Building a flagellum (Introduction)

by David Turell , Tuesday, October 27, 2020, 22:01 (1276 days ago) @ David Turell

New steps are added to the fifty known:

https://phys.org/news/2020-10-sweet-flagellar.html

"To build the machinery that enables bacteria to swim, over 50 proteins have to be assembled according to a logical and well-defined order to form the flagellum, the cellular equivalent of an offshore engine of a boat. To be functional, the flagellum is assembled piece by piece, ending with the helix called flagellar filament, composed of six different subunits called flagellins. Microbiologists from the University of Geneva (UNIGE) have demonstrated that adding sugar to the flagellins is crucial for the flagellum's assembly and functionality. This glycosylation is carried out by a newly discovered enzyme FlmG, whose role was hitherto unknown. Based on this observation—which you can read all about in the journal eLife—the researchers followed up with a second discovery published in Developmental Cell. Among the six flagellins of Caulobacter crescentus, the model bacterium in the two studies, one is the special one serving a signaling role to trigger the final assembly of the flagellum.

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"Viollier's research team succeeded in demonstrating that the glycosylation of the six flagellins that make up the filament is essential for the formation and functionality of the flagellum. "To demonstrate this, we first identified the gene that produces the glycosylation enzyme, FlmG. When it's absent, it results in bacteria without flagellum. Secondly, we genetically modified another type of bacterium, Escherichia coli, to express one of the six flagellins, the glycosylation enzyme and sugar producing enzymes from Caulobacter crescentus. All these elements are required to obtain a modified flagellin," adds Nicolas Kint.

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"'The different elements of the flagellum are produced one after the other: the molecules of the base first, then those of the rotor and finally the propeller. The scientific literature indicates that this sequential process is important. However, we don't know how the order of manufacturing the sub-units is controlled ." The researcher and his team focused on the synthesis of the six flagellins, discovering a black sheep among them: a sub-unit that has only 50% sequence homology with the other five. "This sub-unit serves as become a checkpoint protein, a repressive molecular traffic cop restraining the synthesis of the other flagellin proteins," says Professor Viollier. It is present before the synthesis of the other five sub-units, and it acts as a negative regulator. As long as it is present in the cytosol, the synthesis of the other sub-units is prevented. Once the elements of the flagellum are assembled, apart from the filament, the cop is exported to the membrane and thus removed. Then the synthesis of the last five sub-units can then begin. "It is a sensor for the protein synthesis and a component of the flagellar filament at the same time: a dual function that is unique of its kind," says the microbiologist with great enthusiasm."

Comment: An irradicably complex assembly system. How vould this develoop by c hance. Design required.