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Toxins trapped in cork-fixed capsules

RhsA encapsulates its toxic effector domain (red). The cocoons are sealed with a cork structure (yellow). Cleavage inside RhsA occurs via the blue autoprotein degradation domain. Credits: Max Planck Institute of Molecular Physiology

An estimated 100 trillion bacteria inhabit the microbial flora and exist as a dense colony of various strains and species. Like all living things, bacteria must engage in a “war” by competing with each other for space and resources, releasing toxins and killing their competitors. One of the many weapons bacteria use in this inevitable battle is the Type VI Secretory System (T6SS), which delivers toxic effectors to the enemy. Stefan Raunser of the Max Planck Institute for Molecular Physiology in Dortmund and John Whitney’s group at McMaster University in Canada have together discovered the high resolution 3D structure of such effectors from Pseudomonas protegens by cryo-electron microscopy. An effector protein called RhsA contains a toxic component that is unlocked and ready to be fired in a cork-like, sealed molecular cocoon. Their findings will not only help us understand how T6SS machines work, but will also facilitate future development of antibacterial treatments and plant protection strategies.


Beneficial Bacteria Pseudomonasprotegens protects plants from fungi and bacteria. But behind this seemingly selfless act is a complex system in which bacteria try to occupy a biological niche by eliminating competitors. To this end, Bacteria has developed all poisonous weapons and various injection systems to prepare them for battle.

Like a poison dart

One of the most widely used injection mechanisms for Gram-negative bacteria is the type VI secretion system. When the machine is activated, nanotubes are assembled inside the cell and poison darts with deadly toxic proteins attached to their tips are shot into competitors. The 3D structure of the bacterial RhsA effector, one of these toxic proteins, was solved by Raunser’s team along with Whitney’s team. Scientists have discovered that RhsA effectors consist of the toxic weapon itself, the cocoons that surround it, and a cork-like plug. toxin Completely encapsulate the cocoon.

Bacterial Hidden Weapon: Toxin trapped in a cork-fixed capsule

First, seals and toxins are cleaved from the remaining proteins (scissors) and then attached to poison dart frogs. Credits: Max Planck Institute of Molecular Physiology

Unlock Bacterial Weapons

“Cocoons protect the bacteria from their self-produced toxins,” says Raunser. “We have already observed a very similar strategy for bacterial Tc toxins.” Scientists have found that the effector protein itself cleaves lizards and toxins from the remaining proteins, thereby locking the deadly weapon. It was shown to be released. However, the release of toxic components is not yet possible because the seal holds the cocoon in place. “When a poison dart frog invades an enemy bacterium, it appears to generate mechanical force to remove the cleaved seal, much like a champagne cork pops, so that the toxin is in the right place. It will be released at the right time. “

In a series of previous collaborative projects, scientists have already gained a lot of knowledge about how the T6SS injection system works. They were able to clarify how effectors are transported intracellularly, how they are loaded into toxic darts, and how darts are delivered to host cells. rice field. “Our latest collaboration provides molecular insights into the Rhs effector’s armed process and its importance to toxin release. Our ongoing collaboration reveals more details on the T6SS machine. I am very optimistic about becoming. Bacteria It has improved pathogen control functions that are useful for antibacterial and antifungal applications, “says Whitney.

The study was published in PLOS pathogen..


New insights into molecular weapons of plant microbiota


For more information:
Patrick Güntheretal, Bacterial Rhs Effector Structure Exported by Type VI Secretory System, PLOS pathogen (2022). DOI: 10.1371 / journal.ppat.1010182

Provided by
Max Planck Society

Quote: Bacterial Hidden Weapon: Toxin (February 9, 2022) trapped in a cork-fixed capsule, https: //phys.org/news/2022-02-bacteria-hidden-weapon- Obtained from toxins-capsule.html on February 9, 2022

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Toxins trapped in cork-fixed capsules

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