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Functional characterization of a noncatalytic protein, Athe_0181, from Caldicellulosiruptor bescii in promoting lignocellulose hydrolysis

Caldicellulosiruptor bescii is a cellulolytic bacterium that secretes multifunctional glycoside hydrolases for efficient hydrolysis of lignocellulose into fermentable sugars. Additionally, some abundant noncatalytic proteins accompanying multifunctional glycoside hydrolases are also secreted by C. bescii, but its function has not yet been demonstrated. In this study, noncatalytic protein Athe_0181 and multifunctional glycoside hydrolases CbMan5C/Cel5A were expressed and purified from Escherichia coli BL21(DE3). Effective binding capacity of Athe_0181 to lignocellulose was displayed, and it showed preferential affinity to rice straw. Athe_0181 was shown to be a cellulase synergistic protein. It exhibited high synergistic activity of 523% in the presence of 25 μg/mL of CbMan5C/Cel5A with microcrystalline cellulose as the substrate. The structure-modifying activity of Athe_0181 to microcrystalline cellulose was demonstrated by scanning electron microscopy and X-ray diffraction analysis. These characteristics demonstrated that Athe_0181 played a role in the synergism of glycoside hydrolases from C. bescii for efficient hydrolysis of lignocellulose.