Title

Vibrational Frequency Shifts As A Probe Of Hydrogen Bonds: Thermal Expansion And Glass Transition Of Myoglobin In Mixed Solvents

Authors

Authors

F. Demmel; W. Doster; W. Petry;A. Schulte

Comments

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Abbreviated Journal Title

Eur. Biophys. J. Biophys. Lett.

Keywords

infrared spectroscopy; protein dynamics; amicle bands; preferential; hydration; INELASTIC NEUTRON-SCATTERING; RAMAN DIFFERENCE SPECTROSCOPY; PROTEIN; STRUCTURAL DYNAMICS; TEMPERATURE-DEPENDENCE; SUPERCOOLED WATER; MOSSBAUER-SPECTROSCOPY; HYDRATION; CRYSTALS; DISTRIBUTIONS; DIFFRACTION; Biophysics

Abstract

The contribution of hydrogen bonds to protein-solvent interactions and their impact on structural flexibility and dynamics of myoglobin are discussed. The shift of vibrational peak frequencies with the temperature of myoglobin in sucrose/water and glycerol/water solutions is used to probe the expansion of the hydrogen bond network. We observe a characteristic change in the temperature slope of the O-H stretching frequency at the glass transition which correlates with the discontinuity of the thermal expansion coefficient. The temperature-difference spectra of the amide bands show the same tendency, indicating that stronger hydrogen bonding in the bulk affects the main-chain solvent interactions in parallel. However, the hydrogen bond strength decreases relative to the bulk solvent with increasing cosolvent concentration near the protein surface, which suggests preferential hydration. Weaker and/or fewer hydrogen bonds are observed at low degrees of hydration. The central O-H stretching frequency of protein hydration water is red-shifted by 40 cm(-1) relative to the bulk. The shift increases towards lower temperatures, consistent with contraction and increasing strength of the protein-water bonds. The temperature slope shows a discontinuity near 180 K. The contraction of the network has reached a critical limit which leads to frozen-in structures. This effect may represent the molecular mechanism underlying the dynamic transition observed for the mean square displacements of the protein atoms and the heme iron of myoglobin.

Journal Title

European Biophysics Journal with Biophysics Letters

Volume

26

Issue/Number

4

Publication Date

1-1-1997

Document Type

Article

Language

English

First Page

327

Last Page

335

WOS Identifier

WOS:A1997XW99800006

ISSN

0175-7571

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