Evolution of Complexity Recreated Using 'Molecular Time Travel'
ScienceDaily (Jan. 8, 2012) — Much of what living cells do is carried out by "molecular machines" -- physical complexes of specialized proteins working together to carry out some biological function. How the minute steps of evolution produced these constructions has long puzzled scientists, and provided a favorite target for creationists.
Rendering of DNA. Much of what living cells do is carried out by "molecular machines" -- physical complexes of specialized proteins working together to carry out some biological function. How the minute steps of evolution produced these constructions has long puzzled scientists, and provided a favorite target for creationists. (Credit: © Attila Németh / Fotolia)
In a study published early online on January 8, in Nature, a team of scientists from the University of Chicago and the University of Oregon demonstrate how just a few small, high-probability mutations increased the complexity of a molecular machine more than 800 million years ago. By biochemically resurrecting ancient genes and testing their functions in modern organisms, the researchers showed that a new component was incorporated into the machine due to selective losses of function rather than the sudden appearance of new capabilities.
"Our strategy was to use 'molecular time travel' to reconstruct and experimentally characterize all the proteins in this molecular machine just before and after it increased in complexity," said the study's senior author Joe Thornton, PhD, professor of human genetics and evolution & ecology at the University of Chicago, professor of biology at the University of Oregon, and an Early Career Scientist of the Howard Hughes Medical Institute.
"By reconstructing the machine's components as they existed in the deep past," Thornton said, "we were able to establish exactly how each protein's function changed over time and identify the specific genetic mutations that caused the machine to become more elaborate."
The study -- a collaboration of Thornton's molecular evolution laboratory with the biochemistry research group of the University of Oregon's Tom Stevens, professor of chemistry and member of the Institute of Molecular Biology -- focused on a molecular complex called the V-ATPase proton pump, which helps maintain the proper acidity of compartments within the cell.
One of the pump's major components is a ring that transports hydrogen ions across membranes. In most species, the ring is made up of a total of six copies of two different proteins, but in fungi a third type of protein has been incorporated into the complex.
To understand how the ring increased in complexity, Thornton and his colleagues "resurrected" the ancestral versions of the ring proteins just before and just after the third subunit was incorporated. To do this, the researchers used a large cluster of computers to analyze the gene sequences of 139 modern-day ring proteins, tracing evolution backwards through time along the Tree of Life to identify the most likely ancestral sequences. They then used biochemical methods to synthesize those ancient genes and express them in modern yeast cells.
Thornton's research group has helped to pioneer this molecular time-travel approach for single genes; this is the first time it has been applied to all the components in a molecular machine.
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Evolution of increased complexity in a molecular machine
Gregory C. Finnigan, Victor Hanson-Smith, Tom H. Stevens & Joseph W. Thornton
Nature (2012) doi:10.1038/nature10724
Nature (2012) doi:10.1038/nature10724
Received 21 September 2011 Accepted 21 November 2011
Published online 09 January 2012
Many cellular processes are carried out by molecular ‘machines’—assemblies of multiple differentiated proteins that physically interact to execute biological functions1, 2, 3, 4, 5, 6, 7, 8. Despite much speculation, strong evidence of the mechanisms by which these assemblies evolved is lacking. Here we use ancestral gene resurrection9, 10, 11 and manipulative genetic experiments to determine how the complexity of an essential molecular machine—the hexameric transmembrane ring of the eukaryotic V-ATPase proton pump—increased hundreds of millions of years ago. We show that the ring of Fungi, which is composed of three paralogous proteins, evolved from a more ancient two-paralogue complex because of a gene duplication that was followed by loss in each daughter copy of specific interfaces by which it interacts with other ring proteins. These losses were complementary, so both copies became obligate components with restricted spatial roles in the complex. Reintroducing a single historical mutation from each paralogue lineage into the resurrected ancestral proteins is sufficient to recapitulate their asymmetric degeneration and trigger the requirement for the more elaborate three-component ring. Our experiments show that increased complexity in an essential molecular machine evolved because of simple, high-probability evolutionary processes, without the apparent evolution of novel functions. They point to a plausible mechanism for the evolution of complexity in other multi-paralogue protein complexes.
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NOTA DESTE BLOGGER:
Esta pesquisa é uma tentativa de falsificar a complexidade irredutível de Michael Behe que respondeu prontamente com um artigo A Blind Man Carrying a Legless Man Can Safely Cross the Street: Experimentally Confirming the Limits to Darwinian Evolution [Um homem cego carregando um homem sem pernas pode atravessar a rua com segurança: confirmando experimentalmente os limites da evolução darwiniana].