A putative glycoside hydrolase family 43 beta-xylosidase/alpha-arabinofuranosidase (CoXyl43) that promotes plant biomass saccharification was isolated via functional screening of a compost microbial metagenomic library and characterized. CoXyl43 promoted the saccharification of plant biomasses, including xylans (xylan and arabinoxylan), rice straw, and Erianthus, by degrading xylooligosaccharide residues to monosaccharide residues. The recombinant CoXyl43 protein exhibited both beta-xylosidase and alpha-arabinofuranosidase activities for chromogenic substrates, with optimal activity at pH 7.5 and 55 A degrees C. Both of these activities were inactivated by ethanol, dimethylsulfoxide, and zinc and copper ions but were activated by manganese ions. Only the beta-xylosidase activity of recombinant CoXyl43 was enhanced in the presence of calcium ions. These results indicate that CoXyl43 exhibits unique enzymatic properties useful for biomass saccharification.