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The Coupled Water-Protein Dynamics within Hydration Layer surrounding Protein and Semiclassical Approximation for Optical Response Funtion

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2011, Doctor of Philosophy, Ohio State University, Biophysics.

We report experimental and theoretical studies on water and protein dynamics following photoexcitation of apomyoglobin. Using site-directed mutation and with femtosecond resolution, we experimentally observed relaxation dynamics with a biphasic distribution of time scales, 5 and 87 ps, around the site Trp7. Theoretical studies using both linear response and direct nonequilibrium molecular dynamics (MD) calculations reproduced the biphasic behavior. Further constrained MD simulations with either frozen protein or frozen water revealed the molecular mechanism of slow hydration processes and elucidated the role of protein fluctuations. Observation of slow water dynamics in MD simulations requires protein flexibility, regardless of whether the slow Stokes shift component results from the water or protein contribution. The initial dynamics in a few picoseconds represents fast local motions such as reorientations and translations of hydrating water molecules, followed by slow relaxation involving strongly coupled water-protein motions. We observed a transition from one isomeric protein configuration to another after 10 ns during our 30 ns ground-state simulation. For one isomer, the surface hydration energy dominates the slow component of the total relaxation energy. For the other isomer, the slow component is dominated by protein interactions with the chromophore. In both cases, coupled water-protein motion is shown to be necessary for observation of the slow dynamics. Such biologically important water-protein motions occur on tens of picoseconds. One significant discrepancy exists between theory and experiment, the large inertial relaxation predicted by simulations but clearly absent in experiment. Further improvements required in the theoretical model are discussed.

Linear response theory has been reported to give good approximations with the nonequilibrium relaxation of Stokes shift in the studies of solvation dynamics. It breaks down for Trp-140 (W140) in Staphylococcus nuclease. Two isomers are found in the electronic ground state of Trp on the time scale of 35 nanosecond simulation. Isomerization of local structure around W151 is crucial to explain the mechanism how linear response theory deviates from the nonequilibrium process.

Dongping Zhong (Committee Chair)
Sherwin Singer (Advisor)
Chenglong Li (Committee Member)
131 p.

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Citations

  • Li, T. (2011). The Coupled Water-Protein Dynamics within Hydration Layer surrounding Protein and Semiclassical Approximation for Optical Response Funtion [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1312484867

    APA Style (7th edition)

  • Li, Tanping. The Coupled Water-Protein Dynamics within Hydration Layer surrounding Protein and Semiclassical Approximation for Optical Response Funtion. 2011. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1312484867.

    MLA Style (8th edition)

  • Li, Tanping. "The Coupled Water-Protein Dynamics within Hydration Layer surrounding Protein and Semiclassical Approximation for Optical Response Funtion." Doctoral dissertation, Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1312484867

    Chicago Manual of Style (17th edition)