News in 2021
New Publication in Nature
An Arabidopsis regulatory module controlling pathogen resistance triggered by cell-surface and intracellular receptors
Collaborative research led by the group of Thorsten Nürnberger at ZMBP (University of Tübingen) and Jane Parker (Dept. Plant-Microbe Interactions at MPIPZ Cologne) with colleagues at ZMBP and MPIPZ has identified a convergence point for defence signalling triggered by plant cell-surface (microbial pattern recognition) and intracellular (pathogen effector recognition) immune receptors. These two receptor systems use a regulatory node consisting of three proteins: EDS1, PAD4 and ADR1 to mobilize anti-pathogen defence pathways. The new findings provide an excellent lead to how and where inside host cells cell-surface and intracellular pathogen detection systems intersect to confer strong disease resistance.
Upon ligand perception, Arabidopsis cell-surface RLK pattern-recognition receptors interact with BAK1 to activate pattern-triggered immunity (PTI). RLKs have a partial requirement for the EDS1‑PAD4‑ADR1 node (grey dashed arrow). PTI conferred by PRR RLP23, following dimerization with RLKs BAK1 and SOBIR1, signals primarily through EDS1-PAD4-ADR1. Together with an important cytoplasmic kinase (PBL31), EDS1, PAD4 and ADR1 can be detected in close proximity to an SOBIR1/RLP23 complex at the plasma membrane before and after RLP23 elicitation, suggesting presence of pre-formed complexes ready for downstream signalling. Some RLP-triggered defences do not require EDS1-PAD4-ADR1 (black dashed arrow). Effector-triggered immunity (ETI) conferred by NLR receptors uses EDS1-PAD4-ADR1 and/or a related node consisting of EDS1-SAG101 and NRG1 (green arrows). This model further erodes a previously held strict distinction between PTI and ETI, and supports the concept that surveillance systems for pathogen disturbance outside and inside plant cells use overlapping machineries for disease resistance.
(MAMPs: Microbe associated molecular patterns; RLK: Receptor-like kinase; RLP: Receptor-like protein; BAK1: BRI1-associated receptor kinase; SOBIR1: Suppressor of BIR1 1; PBL31: PBS1-like 31; EDS1: Enhanced disease susceptibility 1; PAD4: Phytoalexin deficient 4; SAG101: Senescence-associated gene 101; NLR: Nucleotide-binding leucine-rich repeat; NRG1: N requirement gene 1; ADR1:Activate disease resistance 1; PTI: Pattern triggered immunity; ETI: Effector triggered immunity).
3 Projects of SFB 1403 Junior Scientists were funded
The SFB 1403 promotes interactions between plant an animal cell death research with tandem grants for small research projects with at scientists from both fields. The tandem grants fund new reach ides with proof of principle experiments in the field of cell death.
We are happy to announce that 3 Project were funded in 2021. Congratulations to:
- "Substrates of the potential Shigella effector protease NleC: Searching for conserved targets in mammal and plant immune pathways" by Dr. Sina Barghahn (Döhlemann Lab), Dr. Melanie Fritsch (Kashkar Lab), and Melissa Mantz (Huesgen Lab)
- "Definition of microscopic hallmarks of the Programmed Cell Death in plants" by Anna Kostina (Garcia-Saez lab)
- "The Role of RBOH and SO-dependent ROS production in Serendipita indica fungal-induced cell death phase during endophytic colonization of Arabidopsis roots" by Patricia Zecua and Besarta Thaqi
New Publication in Science
An international research team led by the University of Bonn has identified and further developed novel antibody fragments against the SARS coronavirus-2. These "nanobodies" are much smaller than the classic antibodies used to treat US President Donald Trump, for example. They therefore penetrate the tissue better and can be produced more easily in larger quantities. The researchers at the University Hospital Bonn have also combined the nanobodies into potentially particularly effective molecules. These attack different parts of the virus simultaneously. The approach could prevent the pathogen from evading the active agent through mutations. The results are published in the journal Science.
Antibodies are an important weapon in the immune system's defense against infections. They bind to the surface structures of bacteria or viruses and prevent their replication. One strategy in the fight against disease is therefore to produce effective antibodies in large quantities and inject them into the patients. The outgoing US President Donald Trump probably owes his rapid recovery to this method. However, the antibodies used to treat him have a complex structure, do not penetrate very deeply into the tissue and may cause unwanted complications. Moreover, producing antibodies is difficult and time-consuming. They are therefore probably not suitable for widespread use.
