The idea that protein folds are highly refined and profoundly flexible machines is supported by the fact that there are so few of them. Scientists have identified only about 1,000 folds and 1,500 fold superfamilies across all the organisms for which full genomes have been sequenced. Many of these protein folds are found in every organism. Other folds appear only in certain subsets of organismal life.
The Illinois teams findings add a new dimension to a long and contentious debate about the earliest stages of evolutionary divergence. By looking at protein architectures across all organisms for which genomic information is available, the team found evidence that the archaeal microbes, the one-celled organisms that inhabit some of the most forbidding environments on the planet, were the first to emerge as an evolutionarily distinguishable group. Their evidence: The repertoire of architectures that would one day belong to the superkingdom known as the Archaea was the first to lose a fold. That fold, a huge class of protein fold superfamilies, simply disappeared from the archaeal lineage altogether.
Eventually, more and more folds joined the list of architectures abandoned by the Archaea, in what the authors describe as a process of reductive evolution. The folds belonging to organisms that eventually evolved into what we now call bacteria and the multicellular eukaryotes also began to lose folds, but they started downsizing their repertoires much later than the Archaea.
Prior to this, the authors write, the world of protein folds was large and diverse, containing many of the fold architectures still in use today. This was the time of the communal ancestor, before the emergence of superkingdoms and the myriad organisms that would eventually populate each group.
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign