Structure of Vibrio FliL, a New Stomatin-like Protein That Assists the Bacterial Flagellar Motor Function

Norihiro Takekawa; Miyu Isumi; Hiroyuki Terashima; Shiwei Zhu; Yuuki Nishino; Mayuko Sakuma; Seiji Kojima; Michio Homma; Katsumi Imada

doi:10.1128/mBio.00292-19

Structure of Vibrio FliL, a New Stomatin-like Protein That Assists the Bacterial Flagellar Motor Function

mBio. 2019 Mar 19;10(2):e00292-19. doi: 10.1128/mBio.00292-19.

Authors

Norihiro Takekawa¹, Miyu Isumi¹, Hiroyuki Terashima², Shiwei Zhu^{2

3}, Yuuki Nishino², Mayuko Sakuma^{2

4}, Seiji Kojima², Michio Homma², Katsumi Imada⁵

Affiliations

¹ Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
² Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Japan.
³ Department of Microbial Pathogenesis, Yale School of Medicine, Yale University, West Haven, Connecticut, USA.
⁴ Radioisotope Research Center, Nagoya University, Nagoya, Japan.
⁵ Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan kimada@chem.sci.osaka-u.ac.jp.

Abstract

Many motile bacteria swim or swarm using a filamentous rotating organelle, the flagellum. FliL, a component protein of the flagellar motor, is known to enhance the motor performance under high-load conditions in some bacteria. Here we determined the structure of the periplasmic region of FliL (FliL_Peri) of the polar flagellum of Vibrio alginolyticus FliL_Peri shows a remarkable structural similarity to the stomatin/prohibitin/flotillin/HflK/C (SPFH) domain of stomatin family proteins, some of which are involved in modulation of ion channel activities in various organisms. FliL_Peri forms a ring assembly in the crystal with an inner diameter of around 8 nm, which is comparable to the size of the stator unit. Mutational analyses suggest that the FliL ring forms a complex with the stator unit and that the length of the periplasmic linkers of FliL and the stator B-subunit is essential for the complex formation. We propose a model of the FliL-stator complex to discuss how Vibrio FliL modulates stator function in the bacterial flagellar motor under conditions of high viscosity.IMPORTANCE Some flagellated bacteria regulate motor torque in response to the external load change. This behavior is critical for survival, but the mechanism has remained unknown. Here, we focused on a key protein, FliL of Vibrio alginolyticus, and solved the crystal structure of its periplasmic region (FliL_Peri). FliL_Peri reveals striking structural similarity to a conserved domain of stomatin, which is involved in ion channel regulation in some organisms, including mammals. FliL_Peri forms a ring with an inner diameter that is comparable in size to the stator unit. The mutational analyses suggested that the presence of the ring-like assembly of FliL around the stator unit enhances the surface swarming of Vibrio cells. Our study data also imply that the structural element for the ion channel regulation is conserved from bacteria to mammals.

Keywords: bacterial flagellar motor; crystal structure; mechanosensor; stator; stomatin.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Bacterial Proteins / chemistry*
Bacterial Proteins / genetics
Bacterial Proteins / metabolism*
Crystallography, X-Ray
DNA Mutational Analysis
Flagella / enzymology*
Flagella / physiology*
Membrane Proteins / chemistry*
Membrane Proteins / genetics
Membrane Proteins / metabolism*
Motion*
Protein Conformation
Protein Multimerization
Vibrio alginolyticus / enzymology*
Vibrio alginolyticus / physiology*

Substances

Bacterial Proteins
Membrane Proteins
FliL protein, Bacteria