Evolution: Theoretical junk protein (Evolution)

by David Turell , Wednesday, December 09, 2020, 18:55 (1443 days ago) @ David Turell

Seems to be a replacement for junk DNA to try to support Darwin theory:

https://phys.org/news/2020-12-simple-evolution-useless-complexity.html

"A new study at the University of Chicago has shown that elaborate protein structures accumulate over deep time even when they serve no purpose, because a universal biochemical property and the genetic code force natural selection to preserve them.

"Most proteins in our cells form specific complexes with other proteins, a process called multimerization. Like other kinds of complexity in biology, multimers are usually thought to persist over evolutionary time because they confer some functional benefit that is favored by natural selection.

"'How complexity evolves is one of the great questions of evolutionary biology," said senior author Joseph Thornton, Ph.D., professor of human genetics and ecology and evolution at the University of Chicago. "The classic explanation is that elaborate structures must exist because they confer some functional benefit on the organism, so natural selection drives ever-increasing states of complexity. Clearly in some cases complexity is adaptive, like the evolution of the eye: complex eyes see better than simple ones. But at the molecular level, we found that there are other simple mechanisms that drive the build-up of complexity.

***

"Once a protein evolves to multimerize, the parts that form the interface can accumulate mutations that would be deleterious if the protein were in the solo state, so long as they can be tolerated in the multimer. Purifying selection then entrenches the complex form, preventing a return to the solo state.

"The researchers showed that a simple and universal rule of biochemistry underlies entrenchment. Proteins are made up of amino acids, which may be water soluble, or hydrophobic, meaning they dissolve easily in oil but not water. Usually, proteins fold so the water-soluble amino acids are on the outside and the hydrophobic amino acids are on the inside. Mutations that make a protein's surface more oil soluble impair its folding, so purifying selection removes them if they occur in solo proteins.

"If the protein evolves to multimerize, however, those hydrophobic amino acids on the interface surface are hidden from water, and become invisible to purifying selection. The multimer is then entrenched, because returning to the solo state would expose the now-oil-soluble and deleterious interface.

"This "hydrophobic ratchet" appears to be universal. The researchers analyzed a massive database of protein structures, including hundreds of dimers and related solo proteins, and found that the vast majority of interfaces have become so hydrophobic that the dimeric form is deeply entrenched.

"This mechanism, operating on thousands of proteins over hundreds of millions of years, could drive the gradual accumulation of many useless complexes inside cells."

Comment: This is all theoretical. If these useless proteins exist in cells they must be found, and they haven't been as yet.