Amazing stuff!
I have recently blogged here that the Asgard archaea were already linked to the Eukaryotic Immune System.
"Ten years ago, nobody knew that Asgard archaea even existed. In 2015, however, researchers examining deep-sea sediments discovered gene fragments that indicated a new and previously undiscovered form of microbes. ...
After a further search, microbiologists identified the corresponding organisms, described them and classified them as a separate archaeal sub-group: Asgard archaea. ...
They turned out to be a missing link between archaea and eukaryotes—that is, between archaea and organisms whose cells contain a nucleus, such as plants and animals. ..."
From the highlights and absract:
"Highlights
• Asgard archaea express tubulins related to eukaryotic α/β-tubulin and bacterial BtubA/B
• Asgard tubulins (AtubA/B/B2) assemble into canonical and non-canonical heterodimers
• Asgard tubulin heterodimers polymerize into 5 or 7 protofilament microtubules
• AtubA/B form cytoskeletal structures in Ca. Lokiarchaeum ossiferum
Summary
Microtubules are a hallmark of eukaryotes. Archaeal and bacterial homologs of tubulins typically form homopolymers and non-tubular superstructures. The origin of heterodimeric tubulins assembling into microtubules remains unclear.
Here, we report the discovery of microtubule-forming tubulins in Asgard archaea, the closest known relatives of eukaryotes. These Asgard tubulins (AtubA/B) are closely related to eukaryotic α/β-tubulins and the enigmatic bacterial tubulins BtubA/B. Proteomics of Candidatus Lokiarchaeum ossiferum showed that AtubA/B were highly expressed.
Cryoelectron microscopy structures demonstrate that AtubA/B form eukaryote-like heterodimers, which assembled into 5-protofilament bona fide microtubules in vitro.
The additional paralog AtubB2 lacks a nucleotide-binding site and competitively displaced AtubB. These AtubA/B2 heterodimers polymerized into 7-protofilament non-canonical microtubules. In a sub-population of Ca. Lokiarchaeum ossiferum cells, cryo-tomography revealed tubular structures, while expansion microscopy identified AtubA/B cytoskeletal assemblies.
Our findings suggest a pre-eukaryotic origin of microtubules and provide a framework for understanding the fundamental principles of microtubule assembly."
Microtubules in Asgard archaea (open access)
Redrawing the tree of life, with eukaryotes descending from Asgard archaea
Graphical abstract
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