This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.106.101121v1 92/11/4045    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sasaki, J. Articles by Spudich, J. L. Search for Related Content PubMed PubMed Citation Articles by Sasaki, J. Articles by Spudich, J. L.

Different Dark Conformations Function in Color-Sensitive Photosignaling by the Sensory Rhodopsin I-HtrI Complex

Jun Sasaki ^*, Brian J. Phillips ^*, Xinpu Chen ^*, Ned Van Eps , Ah-Lim Tsai , Wayne L. Hubbell  and John L. Spudich ^*

^* Center for Membrane Biology, Department of Biochemistry & Molecular Biology, University of Texas Medical School, Houston, Texas 77030; Jules Stein Eye Institute, University of California School of Medicine, Los Angeles, California 90095; and Division of Hematology, Department of Internal Medicine, University of Texas Medical School, Houston, Texas 77030

Correspondence: Address reprint requests to John. L. Spudich, Center for Membrane Biology, Department of Biochemistry & Molecular Biology, University of Texas Medical School, Houston, TX 77030. E-mail: john.l.spudich{at}uth.tmc.edu.

The haloarchaeal phototaxis receptor sensory rhodopsin I (SRI) in complex with its transducer HtrI delivers an attractant signal from excitation with an orange photon and a repellent signal from a second near-UV photon excitation. Using a proteoliposome system with purified SRI in complex with its transducer HtrI, we identified by site-directed fluorescence labeling a site (Ser¹⁵⁵) on SRI that is conformationally active in signal relay to HtrI. Using site-directed spin labeling of Ser¹⁵⁵Cys with a nitroxide side chain, we detected a change in conformation following one-photon excitation such that the spin probe exhibits a splitting of the outer hyperfine extrema () significantly smaller than that of the electron paramagnetic resonance spectrum in the dark state. The dark conformations of five mutant complexes that do not discriminate between orange and near-UV excitation show shifts to lower or higher values correlated with the alterations in their motility behavior to one- and two-photon stimuli. These data are interpreted in terms of a model in which the dark complex is populated by two conformers in the wild type, one that inhibits the CheA kinase (A) and the other that activates it (R), shifted in the dark by mutations and shifted in the wild-type SRI-HtrI complex in opposite directions by one-photon and two-photon reactions.

This article has been cited by other articles:

				T. Kitajima-Ihara, Y. Furutani, D. Suzuki, K. Ihara, H. Kandori, M. Homma, and Y. Sudo Salinibacter Sensory Rhodopsin: SENSORY RHODOPSIN I-LIKE PROTEIN FROM A EUBACTERIUM J. Biol. Chem., August 29, 2008; 283(35): 23533 - 23541. [Abstract] [Full Text] [PDF]