First structure of human protein complex with ‘licence to kill’

First structure of human protein complex with ‘licence to kill’

A team of WEHI researchers has for the first time visualised a human cell death complex linked to autoimmune and inflammatory conditions, such as inflammatory bowel disease, and injuries associated with excessive cell death.

Using the Australian Synchrotron, the team solved the structure of the human cell death proteins MLKL and RIPK3 bound to each other, as well as human RIPK3 alone. When RIPK3 activates MLKL, it triggers a type of inflammatory cell death called necroptosis that kills the cell and alerts the immune system that it is under attack. However, when uncontrolled, necroptosis has been linked to human inflammatory diseases.

The findings will help scientists discover drugs that can target and suppress cell death by necroptosis, which could lead to new treatments for a range of autoimmune and inflammatory diseases including inflammatory bowel disease, renal injury and diabetes.

The research, published in Nature Communications, was led by WEHI researchers Yanxiang Meng, Dr Katherine Davies, Associate Professor Peter Czabotar and Associate Professor James Murphy. The discovery is the latest in an almost 15-year-long journey to understand necroptosis for treating disease.

At a glance

‘The cell death pathway’

Necroptosis is a type of inflammatory cell death process that helps protect the body against infection. Most often triggered when a cell is infected by a virus or bacteria, the cell is instructed to die and send inflammatory signals to warn the immune system of foreign invaders. However, when necroptosis is uncontrolled or excessive, the inflammatory response can trigger disease.

PhD student Yanxiang Meng said that MLKL and RIPK3 are bound in an inert state in all cells of the body, waiting to be activated.

“MLKL and RIPK3 form an inert complex, with RIPK3 ‘holding’ MLKL in an inactive state to prevent necroptotic cell death,” he said.

“When the cell is infected, RIPK3 chemically modifies MLKL then detaches, giving it a ‘licence to kill’ the infected or damaged cell for the greater good,” he said.

He said the Australian Synchrotron and Collaborative Crystallisation Centre (C3) facility at CSIRO were crucial to visualise the structure of human forms of RIPK3 bound to human MLKL for the first time.

“The necroptotic cell death proteins are conserved across different organisms, however there are differences between the proteins’ structures in different animals and how they bind to each other.

“We showed that the human versions of these proteins bind differently to what we have seen in other species. This is something the scientific community has been waiting many years for.”

New targets for drug discovery

Dr Davies said the team hoped this structural information would, in the future, lead to new treatment options for patients suffering from diseases linked to excessive necroptosis. 

“We now have a picture of how two key proteins in this death pathway are maintained in their dormant state. It would be interesting to know how this is regulated and leads to disease and whether this could be targeted with small molecule drugs,” she said.

The research was supported by ACRF, Australian Government National Health and Medical Research Council and Department of Education, Skills and Employment, Australian Institute of Nuclear Science and Engineering (AINSE) Postgraduate Research Award, Melbourne Research Scholarship, Wendy Dowsett Scholarship, and the Victorian Government. 

Original source here.

COVID-19 vaccine and IBD

Patients with inflammatory bowel disease (IBD) are frequently treated with immunosuppressive medications.

By Associate Professor Britt Christensen 

Key Messages

Prior to COVID-19 vaccine access, most recommendations and publications reported on preventing COVID-19 infection in immunocompromised patients by encouraging social exclusion. 

It was evident early in the pandemic that immune-compromised patients would be faced with additional concerns and consequences regarding both infection with SARS-CoV-2 and vaccination against COVID-19. It has therefore become a priority of my research activities to help address these concerns. 

As a researcher at the University of Melbourne and The Royal Melbourne Hospital, I lead a team of clinician scientists looking at multiple facets of IBD including the pathogenesis of IBD, monitoring and optimisation techniques and the development of new treatment strategies. 

Our team realised early on that there was a need for ongoing, updated information around SARS-CoV-2 infection and prevention in immunocompromised individuals for both patients and clinicians. This led to our review article published in Alimentary Pharmacology and Therapeutics early last year summarising the issues around prevention, diagnosis and management of COVID-19 infection in patients with IBD and highlighted that patients with IBD were unlikely to be at increased risk of being infected with SARS-CoV-2 or developing serious COVID-19. 

The exception to this was patients on high dose corticosteroids who may be more likely to develop serious complications from COVID-19. We therefore recommended that patients stay on maintenance medical therapy with the aim to reduce flares, prevent the need for corticosteroids and prevent inpatient admission where patients may be more likely to be exposed. These conclusions have since been confirmed in prospective studies around the world. Our research group published a further review article on COVID-19 vaccination and IBD which highlighted that COVID-19 vaccination is safe in IBD patients and is recommended early. We also concluded that high dose corticosteroids may reduce the immune response to COVID-19 vaccination and therefore in areas of low community transmission, it may be prudent to withhold vaccination in patients on high dose corticosteroids until they are on equivalent doses of prednisolone <20mg per day. 

Undergoing the process of this vaccine review highlighted to our team the knowledge gap regarding immune responses to COVID-19 vaccination in patients with autoimmune conditions on a range of immunosuppressive medications.

Remarkably, within 18 months of the beginning of the pandemic, nine COVID-19 vaccines worldwide have been approved. However, clinical trials for these vaccines have excluded patients who are immunocompromised or been exposed to immunosuppressive medications within 3-6 months of vaccine administration. Therefore, the efficacy and safety of COVID-19 vaccines in these patient cohorts remains to be determined. 

This led our research team to Professor Katherine Kedzierska’s incredible lab at The Doherty Institute. Together with my fellow Eva Zhang, Dr Katherine Bond Head of Microbiology at The Royal Melbourne Hospital and Oahn Nguyen an NHRMC Fellow at The Doherty Institute, we have set up the exciting collaborative research study, Immune Responses to COVID-19 Vaccination in Immunocompromised Hosts (IRVAX).

This single site prospective observational cohort study aims to characterise the immune responses to COVID-19 vaccines in patients with autoimmune conditions including inflammatory bowel disease, rheumatological and dermatological diseases who are taking immunosuppressant medications including biological agents. 

107 patients have been recruited and serial blood tests before and after their first, second and, where applicable, third (both primary and booster) COVID-19 vaccine are being collected. We are analysing antibody and T cell response at these various time-points and differences in the immune response in this immunosuppressed group will be compared to healthy controls. We will also evaluate immune responses stratified by immunosuppressive medication regimen, autoimmune condition and type of vaccine received. 

This study will be one of the first to characterise the T cell response in addition to B cell response to COVID-19 vaccination in patients with autoimmune conditions on a range of immunosuppressants. It will also be the first study to describe the immune response to third dose primary vaccination and booster vaccination in an immunocompromised cohort with autoimmune diseases and one of the first to be able to compare these results to healthy controls. This study will allow us to accurately determine whether and to what degree immunosuppressive medications have an impact on the immune response to vaccination. This will be practice changing and provide the evidence required to develop accurate guidelines regarding vaccine timing, dosing and protection in this vulnerable group. 


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