Building a flagellum patterns: in bacteria & archaea (Introduction)

by David Turell , Tuesday, September 26, 2017, 20:27 (2616 days ago) @ Balance_Maintained

The construction of a bacterial flagellum and an Archean differ, but both propel:

https://elifesciences.org/articles/27470#abstract

"The molecular composition of the archaellum and of the motor that drives it appears to be entirely distinct from that of the functionally equivalent bacterial flagellum and flagellar motor. Yet, the structure of the archaellum machinery is scarcely known. Using combined modes of electron cryo-microscopy (cryoEM), we have solved the structure of the Pyrococcus furiosus archaellum filament at 4.2 Å resolution and visualise the architecture and organisation of its motor complex in situ. This allows us to build a structural model combining the archaellum and its motor complex, paving the way to a molecular understanding of archaeal swimming motion.

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"Together with a wealth of previous biochemical data, our new structures of the Pyrococcus furiosus archaellar motor complex, the polar cap, the S-layer, and the archaellum itself enable us to build a first model describing the architecture of the archaellum machinery (Figure 7). (go to the website to see the illustration)

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"Filament assembly and rotation is powered by the archaellar motor, which is composed of the fully membrane-embedded FlaJ, a bell-shaped cytosolic complex of FlaI and FlaH and a surrounding cytosolic ring, most likely consisting of FlaC and D/E. This ring was not observed in averages of the archaellar motor complex of Thermococcus kodakarensis, which may either be due to species-dependent structural differences of motor components or the smaller number of particles used for the T. kodakarensis average. In the periplasm, the filament is thought to be coordinated by FlaF. As no densities spanning the entire periplasm are seen in our sub-tomogram average of the motor complex , we suggest that FlaF does not form a continuous conduit that connects the membrane and the outer canopy of the S-layer. Instead, this protein may coordinate the archaellum near the membrane, while the main periplasmic part of the filament is flexibly integrated into the S-layer.

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"In its substance, our model of the archaellum and its motor complex will be universal to all motile Archaea, as the core of the archaellum machinery (FlaA/B, FlaF, FlaG, FlaH, FlaI and FlaJ) is conserved throughout crenarchaeal, euryarchaeal and thaumarchaeal lineages;

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"The ubiquity and conservation of the archaellin/T4 pilin (A/T) blueprint highlights its evolutionary success as an exquisite building block for stable, yet flexible and versatile filaments. The presence of this blueprint in Archaea and Bacteria also raises the intriguing hypothesis that a common A/T-like progenitor protein and filament existed in the last universal common ancestor (LUCA), before these two domains of life diverged more than 3 billion years ago

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"For swimming motion, Bacteria have developed the flagellar machinery, a massive double-membrane spanning macromolecular device that is thought to share a common ancestor with the bacterial type-3 secretion system (Chen et al., 2011; Erhardt et al., 2010). The evolutionary reason for the higher complexity of both, bacterial T4P assembly machines as well as flagellar motors is speculative. However, it may be hypothesised that Bacteria needed to come up with additional protein components for their T4P assembly machinery as well as an entirely different propulsion device as they developed a double membrane, which is, with very few exceptions, not found in Archaea."

Comment: It is not clear, since these two motors are so different, that there is a common ancestor or two ancestors with life starting in more than one place in more than one way. Woese believed the latter.