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Biophys. J. BioFAST: First Published November 12, 2004. doi:10.1529/biophysj.104.051490
© 2004 by the Biophysical Society.

A more recent version of this article appeared on February 1, 2005.
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CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING

Effect of Graded Hydration on the Dynamics of an Ion Channel Peptide: A Fluorescence Approach

Devaki A Kelkar 1 and Amitabha Chattopadhyay 2*

1 Centre for Cellular and Molecular Biology
2 Centre for Cellular & Molecular Biology

* To whom correspondence should be addressed. E-mail: amit{at}ccmb.res.in.

Submitted on August 17, 2004
Revised on September 18, 2004
Accepted on 4 November 2004


  Abstract
Water plays an important role in determining the folding, structure, dynamics, and in turn, the function of proteins. We have utilized a combination of fluorescence approaches such as the wavelength-selective fluorescence approach to monitor the effect of varying degrees of hydration on the organization and dynamics of the functionally important tryptophan residues of gramicidin in reverse micelles formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT). Our results show that tryptophans in gramicidin, present in the single stranded {beta}6.3 conformation, experience slow solvent relaxation giving rise to red edge excitation shift (REES). In addition, changes in fluorescence polarization with increasing excitation or emission wavelength reinforce that the gramicidin tryptophans are localized in motionally restricted regions of the reverse micelle. Interestingly, the extent of REES is found to be independent of the [water]/[surfactant] molar ratio (wo). We attribute this to heterogeneity in gramicidin tryptophan localization. Fluorescence intensity and mean fluorescence lifetime of the gramicidin tryptophans show significant reductions with increasing wo indicating sensitivity to increased polarity. Since the dynamics of hydration is related to folding, structure and eventually function of proteins, we conclude that REES could prove to be a potentially sensitive tool to explore the dynamics of proteins under conditions of changing hydration.

Key Words: Gramicidin, Hydration, Ion Channel, REES, Reverse Micelle




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Copyright © 2004 by the Biophysical Society.