi

Termites are considered to be efficient decomposers in nature converting lignocellulosic biomass with 65-90% of efficiency. This is possible due to termites and their symbionts, which have a repertoire of Cazymes that act in conjunction with oxidoreductases to breakdown lignocellulose. RNA-Seq analysis of the termite C.gestroi revealed the occurrence of superoxide dismutases-(SOD) CgSOD-1 and a putative lytic polysaccharide monooxygenases-(LPMO-AA10) CgAA10-2. Both genes had high abundance of transcripts when C.gestroi was fed with pretreated sugarcane-bagasse (rich in cellulose and lignin). Aiming at investigating the role of these enzymes in the metabolism of C. gestroi, CgSOD-1 and CgAA10-2 were cloned and heterologously expressed in E.coli. After purification, the enzymes were characterized. CgSOD1 exhibited a synergism with an endoglucanase-GHF9 in ß-glucan hydrolysis. CgSOD1 was also able to enhance the hydrolysis of steam-exploded sugarcane bagasse acting in conjunction with commercial cellulases cocktail. The HPAEC-PAD analysis found that CgSOD1 released oligosaccharides from ß-glucan, and biochemical assays suggested the generation of hydroxyl radicals to depolymerize this polysaccharide. CgAA10-2 is, to the best of our knowledge, the first LPMO described from animals, after further phylogenetic analysis. Biochemical assays using amplex red protocol reported pH8 as optimum, and temperature stability of 75ºC. HPAEC-PAD analysis showed that this enzyme released oxidized sugars from PASC at pH6 and pH8 using ascorbate as reductant. Further studies are required such as the immunolocalization of theses enzymes in C.gestroi’s gut, a microoxic environment. In conclusion, the results suggested that both enzymes could play a role in lignocellulose degradation by C. gestroi.