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Motiliy in the third domain of life: the haloarchaeal way to move

Final Report Summary - ARCHAEAL MOTILITY (Motiliy in the third domain of life: the haloarchaeal way to move)

Background: Motility is important for all living organisms. It allows them to move to environments with optimal conditions for growth (such as temperature, nutrient availability, ect). Members of the three domains of life, archaea, bacteria and eukaryotes have developed different structures to achieve motility. Archaea and bacteria both use a rotating filament to propel themselves forward. Their functions are similar, however the structure of these filaments is fundamentally different. The motility structure of archaea is composed of proteins with homology to type IV pili. To distinguish it from its bacterial counterpart it is named the archaellum. Via horizontal gene transfer archaea have received the chemotaxis machinery that is in bacteria responsible for the transfer of environmental signals to the base of the motility structure, which results in a change of direction of rotation. As the motility structures of archaea and bacteria are so different it is surprising that the bacterial chemotaxis components, notably the CheY response regulator protein, can still bind to the archaeal motility structure.
Therefore, the objective of this project is to identify subunits of the archaellum important for rotational switching. This information can be used to design a model how archaea can achieve directional movement.
Results: To meet the objective a new model system was established in the laboratory of Prof Albers. We opted for a euryarchaeal model, as it has both the archaellum and a chemotaxis system. The halophile Haloferax volcanii was chosen because of the good microscopy and genetic tools available for this system. We used this model to construct various genetic knock-outs and studied their phenotype on semi-solid agar plates to determine their ability for directional movement. Their swimming behavior was studied with thermomicroscopy at 45 °C, the native growth temperature of H.volcanii. In addition, we created several mutants of the chemotaxis protein, CheY, with amino acid substitution and also studied their phenotype. This showed the mechanism of action of the central chemotaxis protein, CheY, is generally conserved between bacteria and archaea. However, the crystal structure of CheY also revealed some specific structural adaptations to allow for binding with archaeal specific partners of the chemotaxis system.
Conclusion: Conclusively, archaeal CheY proteins conserved the central mechanistic features between bacteria and archaea, but evolved towards a new archaellum specific interaction partner. Therefore the chemotaxis systems represents an adaptive evolutionary plug-and-play device.

Impact: The knowledge obtained in the course of this project has contributed to mapping the diversity of the motility machinery amongst archaea and as such impacts has broad impact:
1) Due to the homology of the archaellum with bacterial type IV pili the obtained knowledge is also helping to understand the mechanism of type IV pili formation. Since type IV pili are crucial for the pathogenicity of many Gram negative bacteria, this research might help to develop possible strategies to fight infectious bacteria and prevent their invasion of eukaryotic hosts.
2) While initially all archaea were believed to be extremophilic, research in the past decade has led to the realization that archaea can be found nearly in all habitats, including the human gut. Knowledge on archaeal motility is highly relevant, because a changed motility potential of cells has high importance in the development of several clinical symptoms and syndromes. Altered chemotactic activity of pathogens can be a clinical target. Alteration of motility potential of microorganisms with pharmaceutics can decrease infections or spreading of infectious diseases.
3) The archaellum contains only few subunits, and this system represents one of the smallest biological motors. This project has enablee us to obtain valuable basic knowledge, but also contributes information required to employ this latter to develop a nano-motor for future biotechnological applications.