Mitochondria control "DNA translation"

Power plants of the cell involved in ribosome formation

Iron-sulfur center © Roland Lill
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Marburg researchers have discovered why mitochondria are "essential" for cell survival. The cell's power plants not only generate energy, they also participate in the production of the protein Rli1, which plays a crucial role in the translation of genetic information into vital proteins.

Already five years ago, Lill and co-workers, in collaboration with the Hungarian group led by Professor Gyula Kispal, found out that mitochondria are responsible for the vital formation of so-called iron-sulfur centers, which - when incorporated into proteins - can transmit electrons, for example. An important example of the function of iron-sulfur proteins is the cellular respiration of oxygen to water.

Unlike the researchers had previously suspected, the synthesis of iron-sulfur proteins is not spontaneous, but in a complex biochemical process. So far, Lill and his colleagues have discovered twelve of the twenty known, mostly mitochondrial proteins that are important for this process. If the formation of iron-sulfur proteins is suppressed, the cell dies. These components have a vital function. Thus, after many decades of mitochondrial research, it finally became possible to clarify which process makes these organelles essential components of a cell. However, it has not yet been decided which iron-sulfur protein it is exactly that makes the process of formation of these components in the mitochondria essential and what function it fulfills.

Complicated assembly machinery

In the journal of the European Molecular Biology Organization (EMBO), Lill and co-workers now report the discovery of the protein Rli1 and its function. In investigations on the model organism yeast, his group found out in collaboration with the Heidelberg group around Professor Ed Hurt that Rli1 is responsible for the production of ribosomes. These in turn are responsible for the "translation" of genetic information into proteins.

According to Lill, "One can imagine the process simplified in this way: So-called iron-sulfur centers are formed by a complicated assembly machinery with the participation of the mitochondria and used for the synthesis of the iron-sulfur protein Rli1. Rli1 has a function in the formation of ribosomes, which in turn produce proteins. Funnily, this results in a henna and egg problem. "Display

"The importance of these processes for evolution is enormous, " says Lill. "Both the ribosome biogenesis and the production of the iron-sulfur proteins must have been 'invented' very early in the genesis of life and are obviously closely linked via Rli1!"

In addition, according to the biochemist, mitochondria must be "seen in a different light now". To date, they have mostly been considered as power plants of the cell, since their best known biochemical function is cellular respiration, that is, the production of energy in the form of adenosine triphosphate (ATP).

But even without cellular respiration, a cell lives on, at least for some time, when it is "fed" with glucose, for example.

"More fundamental to the importance of mitochondria has now been found to be the process of synthesizing iron-sulfur proteins in them, " explains Lill, "because this is a prerequisite for the formation of ribosomes and so the cell is only able to read its genetic material. "

Friedreich's Ataxia

Also pathological disorders in the production of iron-sulfur proteins are known. For example, they develop in a neurodegenerative disease called Friedreich's ataxia, which occurs on average in one out of every 50, 000 people and usually leads to death from heart failure triggered by cardiomyopathy.

The rarity of this disease is an indication of the great importance of iron-sulfur protein synthesis in mitochondria, because such a basic process must function stably to be equal to evolutionary selection.

(idw - University of Marburg, 01.04.2005 - DLO)