By Odin’s Beard! Tubulins named after the Norse god could be the missing link between single-celled organisms and human cells

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A team of researchers from Nagoya University in Japan may have discovered a missing link between bacterial cells and animal and plant cells, including those of humans. They named it Odin’s Tubulin.

The origin of tubulin is crucial to understanding the process of eukaryogenesis, when animal and plant cells separate from bacteria. In animal and plant cells, tubulin forms microtubules essential to their internal organization. Tubulin supports the cell by giving it structure, shape and internal organization. Because it is so essential to the cell, discovering the origin of tubulin would be a remarkable step in understanding how the complex cells found in animals and plants diverged from individual cells in bacteria.

Archaeons of the Archaea superphylum of Asgard are crucial for this research because scientists consider them to be the closest single-celled cells to animal and plant cells. Although these microscopic unicellular organisms resemble bacteria, they differ in their genetic composition and cellular structure. Thus, as an intermediary between bacteria and animal/plant cells, scientists regularly use them to understand the evolution of animal/plant cell characteristics.

In a study published in Scientists progressa group led by Akihiro Narita, Associate Professor, Division of Biological Sciences, Nagoya University, Graduate School of Science, in collaboration with Tokyo Institute of Technology, Okayama University, and Institute of Science of terrestrial life, used X-rays to study a protein tubulin homolog of the archaeon Odinarchaeota whose name comes from Odin, a god of Norse mythology.

“Its filamentary structure was surprising. The diameter was 100 nanometers, which is much larger than eukaryotic microtubules,” says Narita. “The architecture was also unique. Molecules polymerize into arcs, which are then assembled into a slinky-like coil. We can consider this coil structure as an evolutionary intermediary between FtsZ, a bacterial homolog of tubulin that also polymerizes into rings, and tubulin occurs in plant and animal cells.

Professor Narita’s group also explained how tubulin could have evolved. They hypothesize that it appeared before the origin of plant/animal cells. Segregation of increasing size chromosomes and enlargement of cell size during eukaryogenesis may have necessitated the development of stiffer tubules to navigate increasing cell distances and/or payloads. This may have produced an evolutionary pressure that encouraged the shift from a flexible type to a stiffer parallel protofilament pattern seen in microtubules.

Professor Narita is excited about the implications of their findings. He says: “We think it’s very likely that microtubules are in the middle of the evolutionary process. This discovery reveals part of how eukaryotes – including us – came to be.”

Funding was provided by JST CREST, Japan (grant number JPMJCR19S5); Japan Society for the Promotion of Science (grant number JP20H00476); and the Moore-Simons Project on the Origin of the Eukaryotic Cell (grant number GBMF9743), as well as by the ELSI-First Logic astrobiology donation program.

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Material provided by Nagoya University. Note: Content may be edited for style and length.

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