title: Internal water molecules of the proton-pumping halorhodopsin in the presence of azide.
abstract: In the FTIR study of rhodopsins, we have so far found that strongly hydrogen-bonded water molecules (O-D stretch at <2400 cm-1) are only present in the proteins exhibiting proton-pumping activity. Halorhodopsin (HR) is a light-driven chloride pump in haloarchaea, which does not possess such water molecules. On the other hand, it is known that addition of azide converts HR into a proton pump. Although the mechanism has not been understood, we observed strongly hydrogen-bonded water molecules in the azide-bound HR of Natronobacterium pharaonis (pHR). This finding is consistent with the previous results, implying that the presence of strongly hydrogen-bonded water molecules is requested for the proton-pumping function of rhodopsins.
authors: Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
authors: Norikazu
authors: N
authors: Muneda
authors: Mikihiro
authors: M
authors: Shibata
authors: Makoto
authors: M
authors: Demura
authors: Hideki
authors: H
authors: Kandori