Using various spectroscopic methods, researchers at Ruhr-Universität Bochum (RUB) and Philipps-Universität Marburg have gained new insights into how the light-sensitive part of the biomolecule phytochrome changes from a light-adapted to a dark-adapted state. They found that cyanobacterial and plant phytochromes could transduce red and far-red light stimulus into a mechanical output. Their discovery could be put to potential use as an optogenetic tool. Phytochromes from plants react to red and infrared light. Courtesy of RUB, Kramer. The researchers analyzed a phytochrome molecule from cyanobacteria using a special form of mass spectrometry and electron spin resonance spectrometry. Through the use of these methods, they were able to study the molecule in solution and track its structural changes without having to crystallize it. They observed several characteristic structural changes in the light-sensitive segment of the phytochrome and created a model that showed the light-triggered conversion steps. In addition, the team showed that for different phytochromes, there is a universal mechanism for the transformation from the dark-adapted to the light-adapted state. At present, the structures of just a few light-sensitive biomolecules are known, and understanding of their structures extends only to their final states in light and darkness, not to the intermediate states. The Bochum-based research team: Enrica Bordignon and Tufa Assafa. Courtesy of RUB, Kramer. “So far, however, it has been a challenge to decipher these processes with atomic resolution,” said researcher Tufa Assafa, who investigated dynamic structural changes in the light-sensitive biomolecules. A better understanding of how the photoreceptors in the biomolecules change their spatial structure when exposed to light could advance applications in biophotonics and other areas. “Light-sensitive biomolecules such as phytochromes from plants are interesting for various applications, for example in agriculture, where a change in phytochrome could optimize the growth habits of plants, or for optogenetic tools that make it possible to control the activity of genetically modified cells in the living body with light,” said Enrica Bordignon, head of Bochum’s EPR Spectroscopy Working Group. The research was published in Structure (http://dx.doi.org/10.1016/j.str.2018.08.003).