A new molecular mechanism by which bacteria adhere to cellulose fibers in the human gut has been identified. The team—comprised of scientists of the University of Basel and ETH Zurich—published their results in Nature Communications.
Through single-molecule atomic force microscopy, single-molecule fluorescence, and molecular dynamics simulations, the team showed how the anchoring complex resists external force. The team focused on the cohesin-dockerin interaction, which is responsible for anchoring the cellulosome network to the cell wall.
They were able to demonstrate that the complex exhibits a dual binding mode, where the proteins form the adhesion in two distinct ways. They observed that the binding modes have different mechanical properties—one breaks at low forces of around 200 piconewtons and the other exhibits much higher stability breaking only at 600 piconewtons of force.
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Further investigation showed that the protein complex displays a behavior called a "catch bond," through which the protein interaction becomes stronger as force is ramped up. These dynamics 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," co-author Michael Nash explains.