Table of Contents
Journal of Biophysics
Volume 2008, Article ID 267912, 11 pages
Research Article

Flexibility of the Cytoplasmic Domain of the Phototaxis Transducer II from Natronomonas pharaonis

1Institute for Structural Biology (IBI-2), Research Center Jülich, 52425 Jülich, Germany
2Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA

Received 29 May 2008; Accepted 21 July 2008

Academic Editor: Thomas P. Burghardt

Copyright © 2008 Ivan L. Budyak et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Chemo- and phototaxis systems in bacteria and archaea serve as models for more complex signal transduction mechanisms in higher eukaryotes. Previous studies of the cytoplasmic fragment of the phototaxis transducer (pHtrII-cyt) from the halophilic archaeon Natronomonas pharaonis showed that it takes the shape of a monomeric or dimeric rod under low or high salt conditions, respectively. CD spectra revealed only approximately 24% helical structure, even in 4 M KCl, leaving it an open question how the rod-like shape is achieved. Here, we conducted CD, FTIR, and NMR spectroscopic studies under different conditions to address this question. We provide evidence that pHtrII-cyt is highly dynamic with strong helical propensity, which allows it to change from monomeric to dimeric helical coiled-coil states without undergoing dramatic shape changes. A statistical analysis of predicted disorder for homologous sequences suggests that structural flexibility is evolutionarily conserved within the methyl-accepting chemotaxis protein family.