Because it is so essential to the cell, uncovering the origin of tubulin would be a remarkable step in understanding how the complex cells found in animals and plants diverged from the single cells of bacteria.
A new study says it has discovered a missing link between bacterial cells and animal and plant cells. They named it the Odin tubulin, after the Norse God of god of war, magic, and the dead. Archaeons of the Asgard archaea superphylum were used because they are the closest single-celled relative to animal and plant cells. The single-celled organisms look like bacteria but differ in genetic makeup and cell structure. As an intermediary between bacteria and animal/plant cells, scientists regularly use them to understand the evolution of the features of animal/plant cells.
In the study, a group led by Akihiro Narita, Associate Professor of Nagoya University’s Division of Biological Science, Graduate School of Science, in collaboration with Tokyo Institute of Technology, Okayama University, and the Earth-Life Science Institute, used x-rays to investigate a tubulin homolog protein from the archaeon Odinarchaeota.
“Its filament structure was surprising. The diameter was 100 nanometers, which is much wider than the microtubules of eukaryotes,” Narita explains. “The architecture was also unique. The molecules polymerize into arcs, which are then assembled into a slinky-like coil. We can view this coil structure as an intermediate in the evolution between FtsZ, a bacteria tubulin homologue that also polymerizes into rings, and the tubulin found in plant and animal cells. "
How might the tubulin have evolved? They hypothesize that it emerged before the origin of plant/animal cells. The segregation of chromosomes of increasing size and enlargement of cell size during eukaryogenesis may have required the development of stiffer tubules to navigate the widening cellular distances and/or payloads. This may have produced evolutionary pressure that encouraged a shift from a flexible type to the stiffer parallel protofilament pattern seen in microtubules.