Discovery of “Heliorhodopsin”, a novel type of photo-receptive membrane protein A new light utilization strategy of living organisms
A research group discovered a novel type of photo-receptive membrane protein, rhodopsin, and it was named “Heliorhodopsin”. This research was achieved by the international collaborative group of Professor Hideki Kandori, Associate Professor Keiichi Inoue (Present at the Institute for Solid State Physics, the University of Tokyo), Research Associate Professor Satoshi P. Tsunoda at OptoBio Technology Research Center, Nagoya Institute of Technology, and Professor Oded Béjà at Technion Israel Institute of Technology, Israel.
The research revealed that the amino-acid sequence of this new rhodopsin is highly different from that of type-1 and type-2 rhodopsins which were derived from micro-organisms and animals, respectively. Despite of this large differences of the sequence, it was found that heliorhodopsin binds the same type of retinal molecule as type-1 rhodopsin and shows similar photoreaction process involving retinal-isomerization and proton transfer reaction upon light illumination (Figure).
The discovery of heliorhodopsin proved the presence of a new photobiological strategy using sun-light by the living organisms on the Earth and it is expected to lead developments of new optogenetics in the future.
The research paper was published in the Nature online (June 20, 2018).
Figure. The photo-reaction cycle of heliorhodopsin
Heliorhodopsin shows photo-isomerization of retinal molecule and proton transfer reaction upon light illumination. Despite of large difference in amino-acid sequence, it shows a photo-reaction cycle involving K, M and O intermediate, similar to that of type-1 rhodopsin. On the other hand, the detailed biophysical analysis revealed the distinct molecular aspects of heliorhodopsin that differ from type-1.