MIPT biophysicists together with colleagues from Russia and Europe have determined the mechanism of proton transport through the cell membrane by photosensitive proteins. The results obtained will find application in the development of optogenetics, in the methodology of working with nerve cells. The results of the scientists' research are published in the journal Nature Structural & Molecular Biology.

Proton transport is extremely important for cell life: both bacterial and animal, as it plays a key role in energy exchange. It is carried out due to photosensitive rhodopsin proteins — they, like pumps, pump various ions through the cell membrane. Microbes have their own analogue of rhodopsins — bacteriorhodopsins. It is believed that the molecular mechanisms of proton movement through various types of proton-conducting molecules have common universal features. However, these mechanisms are still poorly understood. In their work, a team from the Center for Research on the Molecular Mechanisms of Aging and Age-Related Diseases of MIPT used xenorhodopsin from the bacterium Bacillus coahuilensis, discovered in Mexico.

"We studied xenorhodopsins in our work. This is a subgroup of microbial rhodopsins that pump a proton into the cell against the usual direction. They have been studied recently, since 2016. For the first time, our team studied their structure right in the process of their work using time-resolved crystallography. The protein is excited by a laser, and hundreds of microseconds later it is irradiated with X-rays. Thus, with the help of X—ray diffraction, we were able to obtain its structure," explained Fyodor Tsybrov, a researcher at the Center for Research on Molecular Mechanisms of Aging and Age—Related Diseases at MIPT.

The authors were able to identify the amino acids of xenorhodopsin BcXeR, which are involved in the proton transfer process. It turned out that the transfer process is carried out by "proton wires" — chains of hydrogen bonds formed between water molecules. These water molecules appear only in the process of protein work, so scientists saw them for the first time.

According to the authors, the results obtained will find application in optogenetics in the future. This is a technique for studying the work of nerve cells based on the introduction of special channels into their membrane — opsins that react to light excitation. If the brain is exposed to light with a certain wavelength, then those neurons that have such channels will be activated or vice versa: they will not be able to generate action potentials.

"Xenorhodopsins are an alternative to the current tool for stimulating cells with light. Based on the results obtained by us, it is possible to create new optogenetic tools. To do this, it is necessary to find such microbial rhodopsins that would work well in mammalian cells and would be safe when used in the body. Unfortunately, so far we have managed to achieve the functioning of our protein only in bacteria. For this purpose, new metagenomic data are analyzed, in which previously unexplored protein genes are found. Perhaps some of them will be suitable for optogenetics purposes. In particular, with the help of the current study, it will become clear how it can be modified and improved," Fyodor Tsybrov added.

In the future, the researchers also plan to accurately establish the biological role of xenorhodopsins in the bacterial cell — so far they cannot answer the question of why these proteins are needed by bacteria.

In addition to MIPT researchers, specialists from the University of Göttingen, the Institute of Biophysics of the Max Planck Society (Germany), the Institute of Structural Biology (France), the Joint Institute for Nuclear Research, Lomonosov Moscow State University and a number of other centers also took part in the study.

Source of information: MIPT press service

Photo source: © RIA Novosti / Vladimir Vyatkin

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