News
X-mas party 2012
You will find some impressions of the Christmas celebration 2013 here...X-mas 2012
Reinhart Koselleck Project for p63 research: 1 million EUR funding
FRANKFURT, January 12th 2012: For the research on oocyte quality control Prof. Dötsch receives 1 Mio Euro funding from the DFG. The basis for granting this high risk project are the recently published results of his group (see below, Deutsch, G. et al., Cell 144(4) 566-567 (2011)
X-mas party 2011
You will find photos of the Christmas celebration on December 15th here...X-mas 2011
Ernst-Award for Robert Hänsel
FRANKFURT, August 21.-25. 2011: Nobel laureate Richard Ernst visited the EUROMAR 2011 held in Frankfurt, the annual conference for magnetic resonance spectroscopy. He handed over himself the “Ernst-Award” to young scientists for their contribution in reputable scientific journals. Robert Hänsel (Dötsch group) and Ivan Krstic (Prisner group) were awarded for establishing an EPR method to measure global structural changes of spin labeled nucleic acids directly in living cells Angew Chem Int Ed Engl. 50(22):5070–507 (2011), thus complementing a more recently published in-cell NMR method to characterize nucleic acid structure under cellular conditions J. Am. Chem. Soc. 131, 15761-15768 (2009).
Volker Dötsch became new member of EMBO
FRANKFURT, October 20th 2011: Prof. Dr. Volker Dötsch is one of the 46 outstanding life scientists elected to EMBO membership this year. Currently, 1400 leading scientist in the field of molecular life sciences are members of the European Molecular Biology Organization. You will find a complete list of the new members using this link
A chaperone system guids tail-anchored membrane proteins to their destined membrane - Molecular mechanism resolved
New publication in Science: Stefer, S. et al., Science, 333: 758-62
FRANKFURT. A newly synthesized protein is as fragile as a newborn baby. It could never fold into its correct three dimensional structure if it would not be protected by chaperones within the densely populated cytosol. In case of membrane proteins chaperones do not only prevent their aggregation, but also escort them to their destination and aid in membrane insertion. The underlying molecular mechanism of how a certain family of membrane proteins is targeted and inserted into membranes has now been resolved by an international research team with participation of the Goethe University Frankfurt. These proteins are anchored within the membrane via a single helix and thus are called “tail-anchored” (TA) proteins. The key for proper protein sorting are signal sequences which are decoded by chaperones. As soon as they - together with their “foster child” - arrive at their destination the interaction with a specific receptor within the target membrane initiates membrane insertion. Protein components responsible for the insertion of TA proteins have recently been identified. The molecular mechanisms of how these sorting systems work, however, were not known so far. In this interdisciplinary study, that will be released in the current “online” issue of “Science”, the re-search groups of Prof.Volker Dötsch (Goethe University Frankfurt), Prof. Irmgard Sinning (Heidelberg University Biochemistry Center) and Prof. Vlad Denic (Harvard University (USA)) were able to solve the question by a combination of diverse methods such as X-Ray Crystallography and NMR-Spectroscopy as well as biochemical and cell-biological approaches. In detailed biophysical studies Volker Dötsch´s research group showed that the central chaperon of the responsible protein complex, called Get3, regulates both binding to TA proteins within the cytosol and their release at the membrane. The two receptor proteins Get1 and Get2 aid in TA protein insertion. They use overlapping interfaces for the interaction with the Get3 ATPase. On the basis of different crystal structures the researchers suggest a model for the mechanism of how TA proteins are inserted into the membrane. Upon interaction with its membrane receptor the Get3 dimer gradually opens up to allow for the controlled TA protein insertion. “Those results are particularly important because they enabled us to establish the first model of the receptor-assisted membrane insertion of TA proteins that will now be the basis for further studies” comments Dötsch.
Crystal structure of the Get3/Get1 complex solved in this study. The two Get3 monomers that form the functional dimer are shown in green and in blue. Each monomer binds one Get1 molecule, colored in red and orange. Get1 binds into the cleft between the Get3 monomers and initiates a conformational change that leads to a more open structure. This opening is a prerequisite for TA protein release from Get3 and subsequent insertion into the membrane.
Information:
Prof. Dr. Volker Dötsch
Institute of Biophysical Chemistry
Campus Riedberg
Tel: +49 69 798-29631
vdoetsch@em.uni-frankfurt.de
Lab Trip 2011 - Canoeing
You will find pictures of our recent excursion on the Lahn using the following link: Canoeing Lahn 2011
Female quality control in oocytes
Inactive dimers – active tetramers: the importance of the p53 protein family for the development and health of human beings
Deutsch, G. et al., Cell 144(4) 566-567 (2011)
Chemotherapeutic agents, used in cancer treatment, destroy not only cancer cells but also healthy cells, thus affecting germ cells as well. Consequently, after surviving cancer many female patients are confronted with the diagnosis: infertility. For a long time a relationship between infertility and chemotherapeutic agents has been assumed, but until now, the exact mechanism was not known. Scientists from the research group of Prof. Volker Dötsch (Institute of Biophysical Chemistry, Goethe University Frankfurt) in cooperation with international partners have now started to unveil the mechanism of cancer treatment related infertility. Their results are published in the internationally renowned journal Cell. Mainly women suffer from infertility because the quality control in the oocytes is different from male germ cells. Male germ cells are produced throughout the whole life span but the number of female germ cells is restricted and already fixed before birth. If the oocytes are damaged during cancer treatment, they are destroyed by the female quality control mechanism. Essential for this process is the protein p63 which shows striking similarity to another important protein of the same family: p53. p53 is also named “guardian of the genome” because of its regulatory function in cell division and cell death of damaged cells and, therefore, plays a key role in the suppression of genetic anomalies which could lead to cancer. In more than half of all human tumors p53 is altered and no longer functional. For a long time the exact regulation of p53 and p63 and the similarities and differences between these two proteins have been the object of many international research projects. In the currently accepted model the concentration of p53 in healthy cells is relatively low. If genetic anomalies occur in a cell which could cause the transition to a cancer cell, the concentration of p53 increases and four p53 proteins form a tetramer. In this tetrameric state the tumor suppressor is active and initiates either repair of the damaged DNA or programmed cell death. Surprisingly, despite the fact that p53 and p63 show high similarity, the mechanism by which the activity of p63 is controlled in oocytes seemed to be different.
