Title

Vibrational frequency shifts as a probe of hydrogen bonds: Thermal expansion and glass transition of myoglobin in mixed solvents

Keywords

Amicle bands; Infrared spectroscopy; Preferential hydration; Protein dynamics

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.

Publication Date

10-3-1997

Publication Title

European Biophysics Journal

Volume

26

Issue

4

Number of Pages

327-335

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1007/s002490050087

Socpus ID

0030771840 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/0030771840

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