MIPT researchers discovered how a protein that extends chromosomes plays a role in the response to oxidative stress.

Telomerase is an enzyme that extends the ends of chromosomes, enabling cells to bypass the limit on the number of divisions. However, the subunits of telomerase also perform other specific functions outside the cell nucleus. Researchers from Moscow Institute of Physics and Technology (MIPT), along with colleagues from the Institute of Bioorganic Chemistry (IBK RAS) and the Institute of Biochemical Physics (IBFM RAS) in Pushchino, have described the behavior of one of the polymerase components—TERT—under oxidative stress. It was found that this protein is transported to the mitochondria not from the nucleus, but is synthesized de novo by the cell.

2024-10-29 08:32:11https://naked-science.ru/article/column/otvete-na-okislitelnyj-st

The results have been published in the journal Scientific Reports. Mitochondria are organelles (literally "little organs") that tirelessly operate within human cells to facilitate respiration and provide energy for all metabolic processes. For this reason, they are often referred to as "cellular power plants."

The functioning of mitochondria resembles a hazardous production process, as they utilize oxygen and generate reactive oxygen species (ROS). These particles interact chaotically with other components, damaging various cell elements: they harm membranes, protein molecules, and can induce mutations. The result may be a range of diseases and accelerated aging.

Under normal conditions, the formation of ROS is balanced by antioxidant systems that neutralize them. However, this balance can be disrupted, leading to oxidative stress. Various protective mechanisms counteract this, including small antioxidant molecules (such as vitamins C and E) and specific enzymes. TERT (Telomerase Reverse Transcriptase) also plays a role in this stress response, being a component of the telomerase complex.

Its primary function is to protect the ends of chromosomes (telomeres) from "wearing down" during cell division. However, its subunits can also function independently, outside the nucleus. For instance, TERC (which is RNA) protects T-lymphocytes from programmed cell death, neurons from ROS damage, and is involved in inflammation. The new publication focuses on the TERT protein—the catalytic subunit of telomerase—which, in addition to lengthening chromosomes, is essential for regulating gene expression, RNA copying, and holds particular significance for mitochondria.

Biophysicists utilized "immortal" HeLa cells, originally obtained from a uterine tumor and cultured in laboratories since the mid-20th century. To induce oxidative stress in the cells, the researchers added hydrogen peroxide (H2O2) to the culture medium at a high concentration (500 mmol). It had previously been shown that excessive ROS increases TERT levels in mitochondria. However, it was unclear through which mechanism this occurred: whether through the transport of the protein into these organelles from the nucleus or its synthesis "on-site" within the mitochondria.

To address this question, the authors employed the SNAP-tag technology: adding a small "tag" protein to the target molecule, to which various markers can be attached. In this case, fluorescent dyes were used to track the localization of TERT within the cell. Popular fluorescent proteins like GFP are unsuitable for studying already mature proteins, as their structure does not allow them to penetrate these organelles.

“Proteins transported into mitochondria must pass through narrow membrane pores that are only 20 angstroms wide. This can occur either by 'unfolding' the protein with the help of special chaperone proteins and subsequently refolding it inside. Or through co-translational import, where the protein is synthesized by a ribosome 'sitting' directly on the mitochondrial membrane pore. We specifically investigated the import (direct transfer) of the TERT protein. It was necessary to determine how the molecule enters mitochondria under oxidative stress conditions. In the future, this will help us understand how the cell responds to such stress and what role TERT plays in this response,” explained the first author of the study, Dmitry Burkatovsky from the Center for Molecular Mechanisms of Aging and Age-Related Diseases at MIPT.

The researchers conducted a series of experiments using two approaches. Initially, they stained TERT in cells before adding hydrogen peroxide. Then, they used different dyes for staining—both before and after oxidative stress—which allowed them to track the localization of TERT and its potential movement. They were unable to detect the transport of the protein from the nucleus to the mitochondria. This suggests that mature TERT is likely formed within the organelles themselves, but the exact mechanism remains to be determined.