Friday, May 18, 2007
Researchers at the University of Illinois have constructed the first global family tree of metabolic protein architecture.
...Of 776 metabolic protein folds surveyed, 16 were found to be omnipresent, and nine of those occurred in the earliest branches of the newly constructed tree. "These nine ancient folds represent architectures of fundamental importance undisputedly encoded in a genetic core that can be traced back to the universal ancestor of the three superkingdoms of life," the authors wrote. The analysis also found that the most ancient metabolic protein folds are important to RNA metabolism, specifically the interconversion of the purine and pyrimidine nucleotides that compose the core of the RNA molecule. This discovery supports the hypothesis of an RNA world in which RNA molecules were among the earliest catalysts of life. This idea is based in part on the observation that RNA still retains many of its catalytic capabilities, including the ability to make proteins. Gradually, according to this theory, proteins began taking over some of the original functions of RNA. "The most ancient (protein) molecules were involved in the interconversion of nucleotides. But they were not synthesizing them," Caetano-Anollés said. "We see that all the enzymes that were involved in purine synthesis, for example, were very recent. Since these first proteins benefited the formation of building blocks for the primitive RNA world, it makes a lot of sense that we've found this origin encased in nucleotide metabolism."
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