A bacterial toxin turning cells into swiss cheese

June 23, 2020

Kanazawa, Japan - Although the innate immune system is the front line of defense against microbial infections, the complex mechanisms of innate immunity are incompletely understood. In a new study, researchers from Kanazawa University synthesized and characterized the bacterial toxin Monalysin to enable the study of how the innate immune system and toxin-producing bacteria interact with each other.

The innate immune system detects microbial infections through sensing either microbial molecules (pathogen-associated molecular patterns, or PAMPs) or host signaling molecules that are released from damaged host cells (damage-associated molecular patterns, or DAMPs). The bacterium Pseudomonas entomophila has been utilized as a tool to study the mechanisms of DAMPs in the gut. P. entomophila infects insects and damages intestinal cells using a pore-forming toxin called Monalysin. Monalysin is secreted as an inactive pro-toxin, which is then activated by certain proteins called proteases. Although the fruit fly, Drosophila, protects itself from activation of the pro-toxin by building a physical barrier against proteases, it can still take damage upon exposure to the toxin.

"Activated Monalysin forms pores in the plasma membrane of host cells, resulting in cell death, so it is important for the host to prevent its activation," says corresponding author of the study Takayuki Kuraishi. "We wanted to purify and functionally characterize Monalysin from P. entomophila to develop a tool that could help us understand how the host and bacteria that produce pore-forming toxins interact."

To achieve their goal, the researchers cultured P. entomophila and purified pro-Monalysin from their lysates. By reacting the purified toxin with Drosophila cells, the researchers confirmed its toxic effect when cell viability dropped significantly as more pro-Monalysin was added to the cells. To confirm that purified Monalysin forms pores, the researchers added activated Monalysin onto a chip covered with a lipid bilayer, similar to the plasma membrane of cells. By measuring the electrical current resulting from ion passage through the formed pores, the researchers showed that Monalysin forms pores around 0.7-1nm in diameter. To analyze the structural composition of Monalysin, the researchers then turned to atomic force microscopy (AFM), which provides high-resolution images by touching the surface with a sensitive mechanical probe. Using AFM, the researchers showed that eight Monalysin molecules came together to form pores in the plasma membrane. By combining AFM with high-speed imaging, the researchers then demonstrated that activated Monalysin preferentially inserted into the edge of the plasma membrane, suggesting that highly curved parts of membranes are the sites of their action.

"These are striking results that show how Monalysin functions at the molecular level," says Kuraishi. "Our findings could help understand how the innate immune system fights off bacteria that produce pore-forming toxins."
-end-


Kanazawa University

Related Plasma Membrane Articles from Brightsurf:

Lighting the way to selective membrane imaging
A team of scientists at Kanazawa University have shown how water-soluble tetraphenylethene molecules can become fluorescent when aggregating at a biomembrane-mimetic liquid-liquid interface.

What membrane can do in dealing with radiation
USTC recently found that polymethylmethacrylate (PMMA) and polyvinyl chloride (PVC) can release acidic substance under γ radiation, whose amount is proportional to the radiation intensity.

Using light's properties to indirectly see inside a cell membrane
Using properties of light from fluorescent probes is at the heart of a new imaging technique developed at Washington University's McKelvey School of Engineering that allows for an unprecedented look inside cell membranes.

Cells relax their membrane to control protein sorting
The tension in the membrane of cells plays an important role in a number of biological processes.

Across the cell membrane
Aquaporins and glucose transporters facilitate the movement of substances across biological membranes and are present in all kingdoms of life.

First simulation of a full-sized mitochondrial membrane
Scientists from the University of Groningen have developed a method that combines different resolution levels in a computer simulation of biological membranes.

New self-forming membrane to protect our environment
A new class of self-forming membrane has been developed by researchers from Newcastle University, UK.

Cell membrane proteins imaged in 3D
A team of scientists including researchers at the National Synchrotron Light Source II have demonstrated a new technique for imaging proteins in 3D with nanoscale resolution.

Quantum-entangled light from a vibrating membrane
Researchers from the Quantum Optomechanics group at the Niels Bohr Institute, University of Copenhagen, recently entangled two laser beams through bouncing them off the same mechanical resonator, a tensioned membrane.

Visualizing molecular patterns of membrane TNF receptors
Whether a sick cell dies, divides, or travels through the body is regulated by a sophisticat-ed interplay of signal molecules and receptors on the cell membrane.

Read More: Plasma Membrane News and Plasma Membrane Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.