Five residues in the HtrI transducer membrane-proximal domain close the cytoplasmic proton-conducting channel of sensory rhodopsin I.

The Journal of Biological Chemistry
Xinpu Chen, J L Spudich

Abstract

Transducer-free sensory rhodopsins carry out light-driven proton transport in Halobacterium salinarum membranes. Transducer binding converts the proton pumps to signal-relay devices in which the transport is inhibited. In sensory rhodopsin I (SRI) binding of its cognate transducer HtrI inhibits transport by closing a cytoplasmic proton-conducting channel necessary for proton uptake during the SRI photochemical reaction cycle. To investigate the channel closure, a series of HtrI mutants truncated in the membrane-proximal cytoplasmic portion of an SRI-HtrI fusion were constructed and expressed in H. salinarum membranes. We found that binding of the membrane-embedded portion of HtrI is insufficient for channel closure, whereas cytoplasmic extension of the second HtrI transmembrane helix by 13 residues blocks proton conduction through the channel as well as full-length HtrI. Specifically the closure activity is localized in this 13-residue membrane-proximal cytoplasmic domain to the 5 final residues, each of which incrementally contributes to reduction of proton conductivity. Moreover, these same residues in the dark incrementally and proportionally increase the pKa of the Asp-76 counterion to the protonated Schiff base chromophore...Continue Reading

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Citations

Aug 31, 2010·Journal of Bacteriology·Hsu-Yuan FuChii-Shen Yang
Oct 20, 2006·Proceedings of the National Academy of Sciences of the United States of America·Yuki Sudo, John L Spudich
Mar 12, 2013·Journal of Photochemistry and Photobiology. B, Biology·Hsu-Yuan FuChii-Shen Yang
Sep 15, 2005·The Journal of Biological Chemistry·Enrica BordignonHeinz-Jürgen Steinhoff

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