The femtosecond-to-second photochemistry of red-shifted fast-closing anion channelrhodopsin PsACR1

Yusaku Hontani, Matthias Broser, Arita Silapetere, Benjamin S. Krause, Peter Hegemann, John T. M. Kennis

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Abstract

Anion channelrhodopsins (ACRs) are of great interest due to their ability to inhibit electrical signaling in optogenetic experiments. The photochemistry of ACRs is currently poorly understood and an improved understanding would be beneficial for rational design of ACRs with modified properties. Activation/deactivation of ACRs involves a series of photoreactions ranging from femtoseconds to seconds, thus real-time observation is essential to comprehend the full complexity of the photochemical processes. Here we investigate the photocycle of an ACR from Proteomonas sulcata (PsACR1), which is valuable for optogenetic applications due to the red-shifted absorption and action spectra compared to the prototype ACRs from Guillardia theta: GtACR1 and GtACR2, and the fast channel closing properties. From femto-to-submillisecond transient absorption spectroscopy, flash photolysis, and point mutations of acidic residues near the retinal Schiff base (RSB), E64, and D230, we found that the photoisomerization occurs in similar to 500 fs independent of the protonation state of E64. Notably, E64 is involved in the rearrangement of the hydrogen-bond network near the RSB after photoisomerization. Furthermore, we suggest that E64 works as a primary proton acceptor during deprotonation of the RSB as has been proposed for GtACR1. Our findings allow for a deeper understanding of the photochemistry on the activation/deactivation of ACRs.
Original languageEnglish
Pages (from-to)30402-30409
Number of pages8
JournalPhysical Chemistry Chemical Physics - PCCP
Volume19
Issue number45
Early online date24 Oct 2017
DOIs
Publication statusPublished - 7 Dec 2017

Funding

We thank Melanie Meiworm for technical assistance, and Shatanik Mukherjee for proofreading of the manuscript. Y. H. and J. T. M. K. were supported by the Chemical Sciences Council of the Netherlands Organization for Scientific Research (NWO) through a VICI grant to J. T. M. K. M. B., A. S., and P. H. were supported by the German Research foundation (SFB1078, B1). B. S. K. and P. H. are funded by the Cluster of Excellence 314 ‘‘Unifying Concepts in Catalysis’’ (Project E4/D4). P. H. is Hertie Senior Professor for Neuroscience and supported by the Hertie-Foundation. This work was supported by the Chemical Sciences Council of the Netherlands Organization for Scientific Research (NWO) through a Middelgroot investment grant to J. T. M. K.

FundersFunder number
Chemical Sciences Council
Hertie-Foundation
Netherlands Organization for Scientific Research
Deutsche ForschungsgemeinschaftE4/D4, SFB1078
Nederlandse Organisatie voor Wetenschappelijk Onderzoek

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