Aging found protein cause | Science and life


Aging is described in different ways, depending on whether we consider the body as a whole, individual organs, cells, or go down to the level of molecules. Accordingly, we get a whole set of causes of aging; if you look from the point of view of molecular biology and biochemistry, then this is the accumulation of mutations in DNA that the cell can no longer correct, and epigenetic modifications that change the activity of genes, and background oxidative stress, which increases due to the fact that antioxidant systems begin to work is getting worse, and the appearance of a large number of misfolded proteins.

Of course, all these reasons are closely related to each other, in addition, the question always arises why this happens, that is, what are the reasons of a deeper order. For example, we talked about misfolded proteins. It is known that any protein works only in the desired spatial form: the amino acids in the polypeptide chain interact with each other, tighten and twist different parts of the protein molecule, and as a result, the protein folds into a complex lump, or a complex thread, or into a long flat sheet. But it happens that the folding goes wrong, and the protein not only cannot fulfill its direct duties, it sometimes begins to harm: toxic complexes of incorrectly folded molecules are formed in the cell, because of which it starts to get sick and eventually dies. The most famous examples here are neurodegenerative diseases such as Alzheimer’s disease. But in general, the accumulation of misfolded proteins in the cell (not necessarily related to Alzheimer’s disease, etc.) is one of the common signs of aging. Why are they piling up?

The reason is not necessarily mutations that cause proteins to fold incorrectly. The cell has special garbage collection systems that promptly rid it of such proteins – with age, such systems increasingly fail. Another explanation is changes in the redox potential where proteins fold, that is, in the cell’s endoplasmic reticulum. Employees Stanford University offer another option – in an article in Nature they write that age-related defects in the folding (or folding) of protein molecules begin even during their synthesis on ribosomes.

As we know, ribosomes are such large and complex molecular complexes that travel along messenger RNA (mRNA) and assemble a polypeptide chain from amino acids. Ribosomes read the protein code copied from DNA into mRNA, and in accordance with what they read, they take this or that amino acid and combine it with the previous one (there are many features and subtleties that we will now omit). Many ribosomes move along one mRNA at the same time, and they move quite quickly. A growing polypeptide chain hangs from each ribosome, which begins to fold as it grows: the synthesized protein tries to enter the correct, functional 3D conformation.

Researchers have observed what happens to protein synthesis in aging yeast and nematode worms Caenorhabditis elegans. It turned out that with age, ribosomes begin to periodically slow down and often collide with each other (that is, the back one catches up with the front one). The appearance of a larger number of incorrectly folded protein molecules is associated precisely with ribosomal inhibitions and collisions: amino acids in the growing polypeptide chain establish incorrect contacts with each other. And even if the proportion of incorrectly folded proteins is small – only about 10% of all synthesized polypeptide chains, this will already be enough for the garbage collection system to stop coping with them and non-working and dangerous protein molecules begin to accumulate in the cell. (Protein synthesis takes place on the membranes of the endoplasmic reticulum, so a redox imbalance explanation may add to the overall picture.)

Since protein synthesis on ribosomes (or translation) is one of the most fundamental processes of life, and in all eukaryotes, which include worms, yeast, and humans, translation is more or less similar, then, most likely, something happens in aging human cells. same thing. True, another question arises here: why, in fact, do ribosomes begin to slow down with age? Each ribosome is a huge complex of several special RNAs and eight dozen proteins sitting on these RNAs; in addition, other service RNAs and proteins also participate in translation. Which of them is to blame for slowing down the ribosome and why? So far, there is no answer here. However, it is known that if yeast acquires life-prolonging mutations – and some of these mutations are well studied – then yeast ribosomes return to normal. Probably, these mutations can be used to begin to decipher the mechanism of ribosome aging.


Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.

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