NEDDylation stabilizes eIF3g and eIF3i during stress

Inside every living cell, a constant, delicate machinery works to turn genetic instructions into the proteins that build and repair the body. This process, known as translation, relies on a team of molecular helpers that gather at the start of a genetic message to begin construction. However, when a cell faces sudden trouble, such as a toxic chemical or extreme heat, it must hit the pause button. To survive, the cell forms temporary, gel-like clusters in its fluid interior called stress granules. These structures act as holding pens, locking away the stalled construction teams and their unfinished blueprints until the danger passes. Once the environment stabilizes, the cell needs to quickly release these teams to resume building. A critical question for scientists has been how specific parts of the construction team are selected to enter these holding pens and, just as importantly, how they are protected from being destroyed while they wait, so they can be ready to work again.

Researchers have now uncovered a specific chemical tag that acts as a shield for two key members of this construction team, ensuring they survive the stress and can return to their jobs. The study focuses on a process called NEDDylation, where a small protein marker is attached to other proteins to change their behavior or location. By mapping out which proteins carry this marker during normal conditions and during stress, the team identified two essential factors, known as eIF3g and eIF3i, as high-confidence targets. These factors are part of the initiation complex that starts protein production. The researchers found that under normal circumstances, these factors carry the NEDDylation tag, but when the cell is stressed by arsenite, the amount of this tag on the complex drops. Despite this drop, the tagged versions of these factors are the ones that successfully enter the stress granules.

The investigation revealed that the physical structure of one of these factors, eIF3g, is vital for this process. Only the full-length version of eIF3g, which includes a specific region called the RRM domain, is recruited into the stress granules. When the researchers tested a version of eIF3g missing this RRM domain, they found it strongly blocked the formation of stress granules, acting as a disruptive element. In contrast, the RRM domain by itself did not enter the granules and did not stop them from forming. This suggests that the complete, intact structure is required for the factor to play its proper role in the cell's emergency response.

To understand the importance of the NEDDylation tag, the team interfered with the cellular pathway responsible for adding these markers. They used a chemical inhibitor to block the enzyme that starts the tagging process, removed other components of the tagging system, or added an enzyme that strips the tags away. In every case where the tagging system was disabled, the levels of eIF3g and eIF3i proteins fell rapidly during stress. This indicates that without the NEDDylation mark, these proteins are not just failing to enter the stress granules; they are being degraded or destroyed. The findings suggest that NEDDylation marks a specific pool of these proteins that is resistant to breakdown, allowing them to survive inside the stress granules. This mechanism links the tagging system directly to the stability of the proteins needed for translation, ensuring that when the stress ends, the cell has the necessary tools available to restart the production of proteins.