Biology subjects

Ritter, I.

Publications and source records attributed to Ritter, I..

3 recordsLinked to original sources

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↗

bioRxiv2024

Structural plasticity of bacterial ESCRT-III protein PspA in higher-orderassemblies

Eukaryotic members of the endosome sorting complex required for transport III (ESCRT-III) family have been shown to form diverse oligomeric assemblies. The bacterial phage shock protein A (PspA) has recently been identified as a bacterial member of the ESCRT-III superfamily, and monomeric PspA homo-oligomerizes to form large rod-shaped assemblies. As observed for eukaryotic ESCRT-III, PspA forms different tubular assemblies with varying diameters. Using electron cryo-microscopy (cryo-EM), we determined a total of 61 PspA structures and observed in molecular detail how structural plasticity of PspA rods is mediated by conformational changes at three hinge regions in the monomer and by the fixed as well as changing molecular contacts between protomers. Moreover, we reduced and increased the structural plasticity of PspA rods by removing the loop connecting helices 3/4 and the addition of nucleotides, respectively. Based on our analysis of PspA-mediated membrane remodeling, we suggest that the observed mode of structural plasticity is a prerequisite for the biological function of ESCRT-III superfamily members. SummaryA series of cryo-EM structures of PspA rods with induced diameter modulations reveals the molecular basis of structural plasticity.

biophysics↗