Cells and their internal compartments are surrounded by lipid membranes that need to be remodelled (reshaped, cut, fused) in order to maintain cellular integrity and homeostasis. One of the machineries mediating membrane-remodelling are the Endosomal Protein Complexes Required for Transport (ESCRT)-III. In the lab, we investigate the molecular mechanism of the ESCRT-III machinery in order to understand how it cuts and deforms lipid membranes.
Structure of ESCRT-III assemblies
Membrane-bound ESCRT-III proteins (hetero)polymerise into filaments. Depending on the ESCRT-III subunit composition and/or stoichiometry, the respective filaments display different organisations. We want to solve the structures of membrane-bound ESCRT-III polymers to understand how they control membranes’ shape and orientation. Comparing ESCRT-III polymers on intact membranes with those on detergent-stabilised membranes will give important mechanical insight. To this end, we use cryogenic electron microscopy (cryo-EM) and tomography (cryo-ET).
Dynamic changes within ESCRT-III assemblies
During membrane remodelling, different ESCRT-III subunits are recruited to the membrane and polymerise into filamentous (hetero-)polymers. The ESCRT-III subunits incorporated and/or their respective ratio within the filament change during the remodelling event, under the influence of the AAA ATPase Vps4. This results in different polymer organisations that translate into membrane shape or topology changes. We want to learn how subunits reorganise within a polymer to allow for the structural changes within the filament.
Role of lipids in membrane remodelling
Membranes are the target of the ESCRT-III machinery, but they also play a major role in the machinery’s efficiency. We study how the lipid composition of membranes affects the activity of the ESCRT-III and how it can facilitate membrane deformation and fission. In vitro reconstitutions on artificial membranes allow us to study directly the effect of individual lipids, lipid phases and their respective biophysical features in detail.
Pfitzner A-K, Mercier V, Jiang X, Moser von Filseck J
, Baum B, Šarić A and Roux A “An ESCRT-III Polymerization Sequence Drives Membrane Deformation and Fission” Cell 182, 1-16 (2020). https://doi.org/10.1016/j.cell.2020.07.021
Moser von Filseck J
, Barberi L, Talledge N, Johnson I, Frost A, Lenz M and Roux A “Anisotropic ESCRT-III architecture governs helical membrane tube formation” Nat Commun 11, 1516 (2020). https://doi.org/10.1038/s41467-020-15327-4
Mierzwa BE, Chiaruttini N, Redondo-Morata L, Moser von Filseck J
, König J, Larios J, Poser I, Müller-Reichert T, Scheuring S, Roux A and Gerlich DW “Dynamic subunit turnover in ESCRT-III assemblies is regulated by Vps4 to mediate membrane remodeling during cytokinesis” Nat Cell Biol 19, 787-798 (2017). https://doi.org/10.1038/ncb3559