Lórenz-Fonfría VA, Schultz BJ, Resler T, Schlesinger R, Bamann C, Bamberg E, Heberle J. Pre-gating conformational changes in the ChETA variant of channelrhodopsin-2 monitored by nanosecond IR spectroscopy.
J Am Chem Soc 2015;
137:1850-61. [PMID:
25584873 DOI:
10.1021/ja5108595]
[Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Light-gated ion permeation by channelrhodopsin-2 (ChR2) relies on the photoisomerization of the retinal chromophore and the subsequent photocycle, leading to the formation (on-gating) and decay (off-gating) of the conductive state. Here, we have analyzed the photocycle of a fast-cycling ChR2 variant (E123T mutation, also known as ChETA), by time-resolved UV/vis, step-scan FT-IR, and tunable quantum cascade laser IR spectroscopies with nanosecond resolution. Pre-gating conformational changes rise with a half-life of 200 ns, silent to UV/vis but detected by IR spectroscopy. They involve changes in the peptide backbone and in the H-bond of the side chain of the critical residue D156. Thus, the P1(500) intermediate must be separated into early and late states. Light-adapted ChR2 contains a mixture of all-trans and 13-cis retinal in a 70:30 ratio which are both photoactive. Analysis of ethylenic and fingerprint vibrations of retinal provides evidence that the 13-cis photocycle recovers in 1 ms. This recovery is faster than channel off-gating and most of the proton transfer reactions, implying that the 13-cis photocycle is of minor functional relevance for ChR2.
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