A novel non-hydrolytic protein from Pseudomonas oryzihabitans enhances the enzymatic hydrolysis of cellulose

• A novel cellulase synergistic protein named POEP1 was separated and purified from the culture filtrate of a strain of Pseudomonas oryzihabitans.
• POEP1 was found to have functional similarity to the expansin, expansin-like proteins and LPMOs, but have little sequence similarity according to mass spectrometry analysis.
• The highest synergistic activity was obtained as 364% at the concentration of cellulase 0.1 FPU/g of filter paper.

Several kinds of protein such as the expansin, expansin-like proteins and LPMOs (lytic polysaccharide monooxygenases) are known to exert enhancement effects on cellulase activity. In this study, a novel cellulase synergistic protein named POEP1 was purified from the culture filtrate of Pseudomonas oryzihabitans CGMCC 6169, and was homogeneous on SDS-PAGE with a molecular weight of 60 kDa. Mass spectrometry analysis indicated that it was an unknown protein without sequence similarity to the expansin and expansin-like proteins. Evaluation of the enzymatic hydrolysis of filter paper revealed that POEP1 had no cellulase activity but displayed high synergistic activity of 364% at a cellulase concentration of 0.1 FPU/g of filter paper. When a mixture containing 0.6 FPU cellulase and 700 μg POEP1 per g of cellulose was evaluated, the maximal sugar yield was achieved, which was 2.2-fold greater than that with the cellulase alone. POEP1 was found to have functional similarity to the expansin and expansin-like proteins, which could decrease both the hydrogen-bond intensity and crystallinity, and cause the filter paper disruption. This study provided evidence for the existence of novel bacterial proteins in nature serving the same function as expansin and expansin-like proteins.