Freezing a Single Distal Motion in Dihidrofolate Reductase
| Autor: | Alessandro Sergi, Kim F. Wong, Sharon Hammes-Schiffer, James B. Watney |
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| Jazyk: | angličtina |
| Rok vydání: | 2006 |
| Předmět: |
Models
Molecular biology Chemistry Hydride Protein Conformation Coenzymes Motion (geometry) Biological Transport Catalysis Surfaces Coatings and Films Substrate Specificity Crystallography Molecular dynamics Kinetics Tetrahydrofolate Dehydrogenase Dihydrofolate reductase Freezing Materials Chemistry Biophysics biology.protein Quantum Theory Thermodynamics Physical and Theoretical Chemistry Quantum Free-Energy Perturbation Hydride Transfer Step Escherichia-Coli Molecular-Dynamics Electron-Transfer Catalytic Mechanism Hydrogen-Transfer Enzyme Catalysis Protein Dynamics Combined Quantum |
| Popis: | Constraining a single motion between distal residues separated by approximately 28 A in hybrid quantum/classical molecular dynamics simulations is found to increase the free energy barrier for hydride transfer in dihydrofolate reductase by approximately 3 kcal/mol. Our analysis indicates that a single distal constraint alters equilibrium motions throughout the enzyme on a wide range of time scales. This alteration of the conformational sampling of the entire system is sufficient to significantly increase the free energy barrier and decrease the rate of hydride transfer. Despite the changes in conformational sampling introduced by the constraint, the system assumes a similar transition state conformation with a donor-acceptor distance of approximately 2.72 A to enable the hydride transfer reaction. The modified thermal sampling leads to a substantial increase in the average donor-acceptor distance for the reactant state, however, thereby decreasing the probability of sampling the transition state conformations with the shorter distances required for hydride transfer. These simulations indicate that fast thermal fluctuations of the enzyme, substrate, and cofactor lead to conformational sampling of configurations that facilitate hydride transfer. The fast thermal motions are in equilibrium as the reaction progresses along the collective reaction coordinate, and the overall average equilibrium conformational changes occur on the slower time scale measured experimentally. Recent single molecule experiments suggest that at least some of these thermally averaged equilibrium conformational changes occur on the millisecond time scale of the hydride transfer reaction. Thus, introducing a constraint that modifies the conformational sampling of an enzyme could significantly impact its catalytic activity. |
| Databáze: | OpenAIRE |
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