Research group for Biochemistry of signal dynamics,
MPI for Multidisciplinary Sciences, Göttingen, Germany
Building a survival machinery in time: how HORMA domains regulate human autophagy initiation
Autophagy quickly forms cup-shaped structures known as 'autophagosomes' for degradation/recycling of different cell componentsto ensure cell survival under stress. How the autophagy initiation machinery is rapidly assembled at the ER remains unknown. Therefore, we biochemically reconstituted the initiation complexes and proposed the complex composed of ATG13-ATG101 and the lipid scramblase ATG9 ('core complex') to be the rate-limiting step
in autophagy initiation. The dimerization of ATG101 and ATG13 accelerates the interaction with ATG9 and ATG13 can alter its tertiary structure reversibly. This alteration not only
controls the dimerization but also affects the HORMA domain proteins interaction spectrum. Furthermore, we discovered that ATG13-ATG101-ATG9 connects various initiation subcomplexes that together form a 'super-complex', lending support to the idea that the ATG13-ATG101-ATG9 formation is the kinetic bottleneck controlling the initiation machinery assembly at the ER contact site, critical for autophagosome biogenesis. These findings anticipate quantitative analysis to explain how the autophagy initiation complex promotes autophagosome initiation in space and time.
"I joined the MPI of Göttingen as a PhD candidate in 2017, just after receiving a Master’s Degree in “Molecular, cellular, and biomedical Sciences” from the University of Rome TorVergata. During my Master’s, for two years, I worked in the Institute in Rome founded by the Nobel Prize winner Rita Levi Montalcini in Dr. Puri’s lab. These years my interest was focused on ALS, muscular atrophy, and autophagy from the cell biology point of view and culminated with a publication. What drove me toward biochemistry was my need to see these processes at a more detailed level. I joined Alex Faesen’s Lab as his first Ph.D. student to study autophagy initiation while investigating the unknown role of two HORMA domain proteins, ATG13 and ATG101. In March 2022 I received a Ph.D. degree from the University of Göttingen with the work I am going to present at the Horizon Conference."
Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.
Reconstituting mouse embryogenesis ex utero
In mammals, all the main organs appear soon after the embryo implants into the uterus, and proper embryonic development is dependent on its interaction with the maternal tissues. Yet, the small size and intrauterine confinement of the embryos has limited the study of post-implantation embryogenesis. We devised highly efficient platforms for continuous ex utero culture of early post-implantation mouse embryos, which enable proper development of embryos between pre-gastrulation (day E5.5) until the hindlimb formation stage (day E11). Further, we developed an extended culture platform for growing embryos ex utero from the totipotent zygote through implantation, gastrulation and organogenesis. These culture systems allow the introduction of a variety of embryonic perturbations, which can be followed ex utero in living mouse embryos. Finally, by combining the ex utero culture platform with stem cell-embryo models, we successfully established stem cell-synthetic embryos that capture full gastrulation and early organogenesis, assembled solely from naïve pluripotent stem cells. These results provide a proof-of-concept for the ability to capture mammalian development from fertilization to organogenesis in an ex utero environment, and underscore the self-organizing ability of the embryo.
Alejandro Aguilera Castrejon, born in Mexico, obtained a B.Sc. in biology (2015) at the National Autonomous University of Mexico, performing his thesis research at the Institute for
Cellular Physiology by working on direct reprogramming of bone marrow mesenchymal stem cells into neurons. In 2016, he moved to Israel for his M.Sc and PhD. degrees in Life Sciences at the Weizmann Institute of Science, under the supervision of Prof. Jacob Hanna. Since then, Alejandro has been focusing on devising platforms for growth of mammalian embryos outside the uterus, harnessing these new platforms for studying the mechanisms regulating early
Department of Molecular Biology, Max Planck Institute for multidisciplinary sciences
Mechanism of molnupiravir-induced SARS-CoV-2 mutagenesis
Molnupiravir is an orally available antiviral drug candidate currently in phase III/ IV trials for the treatment of patients with COVID-19. Molnupiravir increases the frequency of viral RNA mutations and impairs SARS-CoV-2 replication in animal models and in humans. We establish the molecular mechanisms underlying molnupiravir-induced RNA mutagenesis by the viral RNA-dependent RNA polymerase (RdRp). Biochemical assays show that the RdRp uses the active form of molnupiravir, β-D-N4-hydroxycytidine (NHC) triphosphate, as a substrate instead of cytidine triphosphate or uridine triphosphate. When the RdRp uses the resulting RNA as a template, NHC directs incorporation of either G or A, leading to mutated RNA products. Structural analysis of RdRp–RNA complexes that contain mutagenesis products shows that NHC can form stable base pairs with either G or A in the RdRp active center, explaining how the polymerase escapes proofreading and synthesizes mutated RNA. This two-step mutagenesis mechanism probably applies to various viral polymerases and can explain the broad-spectrum antiviral activity of molnupiravir.
Florian Kabinger is a second-year PhD student at the Max Planck Institute for multidisciplinary sciences in the group of Prof. Patrick Cramer. He was awarded with the Boehringer Ingelheim Fonds PhD Fellowship in order to study the molecular basis of viral RNA replication. To dissect the molecular machinery involved in this complex process he utilizes single particle cryo-EM and biochemical assays. In his latest research, he applied these state-of-the-art methods to investigate the mode of action of the drug candidate Molnupiravir. Florian Kabinger did his Bachelor´s program and Master´s program at the University for applied life sciences Vienna. During that period he also conducted research projects at the University of Stockholm (Sweden) and Massachusetts Institute of Technology (USA). Experiencing the power of structural biology paired with drug development inspired his current research.