Abstact

The pursuit of sustainable energy has intensified the search for efficient biocatalysts to convert lignocellulosic biomass. In this context, we characterized a novel bifunctional enzyme, TerARA, identified from the gut metagenome of the termite Pseudacanthotermes militaris. Belonging to the glycoside hydrolase 43 (GH43) family, TerARA was heterologously expressed in E. coli BL21 and purified. The enzyme demonstrated bifunctional activity toward synthetic substrates p-nitrophenyl-α-L-arabinofuranoside (pNP-Araf) (387.22 ± 74.2 U/mg) and p-nitrophenyl-β-D-xylopyranoside (pNP-Xyl) (330.82 ± 31.2 U/mg), with higher catalytic efficiency for pNP-Araf (9.14 s-1·mM-1), suggesting functional preference as an α-L-arabinofuranosidase. Activity modulation by metal ions revealed that Ca2+ slightly improved efficiency toward pNP-Araf (to 9.58 s-1·mM-1 at 1 mM), while Zn2+ reduced efficiency for pNP-Xyl except at 5 mM (6.65 s-1·mM-1). Zn2+ also enhanced enzymatic stability, maintaining 80 % activity in pNP-Xyl hydrolysis. Crystallographic analysis at 2.0 Å resolution revealed a 43 Glycosyl Hydrolase catalytic domain with a five-bladed β-propeller fold and two Ca2+ ions and a Carbohydrate-Binding Module (CBM) domain with a β-sandwich fold likely involved in substrate interaction. Conserved catalytic residues, binding sites, and Ca2+ stabilizing effects were identified. TerARA's bifunctionality and structural features support its application in hemicellulose degradation and biomass conversion.