Modern proteins exhibit an impressive degree of structural diversity, which has been well characterized, but very little is known about how and when over the course of evolution 3D protein structures arose, reported a news agency.

"So far, attempts to understand protein structure evolution have been based on the comparison between structures of modern proteins. This is equivalent to trying to understand the evolution of birds by comparing several living birds," senior study author Jose Sanchez-Ruiz of the University of Granada said.

"But it is most useful to study fossils so that changes over evolutionary time are apparent. Our approach comes as close as possible to 'digging up' fossil protein structures," Sanchez-Ruiz added.

In the study, the researchers recreated fossil proteins known as thioredoxins in the laboratory and characterized their features. Thioredoxins were chosen because they are found in organisms from the three domains of life including bacteria, archaea and eukaryotes.

By analyzing their X-ray crystal structures, they found that present-day thioredoxin structures are remarkably similar to those that existed at a time close to the origin of life, even though their amino acid sequences are very different.

This finding supports a punctuated-equilibrium model of evolution in which protein structures remain constant over long time periods, with new changes occurring intermittently over short periods, the researchers said.


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