Membrane binding of a cyanobacterial ESCRT-III protein crucially involves the helix α1-3 hairpin conserved in all superfamily members

Schlösser, L.; Kutzner, M.; Hellmann, N.; Kiesewetter, D.; Bieber, J.; Quarta, N.; Ge, X.; Goetze, T.; Junglas, B.; Matsumura, F.; Bonn, M.; Gräter, F.; Sachse, C.; Liu, L.-N.; Schmidt, C.; Aponte-Santamaria, C.; Schneider, D.

doi:10.1101/2025.09.05.674404

bioRxiv · 10.1101/2025.09.05.674404

Membrane binding of a cyanobacterial ESCRT-III protein crucially involves the helix α1-3 hairpin conserved in all superfamily members

Schlösser, L.·Kutzner, M.·Hellmann, N.·Kiesewetter, D.·Bieber, J.·Quarta, N.·Ge, X.·Goetze, T.·Junglas, B.·Matsumura, F.·Bonn, M.·Gräter, F.·Sachse, C.·Liu, L.-N.·Schmidt, C.·Aponte-Santamaria, C.·Schneider, D.

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Abstract

IM30, the inner membrane-associated protein of 30 kDa (also known as Vipp1) is essential for thylakoid membrane biogenesis and/or maintenance in chloroplasts and cyanobacteria. IM30 and its bacterial homolog PspA belong to the ESCRT-III superfamily, proteins previously thought to be restricted to eukaryotes and archaea. Despite low sequence similarity, IM30 shares key structural and functional features with eukaryotic ESCRT-IIIs, including a conserved 1-2 helical hairpin core and the ability to form oligomeric barrel- or rod assemblies that mediate membrane remodeling. Using IM30 variants, we now show that initial membrane recruitment of IM30 is driven by electrostatic interactions between the positively charged 1-3 helical hairpin and negatively charged lipid surfaces, paralleling the role of charged helical regions in some eukaryotic ESCRT-IIIs. This likely initiates lateral assembly of IM30 into higher-order barrel or rod structures on the membrane. Once assembled, 0 helices within these oligomers engage and stabilize internalized membrane tubules, mirroring membrane interaction strategies of eukaryotic ESCRT-IIIs, which use both N-terminal sequences and charged residues on 1/2. Thus, our findings demonstrate a conserved membrane binding and remodeling mechanism across the ESCRT-III superfamily, underscoring an evolutionary link in membrane dynamics between pro- and eukaryotes. SignificanceIM30, a membrane-associated protein found in cyanobacteria and chloroplasts, along with its bacterial homolog PspA, belongs to the ESCRT-III superfamily. Despite low sequence conservation, these proteins share structural and functional features with eukaryotic ESCRT-III proteins. We show that IM30 binds membranes via a conserved structural motif, followed by lateral assembly into higher-order complexes. This supports a mechanism of membrane remodeling that is conserved in prokaryotic and eukaryotic members of the ESCRT-III superfamily.

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Schlösser, L., Kutzner, M., Hellmann, N., Kiesewetter, D., Bieber, J., Quarta, N., Ge, X., Goetze, T., Junglas, B., Matsumura, F., Bonn, M., Gräter, F., Sachse, C., Liu, L.-N., Schmidt, C., Aponte-Santamaria, C., Schneider, D.. 2025-09-05. Membrane binding of a cyanobacterial ESCRT-III protein crucially involves the helix α1-3 hairpin conserved in all superfamily members. https://doi.org/10.1101/2025.09.05.674404

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