An article from Science Daily highlights a recent study which looks, not at the specific sequences of proteins, but instead their functional parts to trace back their evolution, and the sheds light on the differentiation of the 3 superkingdoms: Bacteria, Archaea, and Eukarya
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All proteins contain domains that can be identified by their structural and functional similarities to one another. These domains are the gears and motors that allow the protein machinery to work. Every protein has one or more of them, and very different proteins can contain the same, or similar, domains. By conducting a census of all the domains that appear in different groups of organisms and comparing the protein repertoires of hundreds of different groups, the researchers were able to construct a timeline of protein evolution that relates directly to the history of life.
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Unlike the sequence of amino acids in a protein, which is highly susceptible to change, the protein modules found today in living organisms have endured because they perform critical tasks that are beneficial to the organisms that host them, Caetano-Anolls said.
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By tracing the history of the modules, the researchers were able to build a rough timeline of protein evolution. It revealed that before the three superkingdoms began to emerge, most proteins contained only single domains that performed a lot of tasks.
"As time progressed, these domains started to combine with others and they became very specialized," Caetano-Anolls said. This eventually led to the big bang of protein architectures.
"Exactly at the time of the big bang," he said, many of the combined domains began to split apart, creating numerous single-domain modules again. But these new modules were much more efficient and specialized than their ancient predecessors had been.
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