Press releases

FRANKFURT. Misfolded proteins cause many diseases including neurodegenerative conditions and cancer. To protect themselves from protein misfolding, cells have developed sophisticated quality control mechanisms. How these function in the case of protein misfolding in mitochondria is now the subject of research currently being conducted by Dr. Christian Münch at the Institute of Biochemistry II of Goethe University Frankfurt. The German Research Foundation is supporting his work with an Emmy Noether grant of up to € 2 million.

The misfolding of single or several cellular proteins is a constant danger. Even just a slight rise in body temperature is sufficient to disrupt the folding balance in cells. If this occurs in mitochondria, the cell’s usual control mechanisms do not come into action because the small organelles, also known as the cell’s “powerhouses”, are separated from the rest of the cell by two membranes. They therefore need their own control mechanisms to safeguard mitochondrial protein folding.

That is why mitochondria, when their proteins fail to fold correctly, activate a stress response which attempts to correct this folding. By activating certain genes in the cell nucleus, they induce the production of proteins that support folding in the mitochondria. “Especially in the case of mammalian cells, little is known about how information about misfolded mitochondrial proteins is relayed to the cell nucleus,” explains Dr. Christian Münch.  

The research group, which Münch is currently building up with the help of the funds approved by the German Research Foundation, aims also to investigate how the stress response acts under chronic conditions and how programmed cell death is triggered if protein folding cannot be reinstated. The researchers hope in this way to discover which role these processes play in diseases and whether they can be modified for therapeutic purposes.

Dr. Münch studied biochemistry in Tübingen and Munich and completed his doctoral degree at Cambridge University, England, in 2011. He then spent several years as a researcher at Harvard Medical School in the USA. He has been a group leader at the Institute of Biochemistry II of the Faculty of Medical Science at Goethe University Frankfurt since December 2016.

In the framework of the Emmy Noether Programme, the German Research Foundation sponsors outstanding junior researchers so that they can lead their own independent junior research group and qualify for a university teaching career. The programme also especially endeavours to recruit excellent early career researchers back from abroad.

A photograph of Christian Münch can be downloaded under: www.uni-frankfurt.de/69177152 (Photo: Uwe Dettmar)

Further information: Dr. Christian Münch, Institute of Biochemistry II, Faculty of Medical Science, Niederrad Campus, Tel.: +49(0)69-6301-6599, ch.muench@em.uni-frankfurt.de.

FRANKFURT. Social media have become an indispensable part of our everyday life. We use them constantly to screen the latest news and share pre-selected information. The cells in our body do a similar thing. Information is pre-selected and transmitted to the immune system in order to fight against unwelcome invaders, such as viruses, bacteria, parasites or cancer. This pre-selection occurs by means of a highly complex molecular machine. Biochemists at Goethe University Frankfurt and the Max Planck Institute of Biophysics, in cooperation with researchers at Martin Luther University Halle-Wittenberg, have now unveiled the inner workings of this complex molecular machine.

Status updates of each cell are transmitted from the cell’s interior to the immune system in the form of small protein fragments. These fragments are presented on the cell surface by specific proteins, known as MHC-I molecules. Cancerous or infected cells can thus be quickly identified and eliminated. However, viruses and tumours can also trick the immune system and in so doing escape immune surveillance. In addition, ambiguous messages can lead to autoimmune diseases or chronic inflammation.

That is why it is particularly important to understand how this highly complex molecular machine in the cell’s interior selects the relevant protein fragments and coordinates the loading of MHC-I molecules. In the current issue of the renowned scientific journal NATURE, the researchers from Frankfurt and Halle provide first insights into the molecular architecture and inner workings of what is referred to as the MHC-I peptide-loading complex.

“We had to pull out all the stops to prepare this extremely fragile complex for structural analyses,” explains Dr. Simon Trowitzsch of the Institute of Biochemistry at Goethe University Frankfurt. “First of all, we expanded our biochemical toolbox and developed a viral molecular bait that allowed us to isolate the native MHC-I peptide-loading complex from the endoplasmic reticulum.”

“Thanks to groundbreaking advances in cryo-electron microscopy, which were recently awarded the Nobel Prize, we were able to look closely at the MHC-I peptide-loading complex - which is about a hundred thousand times smaller than a pinhead - and to determine its molecular structure,” reports Dr. Arne Möller from the Max Planck Institute of Biophysics.

The scientists can now deduce how the cell manages to generate information important for the immune system. Its structure shows how transport proteins in the membrane, folding enzymes and MHC-I molecules are working together precisely within a highly dynamic complex.

“Our research shows how the MHC-I peptide-loading complex filters out only those fragments of information which are actually needed by the immune system’s effector cells. These findings have solved a decades-old puzzle and allow us now to describe the antigen selection process with greater precision. This knowledge will help to further improve immunotherapies,” concludes Professor Robert Tampé from the Institute of Biochemistry.

