Edible oyster mushrooms have an intriguing secret: they eat spiders and roundworms. And they do so using proteins that can punch their way into cells, leaving tidy but deadly holes. It's a trick that our immune cells also use to protect us, destroying infected cells, cancerous cells, and bacteria.
Research publishing January 27th in the open access journal PLOS Biology by an international team, led by the ARC Imaging Centre at Monash University in Melbourne and Birkbeck College in London, reveals the molecular process behind the punch. Using synchrotron light and cryo-electron microscopy, they've visualised the action of a protein called pleurotolysin - opening the way to new drug targets and new tools for medicine, agriculture, genetic engineering and nano-engineering. By taking molecular snapshots, which they've turned into a movie, the team have been able to observe the hole-punching protein as it latches onto, and puts a hole in the target cell - either killing the cell directly or providing a passage for other proteins that can kill it.
"I never believed I'd be able to see these proteins in action," says the paper's lead author Dr Michelle Dunstone. "It's an amazing mechanism, and also amazing that we now have the technology to see these hole-punching proteins at work."
Using a combination of molecular imaging, along with biophysical and computational experiments, the team have been able to show the way the pleurotolysin protein moves, unfolding and refolding to punch the hole in the target cell. And in doing so, they've also found its Achilles heel. So now they can look at how to block the hole punching mechanism, or introduce it to new places where this function is desirable.
"The next step is to take what we've learned from the oyster mushroom proteins and compare them with equivalent proteins across nature," says Michelle. "We're particularly interested in this family of proteins in humans, especially perforin, which we believe will behave in the same way."
There are potential applications in medicine: dampening immune responses in people with autoimmune disease; stopping listeria escaping our immune cells; and preventing malaria from infecting the liver. In agriculture these proteins could be introduced into plants and crops, helping them to fight off attacks from pests, and reducing the need for pesticides.
"These results are the culmination of over seven years work by from researchers on opposite sides of the world, including thousands of hours by our first authors Natalya Lukoyanova and Stephanie Kondos," says Michelle.
"We still have a lot of work to do before our ideas reach the clinic or industry but seeing how the machinery works is an important step forward," says Birkbeck College's Professor Helen Saibil, co-lead author on the paper.
For images and a movie related to this release see: http://www.
Caption explaining the movie in the above link:
The surface of the cell is shown by the double horizontal gray envelope across at the bottom. The pleurotolysin protein changes its shape, with the red section punching through the cell surface. This intricate machine is just one of 13 identical copies in a ring shape that self-assemble into a giant tunnel that breaches the cell membrane.
Dr. Michelle Dunstone
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Professor Helen Saibil
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Lukoyanova N, Kondos SC, Farabella I, Law RHP, Reboul CF, Caradoc-Davies TT, et al. (2015) Conformational Changes during Pore Formation by the Perforin-Related Protein Pleurotolysin. PLoS Biol 13(2): e1002049. doi:10.1371/journal.pbio.1002049
HRS acknowledges support from the Wellcome Trust (grant 079605/2/06/2) for EM facilities and doctoral training support to KO (MRCG1001602), the BBSRC (BB/D00873/1) and the ERC (294408). MT acknowledges the BBSRC (BB/K01692X/1) and Leverhulme Trust (RPG-2012-519). We thank D. Houldershaw and R. Westlake for computing support, L. Wang for EM support, and E.V.
Orlova, D.K. Clare and A.P. Pandurangan for discussion. MAD is a National Health and Medical
Research Council of Australia (NHMRC) Career Development Fellow. MAD acknowledges support from the Australian Research Council (ARC) [DP120104058, DP0986811, CE140100011] and the
National Health and Medical Research Council . JCW is an NHMRC Senior Principal Research Fellow. JCW also acknowledges the support of an Australian Research Council Federation Fellowship. CFR is supported by the Australian Postgraduate Award. DTacknowledges the support of an ARC Super Science Fellowship. RKT acknowledges the National Institutes of Health, NIAID [AI037657]. The authors acknowledge the support of the Victorian Life Sciences Computation Initiative (VLSCI, Melbourne, Australia) and the Multi-modal Australian ScienceS Imaging and Visualisation Environment (MASSIVE) (http://www.
The authors have declared that no competing interests exist.