title: The binding, synergistic and structural characteristics of BsEXLX1 for loosening the main components of lignocellulose: Lignin, xylan, and cellulose.
abstract: The bacterial expansin, BsEXLX1, has been studied as a model to understand the synergistic effect of expansins on lignocellulose degradation and the structure-function relationships of expansins. However, the specific mechanism is still poorly understood. In this study, the binding, synergistic and structural characteristics of BsEXLX1 for loosening the main components of lignocellulose: lignin, xylan, and cellulose, were further characterized. Results showed that BsEXLX1 preferentially binds to xylan over lignin or cellulose under various conditions. The binding of BsEXLX1 to all substrates increased linearly with the initial concentration of BsEXLX1. But the changing rate of binding (i.e., slope of the line; k value) varied with the incubation temperature. Interestingly, the binding of BsEXLX1 to substrates did not saturate. Mutating residue-125, 126 or 171 indicated their importance for binding, but they were less important for binding to xylan. Through binding assays and homologous modeling, it was concluded that residue-125 and 171 play more important roles in the structural maintenance of BsEXLX1. By comparing the synergistic activity of BsEXLX1 or its mutants, it was found that synergistic activity is not correlated with specific binding. All these results can lead deeper understand about the mechanism of wall loosening by expansins, and further promote the application of expansins in lignocellulose degradation.
authors.affiliation: Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, 310058, China.
authors.forename: Qun
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Zhejiang Gongshang University, Hangzhou 310018, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.affiliation: Institute of Environment Resource and Soil Fertilizer, Zhejiang Academy of Agriculture Science, Hangzhou 310021, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Lin
authors.affiliation: School of Forestry and Biotechnology, Zhejiang Agriculture and Forestry University, 311300 Lin an, Zhejiang, China.
authors.forename: Daobing
authors.initials: D
authors.lastname: Yu
authors.affiliation: Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, 310058, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Shen
authors.affiliation: Department of Chemical and Biomolecular Engineering, Vanderbilt University, 37235-1604, Nashville, TN, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Wan
authors.affiliation: Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, 310058, China. Electronic address: microbeapply@zju.edu.cn.
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002480:Cellulase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism; D006868:Hydrolysis; D008031:Lignin / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D014990:Xylans / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; D014990:Xylans; C095825:expansin protein, plant; C036909:lignocellulose; D002482:Cellulose; D008031:Lignin; D002480:Cellulase
keywords: BsEXLX1; Homologous modeling; Lignocellulose loosening; Site-directed mutagenesis; Synergistic activity