Steric constraint in the primary photoproduct of sensory rhodopsin II is a prerequisite for light-signal transfer to HtrII.
Sensory rhodopsin II (SRII, also called pharaonis phoborhodopsin, ppR) is responsible for negative phototaxis in Natronomonas pharaonis. Photoisomerization of the retinal chromophore from all- trans to 13- cis initiates conformational changes in the protein, leading to activation of the cognate transducer protein (HtrII). We previously observed enhancement of the C 14-D stretching vibration of the retinal chromophore at 2244 cm (-1) upon formation of the K state and interpreted that a steric constraint occurs at the C 14D group in SRII K. Here, we identify the counterpart of the C 14D group as Thr204, because the C 14-D stretching signal disappeared in T204A, T204S, and T204C mutants as well as a C 14-HOOP (hydrogen out-of-plane) vibration at 864 cm (-1). Although the K state of the wild-type bacteriorhodopsin (BR), a light-driven proton pump, possesses neither 2244 nor 864 cm (-1) bands, both signals appeared for the K state of a triple mutant of BR that functions as a light sensor (P200T/V210Y/A215T). We found a positive correlation between these vibrational amplitudes of the C 14 atom at 77 K and the physiological phototaxis response. These observations strongly suggest that the steric constraint between the C 14 group of retinal and Thr204 of the protein is a prerequisite for light-signal transduction by SRII.
Ito
Motohiro
M
Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
Sudo
Yuki
Y
Furutani
Yuji
Y
Okitsu
Takashi
T
Wada
Akimori
A
Homma
Michio
M
Spudich
John L
JL
Kandori
Hideki
H
D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002465:Cell Movement / Q000528:radiation effects; D006216:Halobacteriaceae / Q000502:physiology*; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D011485:Protein Binding; D015398:Signal Transduction; D017550:Spectroscopy, Fourier Transform Infrared; D013912:Threonine / Q000737:chemistry; D014961:X-Ray Diffraction
D019843:Archaeal Proteins; C100812:HtrII protein, Halobacterium salinarium; D013912:Threonine