Tubulin Odin helped to understand the evolution of nuclear cells

(ORDO NEWS) — Eukaryotes, or nuclear, are the most complex of living cells, giving rise to all multicellular creatures. Biologists have learned more about their origin through the study of Odin’s tubulin, a protein in the cellular skeleton of one of the “Asgardian archaea”, the closest relatives of eukaryotes.

Modern biologists divide all living things into three groups according to the type of cell organization – these are the so-called domains of life.

The first includes bacteria, simply arranged microbes without a nucleus. The second domain is eukaryotes, complex cells with a nucleus and other organelles, which include various protists and all multicellular organisms (including plants and animals).

The third group was identified much later than others – these are archaea (they were also called archaebacteria before), strongly resembling bacteria in size and cell structure.

They are also very small, always unicellular and devoid of a nucleus. However, when scientists learned more about the structure of archaea at the molecular level, they were surprised: these cells combine the individual properties of both bacteria and eukaryotes.

In fact, archaea became the progenitors of all eukaryotes, including humans. At the dawn of evolution, more than 2.7 billion years ago, one of the most important and enduring symbioses began.

Then some bacteria settled inside a large archaea, becoming its mitochondria (later also plant chloroplasts) – and the first nuclear cells arose. It turns out that all animals and plants are “inhabited” by ancient microbes that have become an integral part of them.

An important milestone in the understanding of these ancient events was the discovery of asgardarchei, that is, “archaeus from Asgard.”

Asgard is the walled city of the gods in Norse mythology. Such archaea are the closest relatives of eukaryotes and have common features with them. Separate groups of these “cousins” of eukaryotes were named after the Scandinavian gods Loki, Thor, Odin and Heimdall.

The focus of a new study by Japanese scientists was odinarchae – part of the single-celled Asgard, named after Odin – the supreme deity, shaman and sage.

The authors of the Science Advances article focused on one of the Odinarchae proteins found in black smokers, Odin tubulin. Tubulin forms long microtubules, part of the cell skeleton. a kind of “cellular reinforcement”, which is needed to maintain the shape of the cell, its division and directed transport of substances.

The emergence of tubulin was an important step on the way to the complication of cells and their eukaryotization – the transition to a nuclear structure.

Only thanks to it, all multicellular creatures appeared on Earth, including plants, fungi and animals. As a rule, bacteria and archaea lack tubulin, but odinarchaea, as it turned out, have a protein similar to it (that is, homologous) – Odin tubulin.

Tubulin Odin helped to understand the evolution of nuclear cells
The place of the asgardarchei in the living system

Biochemists have carefully examined it using cryoelectron microscopy, specific dyes and molecular modeling. They paid special attention to the process of microtubule assembly and were able to draw some rather unexpected conclusions.

“The structure of its filament [a filamentous complex formed by Odin’s tubulin — Ed.] was unexpected. The diameter was 100 nanometers, which is much larger than that of eukaryotic tubulin,” shared Akihiro Narita from Nagoya University (Japan).

The architecture is also unique. The molecules first polymerize into small arcs and then assemble into something like a helical spring. We can consider this structure as a transitional link in evolution between FtsZ (a homologue of tubulin in bacteria, which is also able to polymerize in the form of rings) and plant and animal tubulin.”

The authors conclude that functional tubulin arose for the first time in one archaeota and, by and large, was inherited by eukaryotes in its finished form.

It turns out that tough and durable tubulin appeared before the first nuclear cells and became their important prerequisite. This could be due to the increase in the genome of ancient cells – in the process of division, they had to move more and more loads over long distances.

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