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J. Biol. Chem., Vol. 283, Issue 35, 23533-23541, August 29, 2008

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Salinibacter Sensory Rhodopsin

SENSORY RHODOPSIN I-LIKE PROTEIN FROM A EUBACTERIUM^*

Tomomi Kitajima-Ihara, Yuji Furutani, Daisuke Suzuki, Kunio Ihara^¶, Hideki Kandori, Michio Homma, and Yuki Sudo¹

From the Division of Biological Science, Graduate School of Science and the ^¶Center for Gene Research, Nagoya University, Chikusa-Ku, Nagoya, 464-8602, Japan and the Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya, 466-8555, Japan

Halobacterium salinarum sensory rhodopsin I (HsSRI), a dual receptor regulating both negative and positive phototaxis in haloarchaea, transmits light signals through changes in protein-protein interactions with its transducer, halobacterial transducer protein I (HtrI). Haloarchaea also have another sensor pigment, sensory rhodopsin II (SRII), which functions as a receptor regulating negative phototaxis. Compared with HsSRI, the signal relay mechanism of SRII is well characterized because SRII from Natronomonus pharaonis (NpSRII) is much more stable than HsSRI and HsSRII, especially in dilute salt solutions and is much more resistant to detergents. Two genes encoding SRI homologs were identified from the genome sequence of the eubacterium Salinibacter ruber. Those sequences are distantly related to HsSRI (40% identity) and contain most of the amino acid residues identified as necessary for its function. To determine whether those genes encode functional protein(s), we cloned and expressed them in Escherichia coli. One of them (SrSRI) was expressed well as a recombinant protein having all-trans retinal as a chromophore. UV-Vis, low-temperature UV-Vis, pH-titration, and flash photolysis experiments revealed that the photochemical properties of SrSRI are similar to those of HsSRI. In addition to the expression system, the high stability of SrSRI makes it possible to prepare large amounts of protein and enables studies of mutant proteins that will allow new approaches to investigate the photosignaling process of SRI-HtrI.

Received for publication, April 18, 2008 , and in revised form, June 5, 2008.

^* This work was supported by Grants 19042013 and 19045015 (to Y. F.), 19370067 and 20050015 (to H. K.), and 19870010 (to Y. S.) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 81-52-789-2993; Fax: 81-52-789-3001; E-mail: 4sudo{at}bunshi4.bio.nagoya-u.ac.jp.

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