Dynamics of the ESCRT machinery during MVB biogenesis

The selective degradation of cellular components is essential for the survival and the growth of all eukaryotic cells. The degradation of membrane proteins, such as growth factor receptors, requires a molecular machinery, the so-called endosomal sorting complexes required for transport (ESCRT). This machinery identifies membrane proteins that are destined for degradation and sends them along a sophisticated transport pathway into lysosomes, where they are destroyed upon arrival. To do so the ESCRT machinery generates unusual transport vesicles, named multivesicular bodies (MVB). During the production process for these MVBs, the ESCRT machinery executes a topologically unique membrane remodeling reaction that bends membrane away from the cytoplasm. Similar membrane remodeling reactions are required in different biological processes including budding of HIV and during cell division. Just how the ESCRT machinery molds membranes remains a major mystery in biology that we plan to address with this project. Addressing these questions will require a combination of state-of-the- art genetics, imaging and biochemical approaches. By connecting quantitative, dynamic and mechanistic data with membrane shape information we will gain systems level understanding of the ESCRT pathway leading to membrane remodeling. Hence our results may provide unifying principles of ESCRT mediated membrane remodeling.

The selective degradation of cellular components is essential for the survival and the growth of all eukaryotic cells. The degradation of membrane proteins, such as growth factor receptors, requires a molecular machinery, the so-called 'endosomal sorting complexes required for transport' (ESCRT). This machinery identifies membrane proteins that are destined for degradation and sends them along a sophisticated transport pathway into lysosomes, where they are destroyed upon arrival. To do so the ESCRT machinery generates unusual transport vesicles, named multivesicular bodies (MVB). During the 'production process' for these MVBs, the ESCRT machinery executes a topologically unique membrane remodeling reaction that bends membrane away from the cytoplasm. Similar membrane remodeling reactions are required in different biological processes including budding of HIV and during cell division. Just how the ESCRT machinery molds membranes remains a major mystery in biology that we had proposed to address with this project. Towards this goal we have used a combination of state-of-the-art genetics, imaging and biochemical approaches. By connecting quantitative, dynamic and mechanistic data with membrane shape information we have gained a detailed understanding of the ESCRT pathway leading to membrane remodeling. Our research project revealed that ESCRT-III and Vps4 form dynamic assemblies on membranes. In these dynamic ESCRT-III/Vps4 assemblies, the ATPase activity of Vps4 hexamers is required to drive membrane invagination towards the point of scission, most likely through mechanochemical coupling to the ESCRT-III polymers and force generation. Hence our results provide unifying principles of ESCRT mediated membrane remodeling.