Biophysical Reviews

, Volume 10, Issue 2, pp 559–570 | Cite as

Bacterial flagellar axial structure and its construction

  • Katsumi Imada


The bacterial flagellum is a motile organelle composed of thousands of protein subunits. The filamentous part that extends from the cell membrane is called the axial structure and consists of three major parts, the filament, hook, and rod, and other minor components. Each of the three main parts shares a similar self-assembly mechanism and a common basic architecture of subunit arrangement while showing quite distinct mechanical properties to achieve its specific function. Structural and molecular mechanisms to produce these various mechanical properties of the axial structure, such as the filament, the hook, and the rod, have been revealed by the complementary use of X-ray crystallography and cryo-electron microscopy. In addition, the mechanism of growth of the axial structure is beginning to be revealed based on the molecular structure.


Bacterial flagellum Axial structure X-ray crystallography Cryo-electron microscopy 



The author thanks Keiichi Namba and Tohru Minamino for their encouragement and fruitful discussion. This work was partially supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology.

Compliance with ethical standards

Conflict of interest

Katsumi Imada declares that he has no conflicts of interest.

Ethical approval

This article does not contain any studies with human participants or animals performed by the author.


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© International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany, part of Springer Nature 2017

Authors and Affiliations

  1. 1.Department of Macromolecular Science, Graduate School of ScienceOsaka UniversityToyonakaJapan

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