IISc team finds ancient proteins that hint at life’s leap in complexity

One of biology’s biggest mysteries is how simple cells evolved into the complex cells we see in animals, plants, and fungi. Simple cells like bacteria and archaea usually have fewer parts and simpler machinery. Eukaryotic cells, on the other hand, have elaborate internal structures and complicated systems for dividing and maintaining their shape.

To understand how this transition happened, scientists study a special group of archaea called the Asgard archaea. These microbes are considered the closest living relatives of eukaryotes and their genes provide important clues about how complexity first arose.

A key piece of this puzzle is the cytoskeleton, the network of proteins that gives cells their shape and helps them divide. In bacteria, the FtsZ protein is essential for cell division. Eukaryotes rely on related proteins such as tubulin, which perform more advanced functions.

In a new study published in The EMBO Journal, Indian Institute of Science researchers have reported that Odinarchaeota, a member of the Asgard group, has two versions of the FtsZ gene, along with a tubulin-like gene. This is unusual: most microbes only carry one.

The researchers analysed the two FtsZ proteins using phylogenetic studies, biochemical tests, and cryo-electron microscopy. They examined how each protein assembled in the presence of energy-carrying molecules like GTP, and tested whether they could bind to artificial membranes.

The two proteins showed distinct behaviours. OdinFtsZ1 formed straight protofilaments similar to bacterial FtsZ and could anchor directly to membranes. OdinFtsZ2 formed unusual spiral ring-like structures and needed the help of an adaptor protein to attach to membranes. When both proteins were tested together, they interacted, suggesting they may cooperate in actual cells.

The differences point to a division of labour between the two paralogs. This means cytoskeletal proteins in archaea can divide into specialised roles, a sign of growing cellular complexity. The combination of two FtsZ systems and a tubulin-like protein indicates Asgard archaea were experimenting with many structural strategies, possibly foreshadowing the diverse cytoskeletal machinery of eukaryotes.

“These proteins give us a rare snapshot of a turning point in evolution, where life began building the dynamic skeleton that supports all higher organisms today,” project lead Saravanan Palani told The Hindu. He added that next, the team will grow Asgard microbes in the lab to “observe these proteins in living cells, potentially offering a real-time view of one of evolution’s greatest leaps.”