How bacteria adhere to fiber in the gut
Molecular mechanics of bacterial superglue

Date:
August 28, 2020
Source:
University of Basel
Summary:
Researchers have revealed a new molecular mechanism by which
bacteria adhere to cellulose fibers in the human gut. Thanks to
two different binding modes, they can withstand the shear forces
in the body.



FULL STORY ========================================================================== Researchers have revealed a new molecular mechanism by which bacteria
adhere to cellulose fibers in the human gut. Thanks to two different
binding modes, they can withstand the shear forces in the body. Scientists
of the University of Basel and ETH Zurich published their results in
the journal Nature Communications.


========================================================================== Cellulose is a major building block of plant cell walls, consisting of molecules linked together into solid fibers. For humans, cellulose is indigestible, and the majority of gut bacteria lack the enzymes required
to break down cellulose.

However, recently genetic material from the cellulose-degrading
bacterium R.

champanellensis was detected in human gut samples. Bacterial colonization
of the intestine is essential for human physiology, and understanding how
gut bacteria adhere to cellulose broadens our knowledge of the microbiome
and its relationship to human health.

The bacterium under investigation uses an intricate network of scaffold proteins and enzymes on the outer cell wall, referred to as a cellulosome network, to attach to and degrade cellulose fibers. These cellulosome
networks are held together by families of interacting proteins.

Of particular interest is the cohesin-dockerin interaction responsible
for anchoring the cellulosome network to the cell wall. This interaction
needs to withstand shear forces in the body to adhere to fiber. This
vital feature motivated the researchers to investigate in more detail
how the anchoring complex responds to mechanical forces.

By using a combination of single-molecule atomic force microscopy,
single- molecule fluorescence and molecular dynamics simulations,
Professor Michael Nash from the University of Basel and ETH Zurich along
with collaborators from LMU Munich and Auburn University studied how
the complex resists external force.

Two binding modes allow bacteria to stick to surfaces under flow They
were able to show that the complex exhibits a rare behavior called
dual binding mode, where the proteins form a complex in two distinct
ways. The researchers found that the two binding modes have very different mechanical properties, with one breaking at low forces of around 200 piconewtons and the other exhibiting a much higher stability breaking
only at 600 piconewtons of force.

Further analysis showed that the protein complex displays a behavior
called a "catch bond," meaning that the protein interaction becomes
stronger as force is ramped up. The dynamics of this interaction are
believed to allow the bacteria to adhere to cellulose under shear stress
and release the complex in response to new substrates or to explore
new environments.

"We clearly observe the dual binding modes, but can only speculate
on their biological significance. We think the bacteria might control
the binding mode preference by modifying the proteins. This would allow switching from a low to high adhesion state depending on the environment," Professor Nash explains.

By shedding light on this natural adhesion mechanism, these findings set
the stage for the development of artificial molecular mechanisms that
exhibit similar behavior but bind to disease targets. Such materials
could have applications in bio-based medical superglues or shear-enhanced binding of therapeutic nanoparticles inside the body. "For now, we are
excited to return to the laboratory and see what sticks," says Nash.


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


========================================================================== Journal Reference:
1. Zhaowei Liu, Haipei Liu, Andre's M. Vera, Rafael C. Bernardi, Philip
Tinnefeld, Michael A. Nash. High force catch bond mechanism of
bacterial adhesion in the human gut. Nature Communications, 2020;
11 (1) DOI: 10.1038/s41467-020-18063-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200828115357.htm

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