KEY POINTS:
Scientists have traced the origins of stress in a study that has recreated the ancient protein molecule that allows the human body to cope with demanding situations.
The molecule is the "receptor protein" which binds to the stress hormone cortisol like a key fits into a lock.
The scientists found that it evolved from a similar protein used in primitive fish that lived 450 million years ago.
By studying a range of present-day protein receptors for cortisol and related steroid hormones, the researchers were able to go back in time and rebuild the common ancestral molecule that gave rise to them all.
In effect, the scientists have been able to wind back the clock of evolution to study the precise mutations that led to the long evolution of one of the many key proteins of the body.
"Never before have we seen so clearly, so far back in time," said Joseph Thornton of the University of Oregon, who led the study published in the journal Science.
"We were able to see the precise mechanisms by which evolution moulded a tiny molecular machine at the atomic level, and to reconstruct the order of events by which history unfolded," Dr Thornton said.
The scientists studied the genes of 60 steroid receptors from present-day organisms and computed the likely genetic sequence of the common ancestral gene - and the time when it existed.
From this they reconstructed the gene itself and used it in the laboratory to make the ancestral protein, which could be studied using X-rays to determine its precise three-dimensional structure.
Further tests shows that the protein acted as a good receptor for the steroid hormones that are not involved in stress control.
This suggested that the protein's evolution into a stress-related receptor molecule occurred later on in evolutionary history.
By studying the precise position of the 2,000 atoms within the protein molecule, the scientists were able to recreate the seven changes or mutations in the protein's structure over the 450-million-year period that led to today's versions.
"This is the ultimate level of detail. We were able to see exactly how evolution tinkered with the ancient structure to produce a new function that is crucial to our own bodies today.
Nobody has done that before," Dr Thornton said.
Some of the mutations caused dramatic alterations in the molecule's structure, but others appear to be merely "permissive", not on their own causing radical changes but which were nevertheless essential for more important mutations.
"These permissive mutations are chance events. If they hadn't happened first, then the path to the new function could have become an evolutionary road not taken," Dr Thornton said.
"Imagine if evolution could be rewound and set in motion again - a very different set of genes, functions and processes might be the outcome," he said.
- INDEPENDENT