Mass production in yeast or bacteria
"We focus on another group of molecules, the nanobodies," explains Dr. Florian Schmidt, who heads an Emmy Noether group on this promising new field of research at the University of Bonn's Institute of Innate Immunity. "Nanobodies are antibody fragments that are so simple that they can be produced by bacteria or yeast, which is less expensive."
However, the immune system produces an almost infinite number of different antibodies, and they all recognize different target structures. Only very few of them are for example capable of defeating the SARS coronavirus-2. Finding these antibodies is like searching for a single grain of sand on Germany's Baltic coast. "We first injected a surface protein of the coronavirus into an alpaca and a llama," Schmidt explains. "Their immune system then produces mainly antibodies directed against this virus. In addition to complex normal antibodies, llamas and alpacas also produce a simpler antibody variant that can serve as the basis for nanobodies."
A few weeks later, the researchers took a blood sample from the animals, from which they extracted the genetic information of produced antibodies. This "library" still contained millions of different construction plans. In a complex process, they extracted those that recognize an important structure on the surface of the coronavirus, the spike protein. "Altogether we obtained dozens of nanobodies, which we then analyzed further," explains Dr. Paul-Albert König, head of the Core Facility Nanobodies at the Medical Faculty of the University of Bonn and lead author of the study.
Four out of several million
Four molecules actually proved to be effective against the pathogen in cell cultures. "Using X-ray structures and electron microscopy analyses, we were furthermore able to show how they interact with the spike protein of the virus," explains König. This work was done in the research groups around Martin Hällberg (Karolinska Institutet, Sweden) and Nicholas Wu as well as Ian Wilson (Scripps Research Institute, USA). The spike protein is crucial for the infection: It acts like a velcro fastener with which the pathogen attaches to the attacked cell. Next, the velcro changes its structure: It discards the component that is important for attachment and mediates fusion of the virus envelope with the cell. "Nanobodies also appear to trigger this structural change before the virus encounters its target cell - an unexpected and novel mode of action," says König. "The change is likely to be irreversible; the virus is therefore no longer able to bind to host cells and infect them."
The researchers also exploit another major advantage of nanobodies over antibodies: Their simple structure allows straight forward combinations to form molecules that can be several hundred times more effective. "We have fused two nanobodies that target different parts of the spike protein," explains König. "This variant was highly effective in cell culture. Furthermore, we were able to show that this drastically reduces the probability of the virus to become resistant to the active agent through escape mutations." The researchers are convinced that the molecules may be developed into a novel and promising therapeutic option.
Dioscure Therapeutics, a spin-off of the University of Bonn, will test the nanobodies in clinical studies. The success of the project is mainly based on the excellent cooperation of the participating research groups at the University with national and international cooperation partners, emphasizes Florian Schmidt, who is also a member of the Immunosensation2 Cluster of Excellence at the University of Bonn.
Institutions from Germany, Sweden and the USA were involved in the study. Diffraction data were collected at Stanford Synchrotron Radiation Lightsource (SSRL) and at the Advanced Photon Source (APS) at Argonne National Labs in the USA.
In Germany, the study was financially supported by the Medical Faculty of the University of Bonn, the German Research Foundation, the Klaus Tschira Boost Funds, the Federal Ministry of Education and Research, the Baden-Württemberg Foundation and the MWK Baden-Württemberg. In the USA, the Bill and Melinda Gates Foundation, the U.S. Department of Energy, the National Institutes of Health (NIH), the National Institute of General Medical Sciences (NIGMS) and the National Cancer Institute (NCI) funded the project, in Sweden the Swedish Research Council and the Knut and Alice Wallenberg Foundation.
The founders of the company Dioscure were supported by the enaCom Transfer Center at the University of Bonn providing a link between research and industry with its offers. As University of Bonn's IP Service Provider, PROvendis GmbH negotiates the commercialization contract with Dioscure.
News in 2020
New Publication in Cell Host & Microbe
For plant and animal immune systems the similarities go beyond sensing
University of Cologne and SFB 1403 researcher Takaki Maekawa and colleagues have discovered that plants have independently evolved a family of immune proteins that are strikingly similar to animals.
