Issue 9, 2005

Strongly hydrogen-bonded water molecules in the Schiff base region of rhodopsins

Abstract

In many rhodopsins, a positively charged retinal chromophore is stabilized by a negatively charged carboxylate, and the presence of bound water molecules has been found in the Schiff base region by X-ray crystallography of various rhodopsins. Low-temperature Fourier-transform infrared (FTIR) spectroscopy can directly monitor hydrogen-bonding alterations of internal water molecules of rhodopsins. In particular, we found that a bridged water molecule between the Schiff base and Asp85 in bacteriorhodopsin (BR), a light-driven proton-pump protein, forms an extremely strong hydrogen bond. It is likely that a hydration switch of the water from Asp85 to Asp212 plays an important role in the proton transfer in the Schiff base region of BR. Comprehensive studies of archaeal and visual rhodopsins have revealed that strongly hydrogen-bonded water molecules are only found in the proteins exhibiting proton-pump activities. Strongly hydrogen-bonded water molecules and its transient weakening may be essential for the proton-pump function of rhodopsins.

Graphical abstract: Strongly hydrogen-bonded water molecules in the Schiff base region of rhodopsins

Article information

Article type
Perspective
Submitted
09 Nov 2004
Accepted
15 Feb 2005
First published
28 Feb 2005

Photochem. Photobiol. Sci., 2005,4, 661-666

Strongly hydrogen-bonded water molecules in the Schiff base region of rhodopsins

Y. Furutani, M. Shibata and H. Kandori, Photochem. Photobiol. Sci., 2005, 4, 661 DOI: 10.1039/B416698A

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