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KMID : 1161520050090030139
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Animal Cells and Systems
2005 Volume.9 No. 3 p.139 ~ p.144
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Glu-56 in HtrI is critical for phototaxis signaling in halobacterium salinarum
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Choi Ah-Reum
Kim So-Young
Yoon Sa-Ryong
Jung Kwang-Hwan
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Abstract
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The attractant (orange light) or repellent (white light) signal is transmitted from SRI (Sensory Rhodopsin I) via protein?protein interaction with its transducer HtrI (Halobacterial Transducer for Sensory Rhodopsin I) which in turn controls a cytoplasmic phospho?transfer pathway that modulates flagella motor switching in Halobacterium salinarum. Some mutations in both SRI and HtrI showed an unusual mutant phenotype called inverted signaling, in which the cell produces a repellent response to normally attractant light. Twelve mutations at the Glutamate 56 (E56) position in the second transmembrane helix of HtrI were introduced by site?specific random mutagenesis. Almost all E56 mutants showed orange?light inverted responses in pH and temperature?dependent manners except E56D and E56Y. Except for these two mutants, all mutants accelerated the S373 decay compared to wild?type at 18°C. This supported that there is an interaction between SRI and the second transmembrane of HtrI. Also a structural model of HtrI based on the Tar crystal structure and the secondary structure prediction program proposed the E56 residue to be in the middle of the proton channel. The most important observation is that the E56 mutant provides the evidence that this residue is very sensitive for signal relay, which can be explained by the open and closed conformations of the channel (A and R conformations) in SRI, as was postulated by the unified conformational shuttling model for transport and signaling.
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KEYWORD
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Sensory rhodopsin, retinal, photoreceptor, signal transduction, inverted response
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