Archaeal flagellin combines a bacterial type IV pilin domain with an Ig-like domain

Tatjana Braun, Matthijn R. Vos, Nir Kalisman, Nicholas E. Sherman, Reinhard Rachel, Reinhard Wirth, Gunnar F. Schröder*, Edward H. Egelman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


The bacterial flagellar apparatus, which involves ∼40 different proteins, has been a model system for understanding motility and chemotaxis. The bacterial flagellar filament, largely composed of a single protein, flagellin, has been a model for understanding protein assembly. This system has no homology to the eukaryotic flagellum, in which the filament alone, composed of a microtubule-based axoneme, contains more than 400 different proteins. The archaeal flagellar system is simpler still, in some cases having ?13 different proteins with a single flagellar filament protein. The archaeal flagellar system has no homology to the bacterial one and must have arisen by convergent evolution. However, it has been understood that the N-terminal domain of the archaeal flagellin is a homolog of the N-terminal domain of bacterial type IV pilin, showing once again how proteins can be repurposed in evolution for different functions. Using cryo-EM, we have been able to generate a nearly complete atomic model for a flagellar-like filament of the archaeon Ignicoccus hospitalis from a reconstruction at ∼4-Å resolution. We can now show that the archaeal flagellar filament contains a β-sandwich, previously seen in the FlaF protein that forms the anchor for the archaeal flagellar filament. In contrast to the bacterial flagellar filament, where the outer globular domains make no contact with each other and are not necessary for either assembly or motility, the archaeal flagellin outer domains make extensive contacts with each other that largely determine the interesting mechanical properties of these filaments, allowing these filaments to flex.

Original languageAmerican English
Pages (from-to)10352-10357
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number37
StatePublished - 13 Sep 2016

Bibliographical note

Funding Information:
We thank Michael Thomm, Harald Huber, Thomas Hader, and Konrad Eichinger for support in using the fermentation facility of the Archaea Centre Regensburg to grow Ignicoccus cells at large scale. This work was initially supported by Deutsche Forschungsgemeinschaft Grant WI 731/10-1 (to R.R. and R.W.) and also supported by NIH Grant EB001567 (to E.H.E.). The W. M. Keck Biomedical Mass Spectrometry Laboratory is funded by a grant from the University of Virginia's School of Medicine.


  • Archaea
  • Cryo-EM
  • Flagellar filaments
  • Helical polymers


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