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Analog Retinal Redshifts Visible Absorption of QuasAr Transmembrane Voltage Sensors into Near‐infrared
Author(s) -
Mei Gaoxiang,
Mamaeva Natalia,
Ganapathy Srividya,
Wang Peng,
DeGrip Willem J.,
Rothschild Kenneth J.
Publication year - 2019
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.13169
Subject(s) - chromophore , retinal , fluorescence , photochemistry , chemistry , materials science , optics , physics , biochemistry
Opsin‐based transmembrane voltage sensors (OTVSs) are increasingly important tools for neuroscience enabling neural function in complex brain circuits to be explored in live, behaving animals. However, the visible wavelengths required for fluorescence excitation of the current generation of OTVSs limit optogenetic imaging in the brain to depths of only a few mm due to the strong absorption and scattering of visible light by biological tissues. We report that substitution of the native A1 retinal chromophore of the widely used QuasAr1/2 OTVSs with the retinal analog MMAR containing a methylamino‐modified dimethylphenyl ring results in over a 100‐nm redshift of the maxima of the absorption and fluorescence emission bands to near 700 and 840 nm, respectively. FT‐Raman spectroscopy reveals that at pH 7 QuasAr1 with both the A1 and MMAR chromophores possess predominantly an all‐ trans protonated Schiff base configuration with the MMAR chromophore exhibiting increased torsion of the polyene single‐/double‐bond system similar to the O‐intermediate of the BR photocycle. In contrast, the A1 and the MMAR chromophores of QuasAr2 exist partially in a 13‐ cis PSB configuration. These results demonstrate that QuasArs containing the MMAR chromophore are attractive candidates for use as NIR‐OTVSs, especially for applications such as deep brain imaging.