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Bacteria have established various strategies to infect organisms and use them as sources of nutrients. Many microbes use toxins that break down membranes by simply piercing through the outer shell of the cells. Human-pathogenic bacteria such as the plague bacterium Yersinia pestis or other bacteria from the salmonella family developed a much more subtle mechanism: they inject their poison by applying a special toxin complex. A team of researchers led by Stefan Raunser from the Max Planck Institute of Molecular Physiology in Dortmund has now been able to fully unveil the sophisticated mechanism using the bacterium Photorhabdus luminescens as an example.
Bacterial toxins are among the most effective natural poisons. The strongest toxins include e.g. the tetanus and botulinum toxins (botox), already toxic when only a thousandth of a gram is administered. Bacteria have developed highly varied strategies and mechanisms to introduce their poisons into organisms. The bacterium Photorhabdus luminescens, the plague bacterium Yersinia pestis, as well as germs from the salmonella family, use so-called Tc toxins which consist of several components (TcA, TcB, TcC). Until recently, it was unclear how these subunits work together.
Cases - Bio-molecules - Bacterial - Toxins - Crystallography
In most cases, large bio-molecules such as the complex bacterial toxins cannot be structurally analysed using traditional X-ray crystallography, because they cannot be converted into the required crystalline state. Cryo-electron microscopy, however, does not require the samples to be crystallized. Imaging of even large complexes becomes possible, by freezing them extremely quickly and examining them directly under the microscope at minus 196 degrees. Using cryo-EM the team of Stefan Raunser was able to determine the three-dimensional structure of the Photorhabdus luminescens toxin for the first time in near-atomic detail. The structures showed, that the largest subunit of the poison complex, TcA, resembles a bell, consisting of a channel surrounded by a shell. The upper part of the...
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