Far-Red Absorbing Rhodopsins, Insights From Heterodimeric Rhodopsin-Cyclases

The recently discovered Rhodopsin-cyclases from Chytridiomycota fungi show completely unexpected properties for microbial rhodopsins. These photoreceptors function exclusively as heterodimers, with the two subunits that have very different retinal chromophores. Among them is the bimodal photoswitchable Neorhodopsin (NeoR), which exhibits a near-infrared absorbing, highly fluorescent state. These are features that have never been described for any retinal photoreceptor. Here these properties are discussed in the context of color-tuning approaches of retinal chromophores, which have been extensively studied since the discovery of the first microbial rhodopsin, bacteriorhodopsin, in 1971 (Oesterhelt et al., Nature New Biology, 1971, 233 (39), 149-152). Further a brief review about the concept of heterodimerization is given, which is widely present in class III cyclases but is unknown for rhodopsins. NIR-sensitive retinal chromophores have greatly expanded our understanding of the spectral range of natural retinal photoreceptors and provide a novel perspective for the development of optogenetic tools.

Automated summary

The recently discovered Rhodopsin-cyclases from Chytridiomycota fungi exhibit unexpected properties, functioning exclusively as heterodimers with distinct retinal chromophores. The bimodal photoswitchable Neorhodopsin is particularly noteworthy for its near-infrared absorption and high fluorescence, which have not been observed in other retinal photoreceptors. This article discusses these properties in the context of retinal chromophore color-tuning approaches and provides a brief review of heterodimerization, shedding light on the development of optogenetic tools.