Scientists have revealed intricate atomic-scale structural changes in plants, fungi and bacteria in response to light in a new study.
The findings provide new insights into the function of protein molecules called phytochromes that are present in these three types of organisms. The results increase the understanding to control the function of phytochromes in plant cells, fungi or bacteria. The study was published in the open-access journal eLife in March 2020.
Plants constantly adapt to changes in light and control their growth accordingly. They achieve this through phytochromes, the origin of light detection in all vegetation on Earth. Phytochrome proteins can adopt two different shapes depending on the light available. To achieve this change in shape, a cascade of signals occurs starting at the chromophore – the point within the phytochrome where light is absorbed.
“The phytochrome allows organisms to distinguish between two colors of light, giving plants, fungi and bacteria a primitive two-color vision. Key to its function is the initial response to light, where the light signal is translated into structural changes over a fraction of a second”, explains lead author Elin Claesson, a doctoral student at the University of Gothenburg, Sweden.
“Studying such a fast light-induced mechanisms requires special technology that has only recently become available”, adds Heikki Takala, a postdoctoral researcher at the University of Jyväskylä and at the University of Helsinki Faculty of Medicine.
To address this opportunity, an international team that includes Prof. Janne Ihalainen, Dr. Heikki Takala and Prof. Gerrit Groenhoffrom the University of Jyväskylä, used a novel X-ray laser that can capture pictures of proteins at an atomic level every 10 femtoseconds (a quadrillionth of a second). This enabled them to reveal the movement of each atomic component of the phytochrome protein and helps to piece together the cascade of events that triggers growth in response to light.
Light causes reorganization in the protein
The team found surprisingly large rearrangements of the light-sensing chromophore and its surrounding protein structures immediately after light absorption. They observed the twisting of part of the chromophore called the D-ring, which in turn causes displacement of the neighboring rings as well as changes of atoms around the chromophore. Surprisingly, they also discovered the release of a water molecule, called pyrrole water, which is found in phytochromes across all organisms.
“These findings demonstrate that the initial response to light is highly collective and that many parts of the chromophore and phytochrome protein play an important role. We propose that these events work together enabling phytochrome proteins to translate light into structural signals, guiding the growth and development of plants, fungi and bacteria on Earth”, concludes senior author Sebastian Westenhoff.
”This breakthrough is a result of a long-standing collaboration where multidisciplinary expertise from protein science to laser spectroscopy and computational biomolecular chemistry is merged in a fruitful manner. The experimental approach with free-electron lasers is one of the few methods, if not the only one, which can be utilized for detecting such ultrafast atomic motions”, comments Janne Ihalainen, one of the senior scientist in the team.
The research has been made possible by funding from the Academy of Finland.
Header Image – The team found surprisingly large rearrangements of the light-sensing chromophore and its surrounding protein structures immediately after light absorption. CC BY 4.0 license.
