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Updated: Jun 20, 2026

Strategic Screening and Characterization of the Visual GPCR-mini-G Protein Signaling Complex for Successful Crystallization
Published on: March 16, 2020
Characterization of a signaling complex composed of sensory rhodopsin I and its cognate transducer protein from the
Yuki Sudo1, Akiko Okada, Daisuke Suzuki
1Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. z47867a@cc.nagoya-u.ac.jp
Abstract:
Sensory rhodopsin I (SRI) exists in the cell membranes of microorganisms such as the archaeon Halobacterium salinarum and is a photosensor responsible for positive and negative phototaxis. SRI forms a signaling complex with its cognate transducer protein, HtrI, in the membrane. That complex transmits light signals to the flagellar motor through changes in protein-protein interactions with the kinase CheA and the adaptor protein CheW, which controls the direction of the rotation of the flagellar motor. Recently, we cloned and characterized Salinibacter sensory rhodopsin I (SrSRI), which is the first SRI-like protein identified in eubacteria [Kitajima-Ihara, T., et al. (2008) J. Biol. Chem. 283, 23533-23541]. Here we cloned and expressed SrSRI with its full-length transducer protein, SrHtrI, as a fusion construct. We succeeded in producing the complex in Escherichia coli as a recombinant protein with high quality having all-trans-retinal as a chromophore for SRI, although the expression level was low (0.10 mg/L of culture). In addition, we report here the photochemical properties of the SrSRI-SrHtrI complex using time-resolved laser flash spectroscopy and other spectroscopic techniques and compare them to SrSRI without SrHtrI.
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