3D model shows bacterial motor in action

Date:
November 9, 2020
Source:
Nagoya University
Summary:
Scientists have constructed a high-resolution 3D model that shows
what happens when a bacterial motor switches directions.



FULL STORY ========================================================================== Nagoya University scientists in Japan and colleagues at Yale University
in the US have uncovered details of how the bacterial propeller, known as
the flagellum, switches between counterclockwise and clockwise rotation, allowing it to control its movement. The findings were published in the
journal eLife and include a model that shows structural changes happening within portions of the flagellar motor.


========================================================================== Vibrio bacteria are rod-shaped organisms that live in coastal waters. They
can cause serious intestinal and soft tissue infections that can
ultimately lead to septic shock and multiple organ failure. "Vibrio
infections are expected to increase as water temperatures rise due to
climate change," says Nagoya University supramolecular biologist Michio
Homma. "They have evolved a sophisticated flagellum-driven motility to facilitate their invasion of host organisms. We wanted to visualize how
their motors switch between clockwise and counterclockwise rotation to
further understand this movement." To do this, Homma and his colleagues
used an advanced imaging technique called cryo-electron tomography, in
which images are taken of frozen samples as they are tilted to produce 2D images that are combined to produce a 3D reconstruction. The scientists
used samples from two mutant Vibrio bacteria whose flagella only rotated
in the clockwise or counterclockwise direction.

This allowed them to compare the two movements and deduce the changes
happening within the bacteria's motor to switch directions.

"Our comparative analysis and molecular modelling provide the first
structural evidence that the flagellar motor undergoes a profound
rearrangement to enable the rotational switch," says Homma.

The scientists found that the switch from counterclockwise to clockwise involves a signalling protein, called CheY-P, binding to a protein,
called FliM, in the flagellar motor's C-ring. This causes another motor protein, called FliG, to move in a way that exposes charged residues
on its surface to a transmembrane protein, called PomA, that forms the stationary part of the motor, called the stator, along with another
protein called PomB. The interaction between FliG residues and PomA
probably leads to changes in the stator that result in an ion flow
generating torque, which ultimately rotates the C-ring.

"Cryo-electron tomography is rapidly evolving, making it increasingly
possible to reveal motor structure at higher resolutions," says
Homma. "This current study provides one of the highest resolution images
by cryo-electron tomography of the Vibrio flagellar motor. This and
future studies will further our understandings of the flagellar assembly
and function."

========================================================================== Story Source: Materials provided by Nagoya_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Brittany L Carroll, Tatsuro Nishikino, Wangbiao Guo, Shiwei Zhu,
Seiji
Kojima, Michio Homma, Jun Liu. The flagellar motor of Vibrio
alginolyticus undergoes major structural remodeling during
rotational switching. eLife, 2020; 9 DOI: 10.7554/eLife.61446 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/11/201109132441.htm

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