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Role of Rhodopsins as Circadian Photoreceptors in the Drosophila melanogaster
摘要： Light profoundly affects the circadian clock and the activity levels of animals. Along with the systematic changes in intensity and spectral composition, over the 24-h day, light shows considerable irregular fluctuations (noise). Using light as the Zeitgeber for the circadian clock is, therefore, a complex task and this might explain why animals utilize multiple photoreceptors to entrain their circadian clock. The fruit fly Drosophila melanogaster possesses light-sensitive Cryptochrome and seven Rhodopsins that all contribute to light detection. We review the role of Rhodopsins in circadian entrainment, and of direct light-effects on the activity, with a special emphasis on the newly discovered Rhodopsin 7 (Rh7). We present evidence that Rhodopsin 6 in receptor cells 8 of the compound eyes, as well as in the extra retinal Hofbauer-Buchner eyelets, plays a major role in entraining the fly’s circadian clock with an appropriate phase-to-light–dark cycles. We discuss recent contradictory findings regarding Rhodopsin 7 and report original data that support its role in the compound eyes and in the brain. While Rhodopsin 7 in the brain appears to have a minor role in entrainment, in the compound eyes it seems crucial for fine-tuning light sensitivity to prevent overshooting responses to bright light.
关键词： electroretinogram,Rhodopsins,entrainment,retina,Rhodopsin 7,immunocytochemistry
更新于2025-09-23 15:22:29
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Ancient Family of Retinal Proteins Brought to Light “Sight-Unseen”
摘要： Rhodopsins are an ancient class of light-sensing membrane proteins that bind retinylidene chromophores in order to form pigments that absorb visible light. Light absorption triggers isomerization of the chromophore, which is bound covalently within the transmembrane core of the protein, an event that drives protein conformational changes. Type-1 rhodopsins are also known as microbial rhodopsins, which include the well-known light-driven protein pump bacteriorhodopsin found in archeabacteria. Type-2 rhodopsins, or animal rhodopsins, include the sensory rhodopsins used as visual pigments found in most animals, including humans. Both Type-1 and -2 rhodopsins share a canonical seven-transmembrane helical polytopic structure with their amino terminal tails projecting to the topological outside of the cell membrane. Rhodopsins harness light energy to perform a vast array of functions, including pumping ions, gating channel activity, activating coupled enzyme systems, and transducing light sensation in vision. Pushkarev et al. have now reported the discovery of an entirely new group of microbial rhodopsins, opening up the potential for the elucidation of an extensive new class of rhodopsins that they term “heliorhodopsins.”
关键词： heliorhodopsins,retinylidene chromophores,light-sensing,membrane proteins,rhodopsins
更新于2025-09-23 15:21:21
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Strong pH-Dependent Near-Infrared Fluorescence in a Microbial Rhodopsin Reconstituted with a Red-Shifting Retinal Analogue
摘要： Near-infrared (NIR)-driven rhodopsins are of great interest in optogenetics and other optobiotechnological developments such as artificial photosynthesis and deep-tissue voltage imaging. Here we report the proton pump proteorhodopsin (PR) containing a NIR-active retinal analogue (PR:MMAR) exhibits intense NIR fluorescence at a quantum yield of 3.3%. This is 130 times higher than native PR (Lenz, M. O.; et al. Biophys J. 2006, 91, 255?262) and 3?8 times higher than the QuasAr and PROPS voltage sensors (Kralj, J.; et al. Science 2011, 333, 345?348; Hochbaum, D. R.; et al. Nat. Methods 2014, 11, 825?833). The NIR fluorescence strongly depends on the pH in the range of 6?8.5, suggesting potential application of MMAR-binding proteins as ultrasensitive NIR-driven pH and/or voltage sensors. Femtosecond transient absorption spectroscopy showed that upon near-IR excitation, PR:MMAR features an unusually long fluorescence lifetime of 310 ps and the absence of isomerized photoproducts, consistent with the high fluorescence quantum yield. Stimulated Raman analysis indicates that the NIR-absorbing species develops upon protonation of a conserved aspartate, which promotes charge delocalization and bond length leveling due to an additional methylamino group in MMAR, in essence providing a secondary protonated Schiff base. This results in much smaller bond length alteration along the conjugated backbone, thereby conferring significant single-bond character to the C13C14 bond and structural deformation of the chromophore, which interferes with photoinduced isomerization and extends the lifetime for fluorescence. Hence, our studies allow for a molecular understanding of the relation between absorption/emission wavelength, isomerization, and fluorescence in PR:MMAR. As acidification enhances the resonance state, this explains the strong pH dependence of the NIR emission.
关键词： stimulated Raman analysis,fluorescence,voltage sensor,rhodopsins,optogenetics,artificial photosynthesis,proteorhodopsin,femtosecond transient absorption spectroscopy,pH sensor,Near-infrared,voltage imaging
更新于2025-09-23 15:21:01
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Fluorescence enhancement of a microbial rhodopsin via electronic reprogramming
摘要： The engineering of microbial rhodopsins with enhanced fluorescence is of great importance in the expanding field of optogenetics. Here we report the discovery of two mutants (W76S/Y179F and L83Q) of a sensory rhodopsin from the cyanobacterium Anabaena PCC7120 with opposite fluorescence behavior. In fact, while W76S/Y179F displays, with respect to the wild-type protein, a nearly ten-fold increase in red-light emission, the second is not emissive. Thus, the W76S/Y179F, L83Q pair offers an unprecedented opportunity for the investigation of fluorescence enhancement in microbial rhodopsins, which is pursued by combining transient absorption spectroscopy and multi-configurational quantum chemistry. The results of such an investigation point to an isomerization-blocking electronic effect as the direct cause of instantaneous (sub-picosecond) fluorescence enhancement.
关键词： fluorescence enhancement,multi-configurational quantum chemistry,transient absorption spectroscopy,optogenetics,electronic reprogramming,microbial rhodopsins
更新于2025-09-04 15:30:14