title: Structures of a glucose-tolerant β-glucosidase provide insights into its mechanism.
abstract: Cellulose can be converted to ethanol via the fermentation of glucose, which is considered as a promising green alternative for transportation fuels. The conversion of cellulose to glucose needs three enzymes, in which β-glucosidase (BGL) plays an essential role. However, BGL is inhibited by its own product glucose, greatly limiting its applications in industry. We previously obtained a novel BGL named Bgl6 with a high glucose tolerance. Further engineering through random mutagenesis produced a triple mutant M3 with improved thermostability. This enzyme shows promising properties for wide applications but the structural basis of the unusual properties of Bgl6 is not clear. In this study, we determined the crystal structures of Bgl6 and variants at high resolution, which provide insights into its glucose-tolerant mechanism and thermostability. Particularly, Bgl6 forms an extra channel that could be used as a secondary binding site for glucose, which may contribute to glucose tolerance. Additionally, the triple mutations could strengthen the hydrophobic interactions within the enzyme and may be responsible for the enhanced thermostability exhibited by M3, which was further confirmed by dynamic light scattering data. Lastly, structural comparison to other orthologs allows us to formulate new strategies on how to improve the catalytic efficiency of Bgl6.
authors.affiliation: School of Pharmaceutical Sciences, The Sun Yat-Sen University, 132 E. Circle Rd. University City, Guangzhou, Guangdong 510006, People's Republic of China; Center for Cellular & Structural Biology, The Sun Yat-Sen University, 132 E. Circle Rd., University City, Guangzhou, Guangdong 510006, People's Republic of China.
authors.forename: Panjiao
authors.initials: P
authors.lastname: Pang
authors.affiliation: School of Life Sciences, The Sun Yat-Sen University, 135 W. Xingang Rd., Guangzhou, Guangdong 510275, People's Republic of China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Sun Yat-sen University, 135 W. Xingang Rd., Guangzhou 510275, People's Republic of China.
authors.forename: Li-Chuang
authors.initials: LC
authors.lastname: Cao
authors.affiliation: School of Life Sciences, The Sun Yat-Sen University, 135 W. Xingang Rd., Guangzhou, Guangdong 510275, People's Republic of China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Sun Yat-sen University, 135 W. Xingang Rd., Guangzhou 510275, People's Republic of China.
authors.forename: Yu-Huan
authors.initials: YH
authors.lastname: Liu
authors.affiliation: Center for Cellular & Structural Biology, The Sun Yat-Sen University, 132 E. Circle Rd., University City, Guangzhou, Guangdong 510006, People's Republic of China; School of Life Sciences, The Sun Yat-Sen University, 135 W. Xingang Rd., Guangzhou, Guangdong 510275, People's Republic of China. Electronic address: xiewei6@mail.sysu.edu.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Xie
authors.affiliation: School of Pharmaceutical Sciences, The Sun Yat-Sen University, 132 E. Circle Rd. University City, Guangzhou, Guangdong 510006, People's Republic of China; Center for Cellular & Structural Biology, The Sun Yat-Sen University, 132 E. Circle Rd., University City, Guangzhou, Guangdong 510006, People's Republic of China. Electronic address: wangzh357@mail.sysu.edu.cn.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Wang
mesh_terms: D001426:Bacterial Proteins; D001665:Binding Sites; D002482:Cellulose / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D005947:Glucose / Q000737:chemistry*; D015394:Molecular Structure; D009154:Mutation; D015202:Protein Engineering; D055550:Protein Stability; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D002482:Cellulose; D001617:beta-Glucosidase; D005947:Glucose
keywords: Catalysis; Crystal structure; Glucose-tolerant; Thermostability; β-Glycosidase