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.
