Evolution of protein molecules seems to continue 3.5 billion years after it had begun. It runs on a very slow pace, but even extremely ancient proteins of different species, which come from one common ancestor, keep changing.

This phenomenon was discovered by Russian scientists, Fedor Kondrashov and Inna Povolotskaya, who are currently employed in the Centre of Genomic Regulation, Barcelona, Spain. Researchers have described their discovery in the Nature science magazine.

Biological chemistry knows many proteins, and so-called conservative proteins are among them. This term means that proteins, belonging to various species of living beings, but performing same functions in these organisms, have similar amino acid sequences or structural patterns. Even in evolutionally distant species these proteins can show up to 40% of similarity.

Biologists tend to think that conservative sequences have stayed unchanged during evolution, because they are responsible for some special protein functions. However, they might be wrong, and these molecules could have had much more difference. They simply haven’t had enught time for that.

 

 

While studying protein evolution, Fedor Kondrashov and Inna Povolotskaya got inspired by an American astronomer Edwin Hubble, who, in 1929, fund out that galaxies moved away from each other with velocities, directly depending on distance between them. Scientists of the Centre of Genomic Regulation used the same approach to proteins – they compared sequences of 572 proteins, belonging to 836 species of microorganisms, including those, which had existed before time. Aim of the comparison was finding difference in sequences of these proteins, or distances, and how fast were these changes introduced into sequence.

Hubble’s calculations revealed that our Universe was born in a Big Bang, and that galaxies still keep flying away from the Big Bang’s centre. Studies, performed in Barcelona, allow suggesting that there was a single ancestor of all living organisms. Species, originating from this ancestor, inherited his proteins, which have, of course, changed due to 3.5 billion years of evolution, but still have some thing in common. However, the process of evolution hasn’t finished yet, and these proteins can and will change, thus gaining more and more difference from each other and from their common ancestor.

This phenomenon was called a “Big Bang” in a “protein universe”. The centre of this bang is a common ancestor, and changes in proteins of his descendant species is like recession of galaxies.

There were plenty of living organisms on our planet for past 3.5 billion years. Why some ancient proteins change so slowly? A protein molecule is an amino acid sequence, which is folded in some specific way. Changes in these molecules mean that one amino acid is replaced with another. Such replacements do happen from time to time, but 98% of them result in wrong folding of a protein molecule and failure to perform its functions. Such changes go directly into a rubbish bin. Sometimes, due to such changes, a protein molecule steps back, or becomes more like an ancestor’s protein. That is why “protein universe” expands so slowly.

Modern bioengineering techniques allow calculating all changes that proteins can bear without losing its functions. These calculations show that this limit isn’t yet reached. Proteins can still change, and their evolution keeps going on.

Sources: Science & Technologies

I. S. Povolotskaya, F. A. Kondrashov «Sequence space and the ongoing expansion of the protein universe», Nature, 17 June 2010, Vol. 465, ¹ 09105

Kizilova Anna