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Ultrafast Protein Hydration Dynamics and Water-Protein Interactions

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2016, Doctor of Philosophy, Ohio State University, Physics.
Protein surface hydration is essential to its structure, dynamics and function. Understanding the nature of hydration dynamics and water-protein interactions has fundamental significance in protein science. In this dissertation, we employed state-of-the-art femtosecond laser spectroscopy and site-directed mutagenesis to study protein surface hydration with femtosecond temporal resolution and single-residue spatial resolution. With intrinsic optical probe of tryptophan, we have elucidated the relationship between hydration water and local protein fluctuations and also mapped the global water motions around two globular proteins, rat liver fatty acid-binding protein (rLFABP) and the B1 immunoglobin-binding domain of Streptococcal protein G (GB1). First, we investigated the ultrafast internal conversion dynamics between the two concurrently excited states of tryptophan (1La and 1Lb) in GB1 and clarified the internal conversion (40-80 fs) will not smear the ultrafast solvation dynamics probed by tryptophan and the slowdown of hydration dynamics observed in proteins is true. Then we studied the solvation dynamics of the single tryptophan in Staphylococcal nuclease (SNase) by systematically mutating its three neighboring charged residues to determine the contributions from hydration water and protein charged side chains. The results unambiguously show that the total Stokes shifts of tryptophan are dominantly from hydration water relaxations. The protein motions are restricted on the picosecond time scales and always slower than hydration dynamics. To unravel the mechanism of water-protein interactions, we examined the temperature dependence of interfacial water and protein side-chain relaxations simultaneously for SNase. Significantly, the observations suggest that the relaxations of protein side chains are intrinsically correlated to hydration dynamics with the same energy barriers and that hydration water motions dominate water-protein coupling and drive protein surface fluctuations on the sub-nanosecond time scale. Further, we characterized the global hydration dynamics around a ß-barrel protein rLFABP to examine the water-network flexibility around different protein secondary structures. The obtained results are compared with our previous studies on an a-helical globular protein apomyoglobin. Strikingly, we observed that the outer-layers hydration water is more retarded around ß-sheet structures and the water-protein restructuring dynamics around rLFABP surface is slower in comparison with apomyoglobin, revealing a potentially more extended hydration shell and a more rigid hydration water network around the ß-barrel protein. From numerous proteins we studied, two or three distinct hydration water relaxations were observed from sub-picosecond to hundreds of picoseconds. However, we observed four distinct relaxation time scales for GB1, a small domain protein with only 56 residues. The resulting solvation correlation functions can be expressed either by a four-phase exponential decay or a three-phase exponential decay integrated with a stretching exponent. The extraordinary solvation dynamics of GB1 indicate continuing hydration water relaxations coupled with protein motions at different time scales, including side-chain shaking, wobbling and even backbone fluctuations.
Dongping Zhong (Advisor)
David Stroud (Committee Member)
Ciriyam Jayaprakash (Committee Member)
Comert Kural (Committee Member)
163 p.

Recommended Citations

Citations

  • Yang, J. (2016). Ultrafast Protein Hydration Dynamics and Water-Protein Interactions [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480668103383892

    APA Style (7th edition)

  • Yang, Jin. Ultrafast Protein Hydration Dynamics and Water-Protein Interactions. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1480668103383892.

    MLA Style (8th edition)

  • Yang, Jin. "Ultrafast Protein Hydration Dynamics and Water-Protein Interactions." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480668103383892

    Chicago Manual of Style (17th edition)