The research group of Prof. Volker Dötsch could show now that the two mechanisms that regulate the activity of p53 and of p63 are closely related, but distinct. The level of p63 in normal oocytes is high and the protein is kept in a closed dimeric and inactive state. If DNA double-strand breaks occur, for example caused by radioactive radiation, p63 becomes phosphorylated. As a result of this phosphorylation, the structure of the p63 dimer changes to an open state allowing the attachment of a second phosphorylated dimer. The resulting active p63 tetramer is similar to the active p53 tetramer and leads to the death of the damaged oocyte. Many of the chemotherapeutic agents cause DNA double-strand breaks which activate p63, finally leading to the cell death of the oocytes. The related proteins of model organisms such as Caenorhabditis elegans (nematode) are also investigated by the Dötsch group. Because of the short life span of this worm its p63 related protein does not act as a tumor suppressor but controls the genetic stability of the germ cells. The quality control of germ cells, thus, seems to be the original function of the p53 protein family and leads to the conclusion that p63 is the ancestor of the entire p53 family. Interestingly, p63 shows an additional function: it is essential for the maintenance of stem cells in epithelial layers like skin. Because of the close similarity of stem and germ cells, this second function shows the evolutionary process of the p53 protein family from p63-like proteins, that in simple organisms are responsible for the genetic stability of germ cells, via controlling the maintenance of stem cells in organisms with renewal tissues, finally to p53-like tumor repressors in somatic cells. This demonstrates the outstanding importance of the p53 protein family for the development and health of human beings.
For more information:
Prof. Dr. Volker Dötsch, Institute for Biophysical Chemistry, Max-von-Laue-Str. 9, 60438 Frankfurt am Main
phone: +49 69 798 29631, email: vdoetsch(at)em.uni-frankfurt.de
Presenilin and the development of Alzheimer
Researchers at the Goethe University in Frankfurt have solved the structure of C-terminal domain of presenilin: Sobhanifar S. et al., PNAS USA 107, 9644–9649 (2010)
The increase in life expectancy in the industrialized states has resulted in an increase in the number of patients suffering from dementia. 60% of these dementia are due to Alzheimer’s disease which is caused by the death of certain neurons in the brain. Characteristic for Alzheimer’s disease is deposition of plaques consisting of amyloid beta peptide. According to the current model it is not these plaques but rather oligomeric and soluble precursors that are responsible for neuronal death. If the formation of the beta amyloid protein could be suppressed, the production of these oligomers would be suppressed as well. Central to the process of amyloid beta peptide formation is the enzymatic activity of presenilin. So far the structure of this protease was not available. As typical for membrane proteins characterization of its structure met great difficulties with the well established classical methods of x-ray crystallography or NMR spectroscopy. A research team headed by Volker Dötsch was now successful in determining the structure of the C-terminal domain of presenilin, as they report in the „Proceedings of the National Academy of Sciences“. The topology of this C-terminal domain that harbors one of the two catalytic aspartate residues was so far highly controversial and predictions were based on computational modeling and indirect biochemical experiments. To investigate the structure of the C-terminal domain the research group of Volker Dötsch used a method that has been developed at the Institute of Biophysical Chemistry for several years. The group of Frank Bernhard had shown that membrane proteins can be obtained in the large amounts required for detailed structural studies by isolating the protein synthesis machinery from E. coli and reconstituting protein synthesis in vitro in a test tube. This method of protein production enabled the development of novel NMR techniques that made the investigation of membrane proteins in isolated micelles possible.
The structure of the C-terminal domain now solved is the first high resolution structure of any of the components of the γ-secretase, the multi-component membrane protein complex that is responsible for producing the amyloid beta peptide by proteolytically cutting the amyloid beta precursor protein and of which presenilin is the most important component. The structure shows that the C-terminal domain consists of three helical regions that traverse the membrane. Of these, however, only one is a typical transmembrane helix – a fact that explains the difficulty in predicting the topology of this domain by pure computational approaches. The catalytic aspartate is located at the N-terminus of one of the helices which, however, is too short to fully traverse the membrane, thus placing the catalytic residue in the middle of the membrane. However, by additional experiments the research group of Volker Dötsch could show that the aspartate is surrounded by a hydrophilic environment. This finding is consistent with the results from single particle cryo-electron microscopy of the entire γ-secretase complex which has shown that in the center of this enzyme complex a large water filled cavity exists in which proteolysis is believed to take place (Lazarov et al., PNAS 2006; Osenkowski et al., JMB 2009). The final transmembrane helix of the C-terminal domain shows a highly kinked and unusual structure due to the presence of a proline in the middle of the helical region. This unusual helical structure has been implicated in being involved in substrate binding and a very similar structural element has been identified in the structure of the rhomboid protease, a bacterial membrane bound enzyme. In addition to these three membrane embedded helical regions the structure revealed the presence of another helix in a long so far believed to be completely unstructured loop that lies at the interface between the cytoplasm and the membrane. Interestingly, several mutations implicated in early onset familial Alzheimer disease are located in this newly discovered helix.
