Site-Specific Hydration Dynamics in the Nonpolar Core of a Molten Globule by Dynamic Nuclear Polarization of Water
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- 作者：Brandon D. Armstrong ; Jennifer Choi ; Carlos L贸pez ; Darryl A. Wesener ; Wayne Hubbell ; Silvia Cavagnero ; Songi Han
- 刊名：Journal of the American Chemical Society
- 出版年：2011
- 出版时间：April 20, 2011
- 年：2011
- 卷：133
- 期：15
- 页码：5987-5995
- 全文大小：924K
- 年卷期：v.133,no.15(April 20, 2011)
- ISSN：1520-5126
文摘
Water鈭抪rotein interactions play a direct role in protein folding. The chain collapse that accompanies protein folding involves extrusion of water from the nonpolar core. For many proteins, including apomyoglobin (apoMb), hydrophobic interactions drive an initial collapse to an intermediate state before folding to the final structure. However, the debate continues as to whether the core of the collapsed intermediate state is hydrated and, if so, what the dynamic nature of this water is. A key challenge is that protein hydration dynamics is significantly heterogeneous, yet suitable experimental techniques for measuring hydration dynamics with site-specificity are lacking. Here, we introduce Overhauser dynamic nuclear polarization at 0.35 T via site-specific nitroxide spin labels as a unique tool to probe internal and surface protein hydration dynamics with site-specific resolution in the molten globular, native, and unfolded protein states. The 1H NMR signal enhancement of water carries information about the local dynamics of the solvent within 10 脜 of a spin label. EPR is used synergistically to gain insights on local polarity and mobility of the spin-labeled protein. Several buried and solvent-exposed sites of apoMb are examined, each bearing a covalently bound nitroxide spin label. We find that the nonpoloar core of the apoMb molten globule is hydrated with water bearing significant translational dynamics, only 4鈭?-fold slower than that of bulk water. The hydration dynamics of the native state is heterogeneous, while the acid-unfolded state bears fast-diffusing hydration water. This study provides a high-resolution glimpse at the folding-dependent nature of protein hydration dynamics.