Publication: Andreas Blees, Dovilė Janulienė, Tommy Hofmann, Nicole Koller, Carla Schmidt, Simon Trowitzsch, Arne Moeller & Robert Tampé: Structure of the human MHC-I peptide-loading complex, NATURE (Nov 6, 2017, First Release) doi:10.1038/nature24627

A picture can be downloaded from: www.uni-frankfurt.de/69093715

Caption: Structure of the MHC-I peptide-loading complex in the membrane of the endoplasmic reticulum.

Image rights: Arne Möller (Max Planck Institute of Biophysics), Simon Trowitzsch and Robert Tampé (Goethe University Frankfurt)

Further information: Professor Dr. Robert Tampé and Dr. Simon Trowitzsch, Institute of Biochemistry, Faculty of Biochemistry, Chemistry and Pharmacy, Riedberg Campus, Tel.: +49(0)69-798-29475, Tel.: +49(0)69-798-29273, tampe@em.uni-frankfurt.de, Trowitzsch@biochem.uni-frankfurt.de; Dr. Arne Möller, Max Planck Institute of Biophysics, Tel.: +49(0)69-6303-3057, arne.moeller@biophys.mpg.de.

FRANKFURT. A team of Frankfurt-based archaeologists has returned from the Iraqi-Kurdish province of Sulaymaniyah with new findings. The discovery of a loom from the 5^th to 6^th century AD in particular caused a stir.

The group of Near Eastern archaeology undergraduates and doctoral students headed by Prof. Dirk Wicke of the Institute of Archaeology at Goethe University were in Northern Iraq for a total of six weeks. It was the second excavation campaign undertaken by the Frankfurt archaeologist to the approximately three-hectare site of Gird-î Qalrakh on the Shahrizor plain, where ruins from the Sasanian and Neo-Assyrian period had previously been uncovered. The region is still largely unexplored and has only gradually opened up for archaeological research since the fall of Saddam Hussein.

The objective of the excavations on the top and slope sections of the settlement hill, some 26 meters high, was to provide as complete a sequence as possible for the region's ceramic history. Understanding the progression in ceramics has long been a goal of research undertaken on the Shahrizor plain, a border plain of Mesopotamia with links to the ancient cultural regions of both Southern Iraq and Western Iran. These new insights will make it easier to categorise other archaeological finds chronologically. The excavation site is ideal for establishing the progression of ceramics, according to archaeology professor Dirk Wicke: "It is a small site but it features a relatively tall hill in which we have found a complete sequence of ceramic shards. It seems likely that the hill was continuously inhabited from the early 3rd millennium BC through to the Islamic period."

However, the archaeologists had not expected to find a Sasanian loom (ca. 4th-6th century AD), whose burnt remnants, and clay loom weights in particular, were found and documented in-situ. In addition to the charred remains, there were numerous seals, probably from rolls of fabric, which indicate that large-scale textile production took place at the site. From the neo-Assyrian period (ca. 9th-7th century BC), by contrast, a solid, stone-built, terraced wall was discovered, which points to major construction work having taken place at the site. It is possible that the ancient settlement was refortified and continued to be used in the early 1st millennium BC.

Work on the project was initiated by Prof. Wicke in 2015 with support from the local Antiquities Service as well as the Enki e.V. association situated at Goethe University and the Thyssen Foundation. Work is set to continue next year depending on further funding and the political development in the Iraqi-Kurdish region.

Images to download can be found under the following link: http://www.uni-frankfurt.de/68944552

Image captions:

Image 1: Aerial view of the site from the south showing the excavation areas on the summit and south-western slope as well as the small test pit on the south-eastern slope. Photo: Philipp Serba           

Image 2: Neo-Assyrian cylinder seal and imprint on right, height 3.9 cm. It depicts two winged genies on a sacred tree. Photo: Dr. Jutta Eichholz

Image 3: Excavated corner of room with remnants of the loom between the wall (top) and a bench of six mudbricks. The round loom weights made from clay are particularly visible, as are slabs of mud once forming some kind of shelving. Photo: Lanah Haddad

Information: Prof. Dr. Dirk Wicke, Institute of Archaeologicaly, Near Eastern Archaeology, Norbert-Wollheim-Platz 1, 60629 Frankfurt am Main, Germany, Telephone +49 (0)69 798 32317, Secretary's Office +49 (0)69 798 32313

FRANKFURT. The surface of every cell contains receptors that react to external signals similar to a “gate”. In this way, the cells of the innate immune system can differentiate between friend and foe partly through their “toll-like receptors” (TLRs). Two parts of this gate often work together here, as researchers at Goethe University Frankfurt and their British colleagues have now found out with the help of a new super-resolution optical microscopy technique.

When the German Nobel Prize winner Christiane Nüsslein-Volhard discovered receptors in the fruit fly (Drosophila melanogaster) in the 1990s that transduced signals from the cell surface into a cellular response, she was amazed. She nicknamed the receptors “toll” (amazing) and this term has meanwhile become firmly established in scientific literature. Since then, similar receptors (toll-like receptors) have also been discovered in animals and humans. They recognize bacteria, viruses and fungi and thus ensure that our body reacts to infections in a suitable way. By contrast, de-regulated TLRs can lead to chronic inflammatory conditions and cancer.

