Trp residue at subsite - 5 plays a critical role in the substrate binding of two protistan GH26 β-mannanases from a termite hindgut.

Symbiotic protists in the hindgut of termites provide a novel enzymatic resource for efficient lignocellulytic degradation of plant biomass. In this study, two β-mannanases, RsMan26A and RsMan26B, from a symbiotic protist community of the lower termite, Reticulitermes speratus, were successfully expressed in the methylotrophic yeast, Pichia pastoris. Biochemical characterization experiments demonstrated that both RsMan26A and RsMan26B are endo-acting enzymes and have a very similar substrate specificity, displaying a higher catalytic efficiency to galactomannan from locust bean gum (LBG) and glucomannan than to β-1,4-mannan and highly substituted galactomannan from guar gum.