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BioSoft Colloquium:

Cryo-EM reveals structures of ESCRT-III membrane remodeling proteins in eukarya and bacteria

Carsten Sachse

Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons
Forschungszentrum Jülich


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17 Jun 2021 11:00
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Abstract:

Theoretical Physics Copyright: Carsten Sachse, ER-C

ESCRT-III proteins are known to mediate a range of eukaryotic membrane remodeling activities such as multivesicular body biogenesis, cytokinesis and viral release. Critical to these processes is the assembly of ESCRT-III subunits into polymeric structures. The exact atomic-level details of how ESCRT-III monomers come together and facilitate membrane remodeling remain to be established.

Recently, we determined the cryo-EM structure of a helical assembly of S. cerevisiae Vps24 at 3.2 Å resolution and found that Vps24 adopts an elongated open conformation. Vps24 forms a domain-swapped dimer extended into protofilaments that associate into a double stranded apolar filament. The filamentous Vps24 homopolymer assembly structure and interaction studies reveal how Vps24 could introduce unique geometric properties to mixed type ESCRT-III heteropolymers and contribute to the process of membrane scission events.

More recently, we determined the 3.6 Å resolution cryo-EM structure of bacterial PspA assembled in helical rods. PspA, the main effector of the phage shock protein (Psp) response, preserves the integrity and functions of the bacterial inner membrane. Unexpectedly, the structure reveals that PspA adopts a canonical ESCRT-III fold in an extended open conformation so far unknown in bacteria. PspA rods are capable of enclosing lipids and generate positive membrane curvature.

Using cryo-EM we visualized how PspA remodels membrane vesicles into μm-sized structures and how it mediates the formation of internalized vesicular structures. Hot spots of these activities are zones derived from PspA assemblies, serving as lipid transfer platforms and linking previously separated lipid structures. These membrane fusion and fission activities are in line with the described functional properties of bacterial PspA/IM30/LiaH proteins. Our structural and functional analyses reveal that bacterial PspA belongs to the evolutionary ancestry of ESCRT-III proteins involved in membrane remodeling.

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