TY - JOUR
T1 - Effects of Chloride Ion Binding on the Photochemical Properties of Salinibacter Sensory Rhodopsin I
AU - Suzuki, Daisuke
AU - Furutani, Yuji
AU - Inoue, Keiichi
AU - Kikukawa, Takashi
AU - Sakai, Makoto
AU - Fujii, Masaaki
AU - Kandori, Hideki
AU - Homma, Michio
AU - Sudo, Yuki
N1 - Funding Information:
We thank Dr. Akira Kawanabe for assistance with the HPLC analysis and Dr. Tomomi Kitajima-Ihara and Ms. Akiko Okada for their encouragement. The present work was financially supported in part by a Grant-in-Aid for Scientific Research (KAKENHI) on Priority Area (Area No. 477) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. This work was also supported by grants from the Japanese Ministry of Education, Culture, Sports, Science, and Technology to Y.F, (19042013 and 19045015), to H.K. (19370067 and 20050015), and to Y.S. (20050012).
PY - 2009/9/11
Y1 - 2009/9/11
N2 - Microbial organisms utilize light not only as energy sources but also as signals by which rhodopsins (containing retinal as a chromophore) work as photoreceptors. Sensory rhodopsin I (SRI) is a dual photoreceptor that regulates both negative and positive phototaxis in microbial organisms, such as the archaeon Halobacterium salinarum and the eubacterium Salinibacter ruber. These organisms live in highly halophilic environments, suggesting the possibility of the effects of salts on the function of SRI. However, such effects remain unclear because SRI proteins from H. salinarum (HsSRI) are unstable in dilute salt solutions. Recently, we characterized a new SRI protein (SrSRI) that is stable even in the absence of salts, thus allowing us to investigate the effects of salts on the photochemical properties of SRI. In this study, we report that the absorption maximum of SrSRI is shifted from 542 to 556 nm in a Cl--dependent manner with a Km of 307 ± 56 mM, showing that Cl--binding sites exist in SRI. The bathochromic shift was caused not only by NaCl but also by other salts (NaI, NaBr, and NaNO3), implying that I-, Br-, and NO3- can also bind to SrSRI. In addition, the photochemical properties during the photocycle are also affected by chloride ion binding. Mutagenesis studies strongly suggested that a conserved residue, His131, is involved in the Cl--binding site. In light of these results, we discuss the effects of the Cl- binding to SRI and the roles of Cl- binding in its function.
AB - Microbial organisms utilize light not only as energy sources but also as signals by which rhodopsins (containing retinal as a chromophore) work as photoreceptors. Sensory rhodopsin I (SRI) is a dual photoreceptor that regulates both negative and positive phototaxis in microbial organisms, such as the archaeon Halobacterium salinarum and the eubacterium Salinibacter ruber. These organisms live in highly halophilic environments, suggesting the possibility of the effects of salts on the function of SRI. However, such effects remain unclear because SRI proteins from H. salinarum (HsSRI) are unstable in dilute salt solutions. Recently, we characterized a new SRI protein (SrSRI) that is stable even in the absence of salts, thus allowing us to investigate the effects of salts on the photochemical properties of SRI. In this study, we report that the absorption maximum of SrSRI is shifted from 542 to 556 nm in a Cl--dependent manner with a Km of 307 ± 56 mM, showing that Cl--binding sites exist in SRI. The bathochromic shift was caused not only by NaCl but also by other salts (NaI, NaBr, and NaNO3), implying that I-, Br-, and NO3- can also bind to SrSRI. In addition, the photochemical properties during the photocycle are also affected by chloride ion binding. Mutagenesis studies strongly suggested that a conserved residue, His131, is involved in the Cl--binding site. In light of these results, we discuss the effects of the Cl- binding to SRI and the roles of Cl- binding in its function.
KW - anion binding
KW - color tuning
KW - phototaxis
KW - sensory rhodopsin
KW - signal transduction
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U2 - 10.1016/j.jmb.2009.06.050
DO - 10.1016/j.jmb.2009.06.050
M3 - Article
C2 - 19560470
AN - SCOPUS:68949186439
VL - 392
SP - 48
EP - 62
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
SN - 0022-2836
IS - 1
ER -