(ORDO NEWS) — Most biological processes are carried out by complex protein complexes that work together. The evolution of such structures is one of the greatest mysteries of modern biology, because the intermediate forms from which they arose no longer exist.
An international team of researchers led by the professor at the University of Chicago, Joseph Thornton, has established that such structural complexity can arise due to very simple mechanisms. Researchers have identified an evolutionary “missing link,” whereby hemoglobin, a multicomponent molecule that carries oxygen in the blood of most vertebrates, emerged from simple precursors.
According to scientists, for the appearance of hemoglobin, only two mutations were needed, which happened about 400 million years ago. An article about this discovery was published in Nature .
Hemoglobin consists of four protomeric parts. In an adult, they are represented by two α and two β chains of polypeptides. The protomers form a ring-like structure, in the center of which is the heme – a complex of protoporphyrin with an iron atom. Interestingly, other protein molecules structurally similar to hemoglobin polypeptide chains do not form bonds between themselves.
Using a combination of statistical and biochemical methods, Thornton and his colleagues made a “molecular journey into the past.” This allowed them to identify the missing link in the evolution of hemoglobin – a two-component complex consisting of two copies of the same protein and existed at least in the last common ancestor of man and shark.
This molecule has not yet possessed any properties that would allow it to transport oxygen. Having modeled the possible ways of changing this ancient protein, scientists found that only two mutations were enough to form a four-component complex capable of binding O 2 molecules .
The traditional view of the evolution of biological complexity suggests that this very complexity gradually increases over time through a multitude of mutations, each of which is “approved” by natural selection. A new study shows that (at least at the molecular level) new complex forms can be created very quickly.
“We were amazed when we saw that such a simple mechanism could impart such complex properties,” says Thornton. “This suggests that jumps in complexity can occur suddenly and even accidentally during evolution, creating new molecular objects that eventually become necessary for our biology.”
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