Enzyme and Microbial Technology, Vol.96, 75-84, 2017
The family 22 carbohydrate-binding module of bifunctional xylanase/beta-glucanase Xyn10E from Paenibacillus curdlanolyticus B-6 has an important role in lignocellulose degradation
A newly isolated endo-beta-1,4-xylanase (Xyn10E) from Paenibacillus curdlanolyticus B-6 has a modular structure consisting of a family 22 carbohydrate-binding module (CBM), a glycoside hydrolase (GH) family 10 catalytic domain, two fibronectin type III (Fn3) domains, and a family 3 CBM at the C-terminus. Intact Xyn10E (rXyn10E), CBM22-deleted Xyn10E (X-CBM3), CBM3-deleted Xyn10E (X-CBM22), and GH10 catalytic domain only (X-GH10) were expressed in Escherichia coli. rXyn 10E showed bifunctional degradation activity toward xylan and beta-glucan and also degraded microcrystalline cellulose. Although X-CBM3 and X-GH10 had drastically reduced xylanase and beta-glucanase activities, X-CBM22 mostly retained these activities. Similar K. values were obtained for rXyn 10E and X-CBM3, but k(cat) and k(cat)/K-m values for X-CBM3 and X-GH10 were lower than those for rXyn 10E, suggesting that CBM22 of Xyn10E may contribute to catalytic efficiency. In binding assays, X-CBM3 was still able to bind to 8-glucan, soluble xylan, insoluble xylan, and cellulose through GH10 and CBM3. These results indicate that CBM22 has an important role not only in binding to xylan and 8-glucan but also in feeding both polysaccharides into the neighboring GH10 catalytic domain, rXyn10E showed remarkable synergism with rXyn1 1A, a major xylanase subunit of P. curdlanolyticus B-6, in the degradation of untreated corn stover and sugarcane bagasse; however, the combination of X-CBM3 and rXynl 1A was not synergistic. These results indicate that Xyn10E and Xyn11A act synergistically on lignocellulosic biomass, and CBM22 is essential for efficient degradation of lignocellulosic materials. (C) 2016 Elsevier Inc. All rights reserved.