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Tension of ENDOmembranes maintained by TORC1

Periodic Reporting for period 3 - TENDO (Tension of ENDOmembranes maintained by TORC1)

Reporting period: 2022-05-01 to 2023-10-31

TENDO studies the structure, function and regulation of the two Target Of Rapamycin Complexes, TORC1 and TORC2. These complexes are broadly conserved across eukaryote species and serve fundamental roles in cell and organism homeostasis.
TORC1 and TORC2 have protein kinase activity and thus function in signal transduction pathways that help cells maintain their size: TORC1 regulates cell volume while TORC2 appears to regulate cell surface area. Dysregulation of these particular signaling cascades is associated with diseases such as metabolic disorder, cancer and even aging itself. Ultimately, with a better, ideally molecular or event atomic, understanding of TOR signaling we hope to be able to understand and thus therapeutically manipulate these pathways for therapeutic gain.
The lab has recently made three major breakthroughs in this field. These were based in the model eukaryote S. cerevisiae (bakers' yeast). The first is that TORC1 is regulated via reversible polymerization into a giant helix. In this helical form, the active site of the enzyme is physically occluded and signaling is thus blocked. The second is that TORC2 is regulated by changes in the tension of the plasma membrane. The third is that membrane tension can be altered using small molecules. In TENDO we wish to determine i) if TORC2, like TORC1 is regulated via reversible polymerization; ii) if TORC1 is regulated downstream of biophysical changes in intracellular membranes; and iii) if we can drug membranes as a means to affect TOR signaling.
This work period was far from optimal given the sanitary conditions in Geneva (as elsewhere). Nevertheless, we were able to make some exciting progress regarding the high resolution structures of TORC1 and TORC2 in varying conformations. We have also discovered that membrane tension can indeed be "drugged" in higher eukaryote cells with consequences on mammalian TORC2 signaling output. Lastly, we have exciting, preliminary structures for other elements in the TOR signaling network. Notably, our structural biology projects are set to move much faster as we will have access to state-of-the-art electron cryomicroscopes as of the first quarter 2021. These results are not yet finalized but we hope to start publishing them in 2021.
We are well on track to determine novel TORC1 and TORC2 structures that explain their regulation in vivo. Structure-based hypotheses will be challenged in yeast cells as well as in mammalian systems. Ideally, through a new collaboration we will be able to extent these results with in situ cryoEM (cryoET) to visualize for the first time how the TOR Complexes interact with membranes and the consequence these interactions have on kinase activity. We are already now able to recapitulate in vitro the effects of membranes on TORC kinase activity.
We are keen to get feedback from colleagues in the field regarding our hypothesis that membranes can be bona fide drug targets. With this realization, drug target space becomes drastically increased (presently the vast majority of clinically used drugs target proteins). This change in drug-discovery mindset could have important implications and lead to completely novel approaches to treat disease.
Localization of TORC2 in stationary phase yeast cells