Conformational modeling of substrate binding to endocellulase E2 from Thermomonospora fusca |
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Authors: | Taylor JS; Teo B; Wilson DB |
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Affiliation: | Department of Food Science Stocking Hall, Cornell University, Ithaca, NY 14853, USA
1Department of Biochemistry, Cornell University, Ithaca, NY 14853, USA |
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Abstract: | Molecular mechanics calculations have been used to place a cellotetraosesubstrate into the active site of the crystallographlcally determinedstructure of endocellulase E2 from Thermomonospora fusca. Inthe lowest energy model structure, the second residue of thesubstrate oligosaccharide is tilted away from the planar ribbongeometry of cellulose as it is in the Xray structureof the E2cdcellobiose cocrystal. This tilt is the resultof the topology of the binding site, and results in severalstrong carbohydrateprotein hydrogen bonds. The tiltingproduces a twisting of the glycosidic linkage of the cleavagesite between residues two and three. In the predicted enzymesubstratecomplex both of the Asp residues believed to function in generalacid and base roles in the previously proposed model for themechanism are distant from the bond being cleaved. Moleculardynamics simulations of the complex were conducted, and whilethe putative catalytic Asp residues remained distant from thecleavage site, the proton of Tyr73 briefly came within van derWaals contact of the linkage oxygen. |
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Keywords: | cellulases/ computer modeling/ enzymatic mechanisms/ substrate binding |
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