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Dynamics of Water near a Protein Surface

Bhattacharyya, Sarika M. and Wang, Zhen-Gang and Zewail, Ahmed H. (2003) Dynamics of Water near a Protein Surface. Journal of Physical Chemistry B, 107 (47). pp. 13218-13228. ISSN 1520-6106. doi:10.1021/jp030943t.

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In this paper, we develop a model for the dynamics of water near a protein surface and compare with experimental results obtained with femtosecond resolution. The model consists of a layer of bound and free water molecules at the surface of the protein in dynamic equilibrium with each other, coupled to bulk water away from the protein surface. A previous model (Pal et al. J. Phys. Chem. B 2002, 106, 12376) considered the exchange in the layer without the coupling to the bulk. We find that water dynamics at the protein surface are described by two time scales, a fast, bulklike time scale, and a slower one more than 1 order of magnitude longer. The slow time scale, as in the previous model, is shown to be inversely proportional to the bound-to-free water conversion rate, k_2, but with a significant dependence on the free-to-bound conversion rate k_1, the diffusion of the free water molecules, and the thickness of the layer. This effect, identified as the feedback mechanism, is found to depend on the degree of orientation of the bound water molecules at the surface. The weight of the contribution of the slow component to the overall relaxation dynamics is shown to be inversely proportional to the slow decay time. For a heterogeneous surface with spatially varying k_2, the water dynamics in a probe region covering several sites is described by the cumulated effects from these water molecules, with the slow dynamics given by a sum of exponentials, with contributions inversely proportional to their respective decay times. To a very good degree, we find that this exponential behavior can be fitted to a single exponential; however, the apparent time scale does not represent that of any particular site. These conclusions are in good agreement with experimental results and provide important insight to the observed dynamical behavior.

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Wang, Zhen-Gang0000-0002-3361-6114
Additional Information:© 2003 American Chemical Society. Received: July 31, 2003. Publication Date (Web): November 1, 2003. This work was supported by the National Science Foundation. We thank Dr. Samir K. Pal for stimulating discussion and help. S.M.B. thanks Prof O. Bruno, Dr. A. Kamal, and A. Mukherjee for helpful discussions.
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Issue or Number:47
Record Number:CaltechAUTHORS:20160817-132622138
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Official Citation:Dynamics of Water near a Protein Surface Sarika M. Bhattacharyya, Zhen-Gang Wang, and Ahmed H. Zewail The Journal of Physical Chemistry B 2003 107 (47), 13218-13228 DOI: 10.1021/jp030943t
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69715
Deposited By: Ruth Sustaita
Deposited On:17 Aug 2016 21:39
Last Modified:11 Nov 2021 04:18

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