During evolution, LOV proteins may have arisen from flavin-binding precursors that lacked both the glutamine and a cysteine residue. Later acquisition of both residues would have rendered signal transduction upon blue light absorption more efficient. (c) Andreas Möglich.
Crystal structures of a LOV protein with the glutamine replaced by a leucine (L513). Compared to the dark state (left), the LOV protein exhibits rearrangements of certain residues, e.g., asparagine N414, upon blue light absorption. (c) Andreas Möglich.
Several types of blue light-absorbing photoreceptors occur in nature. Especially well-represented are light-oxygen-voltage proteins, or LOV proteins for short. Light triggers chemical reactions inside LOV receptors that enable plants, fungi and bacteria to respond to sunlight for their own benefit. For example, plant growth is oriented to the direction of incident light – a phenomenon known as phototropism. At the same time, photoreceptors serve as important building blocks in optogenetics. Absorbed blue light can be harnessed for the regulation of cellular processes, including the expression of genes and the structure and dynamics of the cytoskeleton.
It has been long known that blue light triggers photochemical reactions in LOV proteins that lead to the transfer of hydrogen atoms. In this way, protonation changes take place, as confirmed back in 2015 by a Bayreuth research team led by Prof. Dr. Andreas Möglich. A specific glutamine plays the role of recognizing these processes and sending corresponding signals into the cells. The new study now focuses on the role of this very glutamine. With but few exceptions, this glutamine is present in almost all LOV proteins, indicating its central importance.
"Contrary to the established view in research, our experiments showed that the reactions set in motion by blue light absorption do not necessarily rely on glutamine. The photochemical systems in numerous plants, fungi, and bacteria are structured in such a way to allow these molecular processes, in principle, to take place even if the photoreceptors did not contain glutamine. They then only proceed more slowly and less efficiently," says Prof. Dr. Andreas Möglich, Professor of Photobiochemistry at the University of Bayreuth and corresponding author of the study. As studies of high-resolution images of LOV protein crystal structures and simulations of molecular processes have shown, it does not have to be glutamine that informs the cells about the protonation changes triggered by blue light. This task can equally be performed by water molecules that penetrate the LOV proteins after light absorption.
"Our research results provide new insights into the mechanism of blue light absorption performed by LOV proteins and into the signal transduction it triggers. At the same time, we have found revealing clues that may help us solve a still completely unsolved mystery, namely, the question of how blue light receptors evolved in the course of evolution. There is much to suggest that they evolved from metabolic enzymes capable of binding yellow pigments known as flavins. Moreover, our study has implications for future investigations of processes regulated by photoreceptors. Unlike in the past, the lack of glutamine in itself can no longer be regarded as a sufficient condition for abrogating signal transduction," says Möglich.
The Bayreuth biochemist also points out the importance of the new findings for biotechnological research involving photoreceptors. LOV proteins are mainly used for this purpose. For example, modified LOV proteins are used to generate reactive species of oxygen after the removal of glutamine and other molecular units. These are particularly reactive forms of oxygen that cause chemical reactions and promote aging processes and various diseases.
The findings, published in Nature Communications, are the result of collaboration between the Bayreuth research group of Prof. Dr. Andreas Möglich and partners at the University of Bonn and the Hebrew University in Jerusalem. The three first authors, Julia Dietler, Renate Gelfert, and Jennifer Kaiser, all received their doctorates in biochemistry from the University of Bayreuth. They now work in renowned international companies and research centres.
Contact for scientific information:
Prof. Dr. Andreas Möglich
Photobiochemistry
University of Bayreuth
Phone: +49 (0)921 / 55-7835
E-mail: andreas.moeglich@uni-bayreuth.de
Original publication:
Julia Dietler et al.: Signal transduction in light-oxygen-voltage receptors lacking the active-site glutamine. Nature Communications 2022, DOI: 10.1038/ncomms10079 10.1038/s41467-022-30252-4 // https://www.nature.com/articles/s41467-022-30252-4
See also the above mentioned earlier study:
Estella F. Yee et al.: Signal transduction in light-oxygen-voltage receptors lacking the adduct-forming cysteine residue. Nature Communications (2015), DOI: 10.1038/ncomms10079 // https://www.nature.com/articles/ncomms10079