Experiments conducted so far indicated that TLRs are activated by a chemical signal that causes two proteins to cluster together as dimers. This process, which is known as “dimerization”, appears to play a pivotal role in a cell’s fate: It can decide whether the cell survives, dies or moves within the body. Because dimerization takes place on a molecular scale that cannot be captured using conventional microscopy techniques, researchers have to date been dependent on indirect measuring methods. These were, however, prone to error and yielded diverging results. This has now changed thanks to the new super-resolution optical microscopy technique.

In the forthcoming issue of “Science Signaling”, the working groups led by Professor Mike Heilemann of Goethe University Frankfurt and by Dr. Darius Widera and Dr. Graeme Cottrell of the University of Reading in England describe how they have studied the organization of the TLR4 receptor on the cell surface in molecular resolution. In a first step, they used a super-resolution microscope with a resolution about 100 times better than a standard fluorescence microscope. Since this was still not sufficient to make single receptor molecules in a tiny protein dimer visible, the researchers developed a more sophisticated analysis of the optical signal. In this way they were able to zoom in closer on the super-resolution images and examine under which conditions TLR4 forms a monomer or a dimer. The researchers could also detect which chemical signals from different pathogens modulate the receptors’ patterns.

The researchers hope that their work will lead in future to a better understanding of how TLR dimerization affects the decision between the life or death of a cell. It might also be possible to determine how pharmaceutical ingredients targeted at TLRs influence the behavior of cancer cells. “It is also conceivable that this approach will help us in future to understand better the fundamental biological processes that regulate the immune system in health and disease. At the same time, this microscopy method is also applicable to other membrane proteins and many similar questions,” explains Professor Mike Heilemann from the Institute of Physical and Theoretical Chemistry at Goethe University Frankfurt.

Publication:

Carmen L. Krüger, Marie-Theres Zeuner, Graeme S. Cottrell, Darius Widera, Mike Heilemann: Quantitative single-molecule imaging of TLR4 reveals ligand-specific receptor dimerization, Science Signaling, doi: 10.1126/scisignal.aan1308

A picture can be downloaded under http://www.muk.uni-frankfurt.de/68944753

Caption:

Left: Conventional light microscopy is an useful tool in visualising biological structures and processes. However, its resolution is not sufficient to study events occurring at molecular scale. The image on the left shows the nuclei of brain tumour cells (yellow: nuclei containing DNA) with Toll-like receptors 4 localised at the cell surface (cyan spots).  Although many TLR4 can be clearly seen, the spatial resolution does not allow determination of single receptor units.  Middle: Super-resolution microscopy greatly improves the spatial resolution and allows detection of single TLR4 clusters (cyan) at the surface of the cells. However, even at this superior resolution, it is not possible to distinguish between monomers and dimers of the receptor. Right: Crystal structure of a TLR4 dimer. The novel analysis method developed by the consortium is able to provide information allowing differentiating between receptor monomers and dimers.

Copyright: Widera/Heilemann

Further information: Professor Mike Heilemann, Institute of Physical and Theoretical Chemistry, Faculty of Biochemistry, Chemistry and Pharmacy, Riedberg Campus, Tel.: +49(0)69-798- 29736, Heilemann@chemie.uni-frankfurt.de.

FRANKFURT. The immune system monitors the health status of the cells in our bodies by examining a kind of molecular passport. Sometimes cells present the wrong passport, which can lead to autoimmune diseases, chronic inflammation, or cancer. In the new issue of the journal "Science" (first release), scientists of the Goethe University Frankfurt have now elucidated the mechanism of how the correct molecular passport is selected.

Most cells provide the T cells of the adaptive immune system with information about their condition by presenting selected components of their interior (antigens) on their surface. If these components include fragments of viruses or altered cell components, the affected cell is eliminated by the T cells. The selection of the antigens is crucial in this process. Presenting the wrong antigens leads to either healthy cells being attacked by the immune system - causing autoimmune diseases or chronic inflammation - or to diseased cells not being recognized, allowing cancer cells or virus-infected cells to escape immune surveillance.

Dr. Christoph Thomas and Prof. Robert Tampé from the Institute of Biochemistry at Goethe University have now unraveled on a molecular level how antigens are selected in the cell for presentation on the cell surface. The protein structure they present shows for the first time the kind of quality control antigens undergo to enable a precise and effective immune response.

"Our work solves a 30-year-old problem of cellular immunity, in particular how antigens associated with tumors or pathogens are selected through processes of editing and quality control in order to generate a specific immune response", explains Prof. Robert Tampé the significance of the publication.

Publication:

Christoph Thomas, Robert Tampé: Structure of the TAPBPR–MHC I complex defines the mechanism of peptide loading and editing, Science (Oct 12, 2017, First Release)

An image for download can be found here:

https://www.dropbox.com/s/t4k1u37h01s0p20/TAPBPR_complex_space_filling.png?dl=0

Image captation: Space-filling model of the solved protein complex responsible for antigen selection.