Biology subjects

Kutzner, M.

Publications and source records attributed to Kutzner, M..

3 recordsLinked to original sources

bioRxiv2025

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

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.

biochemistry↗

bioRxiv2025

The bacterial ESCRT-III PspA rods thin lipid tubules and and increase membrane curvature through helix α0 interactions

The phage shock protein A (PspA), a bacterial member of the ESCRT-III superfamily, forms rod-shaped helical assemblies that internalize membrane tubules. The N-terminal helix 0 of PspA (and other ESCRT-III members) has been suggested to act as a membrane anchor, the detailed mechanism, however, of how it binds to membranes and eventually triggers membrane fusion and/or fission events remains unclear. By solving a total of 15 cryo-electron microscopy (cryo-EM) structures of PspA and a truncation lacking the N-terminal helix 0 in the presence of EPL membranes, we show in molecular detail how PspA interacts with and remodels membranes: binding of the N-terminal helix 0 in the outer tubular membrane leaflet induces membrane curvature, supporting membrane tubulation by PspA. Detailed molecular dynamics simulations and free energy computations of interactions between the helix 0 and negatively charged membranes suggest a compensating mechanism between helix/membrane interactions and the energy contributions required for membrane bending. The energetic considerations are in line with the membrane structures observed in the cryo-EM images of tubulated membrane vesicles, fragmented vesicles inside tapered PspA rods, and shedded vesicles emerging at the thinner PspA rod ends. Our results provide insights into the molecular determinants and a potential mechanism of vesicular membrane remodeling mediated by a member of the ESCRT-III superfamily. SummaryThe rods of bacterial ESCRT-III protein PspA internalize and thin membrane tubules by overcoming the required bending energy through progressive membrane binding of the N-terminal helix in the PspA assembly.

biophysics↗

bioRxiv2024

Structural basis for Vipp1 membrane binding: From loose coats and carpetsto ring and rod assemblies

Vipp1 (also known as IM30) is essential in most oxygenic photoautotrophic organisms. It is involved in membrane remodeling and fusion and is critical for thylakoid membrane biogenesis and maintenance. Vipp1 has recently been identified as a member of the ESCRT-III superfamily of membrane remodeling proteins, albeit it still is elusive how Vipp1 interacts with and finally remodels membranes. Here we present a series of cryo-EM structures of cyanobacterial Vipp1 interacting with bacterial membranes: first, we solved seven structures between 5 and 7 [A] resolution of three unique helical and four types of stacked-ring assemblies engulfing membranes, and, second, using sub-tomogram averaging, we determined three [~]20 [A] resolution structures compatible with previously observed carpet structures at three different membrane curvatures. By analyzing ten additional unique structures of N-terminally truncated Vipp1, we could show that helix 0 is essential for membrane tubulation and forms the membrane anchoring domain of Vipp1. Using a conformation-restrained Vipp1 mutant, we were able to reduce the structural plasticity of Vipp1 assemblies in the presence of lipids and determined two structures of Vipp1 at 3.0 [A] resolution, resolving the molecular details of membrane anchoring and intersubunit contacts of helix 0. Our data reveal the molecular details of how Vipp1 interacts with membranes, showing membrane curvature-dependent structural transitions from carpets to rings and rods, some of which are capable of inducing and/or stabilizing high local membrane curvature triggering membrane fusion. SummaryBacterial ESCRT-III family member Vipp1 forms membrane-bound coats, carpets, ring complexes, stacked-ring assemblies and helical tubes capable of internalizing lipids and inducing high membrane curvature.

biophysics↗