Although profoundly different in terms of physiology, habitat and nutritional needs, plants and animals are confronted with one shared existential problem: how to keep themselves safe in the face of constant exposure to harmful microorganisms. Mounting evidence suggests that plants and animals have independently evolved similar receptors that sense pathogen molecules and set in motion appropriate innate immune responses. Now, in a study just published in the journal Cell Host & Microbe, senior author Takaki Maekawa together with co-first authors Lisa K. Mahdi, Menghang Huang, Xiaoxiao Zhang and colleagues have discovered that plants have evolved a family of proteins that bear a striking resemblance to proteins called mixed lineage kinase domain-like proteins (MLKLs), which trigger cell death in vertebrates as part of the immune response. In uncovering and characterizing an important new family of plant immune proteins, the authors’ study, which involved collaboration with fellow SFB 1403 researchers Paul Schulze-Lefert, Jane Parker and Jijie Chai, provides intriguing new insights into how plants protect themselves from microbial invaders.
Regulated cell death often accompanies immunity against infection in plants, animals and fungi. One pervasive theory suggests that highly localised cell death responses serve to strictly limit the spread of infection. Although starting from independent origins this shared response seems to also involve highly similar machinery: many proteins involved in cell death in different kingdoms of life contain a so-called HeLo domain, a bundle structure made up of four helices, which causes resistance and cell death by disturbing the integrity of cellular membranes or forming ion channels.
Based on the similarities between animal and plant immune systems and on the key role played by HeLo domains in cell death, Maekawa hypothesised that plants might also contain other proteins with HeLo domains. Making use of bioinformatic and structural analysis, he and his team discovered a new family of HeLo domain-containing proteins that are widely shared among different plant species, indicating that they are important for plant physiology.
Maekawa termed the proteins plant MLKLs, and for further studies he focused on MLKLs expressed in the model plant Arabidopsis thaliana. He and his team isolated MLKL proteins from A. thaliana and determined that plant MLKLs possess the same overall protein architecture as their vertebrate counterparts and also assemble into tetramer, likely auto-inhibited, structures when they’re not active. Importantly, plant MLKLs also play a role in immunity, as plants in which genes encoding these proteins were mutated and thus non-functional were susceptible to pathogen infection.
Further investigation revealed additional similarities with vertebrate MLKLs: plant MLKLs are also trafficked to cellular membranes as part of their function, and activation of these proteins leads to cell death. Maekawa now aims to discover the molecular details underlying the function of plant MLKLs in immunity: “It will be exciting to uncover exactly how MLKLs are activated upon pathogen infection and how this activation is translated into effective plant protection.”
Helga Freyberg-Rüßman-Award for Melanie Fritsch
During her PhD in the lab of Hamid Kashkar, Melanie Fritsch was working on the role of caspase-8 in the regulation of different mechanisms of cell death and their impact on the development of systemic inflammation. For her work she received the Helga Freyberg-Rüßman-Award. The Helga Freyberg-Rüßman-Prize is awarded to outstanding scientific achievements to young scientists by the "Kölner Gymnasial- und Stiftungsfonds" in cooperation with the medical faculty of the University of Cologne.
Congratulations to Melanie Fritsch!
For more information see: https://www.facebook.com/Stiftungsfonds/
SFB 1403 started in 2020
The SFB 1403 focuses on cell death and its role in immunity and disease. Cell death is a fundamental biological process for multicellular organisms, traditionally viewed as a process safeguarding tissue homeostasis by counterbalancing cell proliferation. This view has dramatically changed during the last years by the identification of different genetically controlled cellular death programs and the realisation that these cell death pathways contribute to immunity and disease. Accumulating evidence revealed that dying cells communicate with bystander cells triggering tissue responses that could be protective by mediating tissue repair but could also cause tissue damage and disease. A new concept has now emerged, in which cell death is an integral component of the organismal response to stress caused by microbial and non-microbial insults that is important for both protective immunity and the pathogenesis of immune-related diseases. The overarching goal of the CRC 1403 is to explore how diverse forms of cell death are regulated and how they contribute to health and disease in animals and plants, with particular focus on immunity, inflammation and host-microbe interactions. The CRC1403 includes projects from scientists from the MNF and the Medical faculty of the UoC, together with scientists from the MPI for Plant Breeding Research and the MPI for Ageing Research and groups from the University of Bonn and the LMU in Munich. The CRC also provides a link between the Excellence Clusters CECAD and CEPLAS in Cologne as well as the EC Immunosensation in Bonn.