A groundbreaking study has revealed that two essential proteins in our immune system, viperins and argonautes, can be traced back to a group of ancient microbes known as Asgard archaea. These microbes, which are more closely related to plants and animals (eukaryotes) than bacteria, are believed to have been the ancestors of all complex life on Earth. This discovery sheds new light on the evolution of our immune system and the remarkable resilience of life on our planet.
The tree of life is divided into three major domains: Bacteria, Eukarya, and Archaea. Bacteria are simple, single-celled organisms without a nucleus. Eukaryotes, on the other hand, have a nucleus where their DNA is stored, and they contain specialized organelles that perform specific functions. Archaea, though microscopic and complex, lack nuclei and organelles, but share some energy-producing mechanisms with eukaryotes.
In 2015, scientists discovered a new superfamily of archaea called Asgard archaea, which bridged the gap between bacteria and eukaryotes. These microbes, named after the mythical realm of Asgard in Norse mythology, were found in a deep-sea hydrothermal vent in the Arctic known as Loki’s castle. This discovery revolutionized our understanding of the evolution of complex life.
Further research suggested that all eukaryotes, including humans, evolved from Asgard archaea that lived around 2 billion years ago. To delve deeper into the origins of complex life, a team of scientists, led by Brett Baker, an associate professor at the University of Texas at Austin, analyzed thousands of genomes across the tree of life, identifying tens of thousands of viral defense systems. Their analysis focused on genes coding for two classes of proteins: viperins and argonautes.
Viperins, first identified in humans, are part of our innate immune system, acting as a first line of defense against a wide array of viruses, including hepatitis C and HIV. They prevent viruses from producing copies of their proteins within infected cells. Argonautes, originally discovered in squid-like plants, block viruses from replicating by chopping up their genetic material.
The researchers found that the genes for both viperins and argonautes were present across all domains of life. However, the genes were much more similar between archaea and eukaryotes than between bacteria and the other two domains. Notably, the catalytic sites, the crucial parts of the proteins responsible for their function, had changed very little over the 2 billion years since eukaryotes evolved. This remarkable stability suggests that these proteins were inherited from a common ancestor, an ancient Asgard archaean.
The study, published in the journal Nature Communications, provides compelling evidence that these two crucial immune proteins originated from Asgard archaea. The remarkable conservation of their catalytic sites over billions of years highlights their effectiveness in fighting off viral threats. This research is just the beginning. The team is now searching for other defense systems within these ancient microbes, hoping to further unravel the secrets of our immune system and the evolution of life on Earth.
