Search results for "Lipid bilayer fusion"

2019

The inner membrane-associated protein of 30 kDa (IM30, also known as Vipp1) is required for thylakoid membrane biogenesis and maintenance in cyanobacteria and chloroplasts. The protein forms large rings of ∼2 MDa and triggers membrane fusion in presence of Mg2+. Based on the here presented observations, IM30 rings are built from dimers of dimers, and formation of these tetrameric building blocks is driven by interactions of the central coiled-coil, formed by helices 2 and 3, and stabilized via additional interactions mainly involving helix 1. Furthermore, helix 1 as well as C-terminal regions of IM30 together negatively regulate ring-ring contacts. We propose that IM30 rings represent the i…

Functional Implications of Multiple IM30 Oligomeric States

2019

The inner membrane-associated protein of 30 kDa (IM30), also known as the vesicle-inducing protein in plastids 1 (Vipp1), is essential for photo-autotrophic growth of cyanobacteria, algae and higher plants. While its exact function still remains largely elusive, it is commonly accepted that IM30 is crucially involved in thylakoid membrane biogenesis, stabilization and/or maintenance. A characteristic feature of IM30 is its intrinsic propensity to form large homo-oligomeric protein complexes. 15 years ago, it has been reported that these supercomplexes have a ring-shaped structure. However, the in vivo significance of these ring structures is not finally resolved yet and the formation of mor…

The IM30/Vipp1 C-terminus associates with the lipid bilayer and modulates membrane fusion.

2017

IM30/Vipp1 proteins are crucial for thylakoid membrane biogenesis in chloroplasts and cyanobacteria. A characteristic C-terminal extension distinguishes these proteins from the homologous bacterial PspA proteins, and this extension has been discussed to be key for the IM30/Vipp1 activity. Here we report that the extension of the Synechocystis IM30 protein is indispensable, and argue that both, the N-terminal PspA-domain as well as the C-terminal extension are needed in order for the IM30 protein to conduct its in vivo function. In vitro, we show that the PspA-domain of IM30 is vital for stability/folding and oligomer formation of IM30 as well as for IM30-triggered membrane fusion. In contra…

Specific interaction of IM30/Vipp1 with cyanobacterial and chloroplast membranes results in membrane remodeling and eventually in membrane fusion.

2016

The photosynthetic light reaction takes place within the thylakoid membrane system in cyanobacteria and chloroplasts. Besides its global importance, the biogenesis, maintenance and dynamics of this membrane system are still a mystery. In the last two decades, strong evidence supported the idea that these processes involve IM30, the inner membrane-associated protein of 30kDa, a protein also known as the vesicle-inducing protein in plastids 1 (Vipp1). Even though we just only begin to understand the precise physiological function of this protein, it is clear that interaction of IM30 with membranes is crucial for biogenesis of thylakoid membranes. Here we summarize and discuss forces guiding I…

Proton Leakage Is Sensed by IM30 and Activates IM30-Triggered Membrane Fusion

2020

The inner membrane-associated protein of 30 kDa (IM30) is crucial for the development and maintenance of the thylakoid membrane system in chloroplasts and cyanobacteria. While its exact physiological function still is under debate, it has recently been suggested that IM30 has (at least) a dual function, and the protein is involved in stabilization of the thylakoid membrane as well as in Mg2+-dependent membrane fusion. IM30 binds to negatively charged membrane lipids, preferentially at stressed membrane regions where protons potentially leak out from the thylakoid lumen into the chloroplast stroma or the cyanobacterial cytoplasm, respectively. Here we show in vitro that IM30 membrane binding…

Mg2+ binding triggers rearrangement of the IM30 ring structure, resulting in augmented exposure of hydrophobic surfaces competent for membrane binding

2018

The "inner membrane-associated protein of 30 kDa" (IM30), also known as "vesicle-inducing protein in plastids 1" (Vipp1), is found in the majority of photosynthetic organisms that use oxygen as an energy source, and its occurrence appears to be coupled to the existence of thylakoid membranes in cyanobacteria and chloroplasts. IM30 is most likely involved in thylakoid membrane biogenesis and/or maintenance, and has recently been shown to function as a membrane fusion protein in presence of Mg2+ However, the precise role of Mg2+ in this process and its impact on the structure and function of IM30 remains unknown. Here, we show that Mg2+ binds directly to IM30 with a binding affinity of ∼1 mm …

A Janus-Faced IM30 Ring Involved in Thylakoid Membrane Fusion Is Assembled from IM30 Tetramers.

2017

Summary Biogenesis and dynamics of thylakoid membranes likely involves membrane fusion events. Membrane attachment of the inner membrane-associated protein of 30 kDa (IM30) affects the structure of the lipid bilayer, finally resulting in membrane fusion. Yet, how IM30 triggers membrane fusion is largely unclear. IM30 monomers pre-assemble into stable tetrameric building blocks, which further align to form oligomeric ring structures, and differently sized IM30 rings bind to membranes. Based on a 3D reconstruction of IM30 rings, we locate the IM30 loop 2 region at the bottom of the ring and show intact membrane binding but missing fusogenic activity of loop 2 mutants. However, helix 7, which …

Direct Visualization of the Conformational Dynamics of Single Influenza Hemagglutinin Trimers

2018

Influenza hemagglutinin (HA) is the canonical type I viral envelope glycoprotein and provides a template for the membrane-fusion mechanisms of numerous viruses. The current model of HA-mediated membrane fusion describes a static "spring-loaded" fusion domain (HA2) at neutral pH. Acidic pH triggers a singular irreversible conformational rearrangement in HA2 that fuses viral and cellular membranes. Here, using single-molecule Förster resonance energy transfer (smFRET)-imaging, we directly visualized pH-triggered conformational changes of HA trimers on the viral surface. Our analyses reveal reversible exchange between the pre-fusion and two intermediate conformations of HA2. Acidification of p…

A Bimolecular Multicellular Complementation System for the Detection of Syncytium Formation: A New Methodology for the Identification of Nipah Virus …

2019

Fusion of viral and cellular membranes is a key step during the viral life cycle. Enveloped viruses trigger this process by means of specialized viral proteins expressed on their surface, the so-called viral fusion proteins. There are multiple assays to analyze the viral entry including those that focus on the cell-cell fusion induced by some viral proteins. These methods often rely on the identification of multinucleated cells (syncytium) as a result of cell membrane fusions. In this manuscript, we describe a novel methodology for the study of cell-cell fusion. Our approach, named Bimolecular Multicellular Complementation (BiMuC), provides an adjustable platform to qualitatively and quanti…

PspA adopts an ESCRT-III-like fold and remodels bacterial membranes

2021

Summary PspA is the main effector of the phage shock protein (Psp) system and preserves the bacterial inner membrane integrity and function. Here, we present the 3.6 A resolution cryoelectron microscopy (cryo-EM) structure of PspA assembled in helical rods. PspA monomers adopt a canonical ESCRT-III fold in an extended open conformation. PspA rods are capable of enclosing lipids and generating 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. Hotspots of these activities are zones derived from PspA assemblies, serving as lipid transfer platforms and lin…