Paenibacillus polymyxa exhibits remarkable hemicellulolytic activity. In the present study, 13 hemicellulose-degrading enzymes were identified from the secreted proteome of P. polymyxa KF-1 by liquid chromatography-tandem mass spectrometry analysis. α-L-arabinofuranosidase is an important member of hemicellulose-degrading enzymes. A novel α-L-arabinofuranosidase (PpAbf51b), belonging to glycoside hydrolase family 51, was identified from P. polymyxa. Recombinant PpAbf51b was produced in Escherichia coli BL21 (DE3) and was found to be a tetramer using gel filtration chromatography. PpAbf51b hydrolyzed neutral arabinose-containing polysaccharides, including sugar beet arabinan, linear-1,5-α-L-arabinan, and wheat arabinoxylan, with L-arabinose as the main product. The products from hydrolysis indicate that PpAbf51b functions as an exo-α-L-arabinofuranosidase. Combining PpAbf51b and Trichoderma longibrachiatum endo-1,4-xylanase produced significant synergistic effects for the degradation of wheat arabinoxylan. The α-L-arabinofuranosidase identified from the secretome of P. polymyxa KF-1 is potentially suitable for application in biotechnological industries.

Microbial lytic polysaccharide monooxygenases (LPMOs) catalyze the oxidative cleavage of crystalline polysaccharides including chitin and cellulose. The discovery of a large assortment of LPMO-like proteins widely distributed in insect genomes suggests that they could be involved in assisting chitin degradation in the exoskeleton, tracheae and peritrophic matrix during development. However, the physiological functions of insect LPMO-like proteins are still undetermined. To investigate the functions of insect LPMO subgroup I-like proteins, which contain an AA15 LPMO catalytic domain and a conserved C-terminal cysteine-rich motif, two evolutionarily distant species, Tribolium castaneum and Locusta migratoria, were chosen for study. RNAi for the T. castaneum protein, TcLPMO1, caused molting arrest at all developmental stages, whereas RNAi of the L. migratoria protein, LmLPMO1, prevented only adult eclosion. In both species, LPMO1-deficient animals were unable to shed their exuviae and died. TEM analysis revealed failure of turnover of chitinous cuticle, which is critical for completion of molting. Purified recombinant LPMO1-like protein from Ostrinia furnacalis (rOfLPMO1) exhibited oxidative cleavage activity and substrate preference for chitin. These results reveal for the first time the physiological importance of catalytically active LPMO1-like proteins from distant insect species and provide new insight into the enzymatic mechanism of chitin turnover during molting.