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 has recently been shown to mediate membrane binding, was located at the oppossite, top side of IM30 rings. We propose that a two-sided IM30 ring complex connects two opposing membranes, finally resulting in membrane fusion. Thus, IM30-mediated membrane fusion requires a Janus-faced IM30 ring.
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•IM30 monomers assemble into stable tetrameric building blocks prior to ring formation•3D reconstructions of different IM30 rings are presented•Helix 7 and loop 2 are located at opposite sides of IM30 rings•IM30-mediated membrane fusion requires a Janus-faced IM30 ring
The IM30 protein is a membrane fusion protein that forms large oligomeric rings from tetrameric building blocks. Saur et al. present 3D reconstructions of the Janus-faced IM30 ring, which illustrates membrane binding properties as well as the membrane fusion activity of IM30.
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 Å 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 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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•Cryo-EM structure of assembled helical PspA rods•PspA adopts a canonical ESCRT-III fold•PspA rods can enclose lipids generating positive membrane curvature•PspA remodels bacterial membranes following fusion and fission events
Structural and functional characterization of PspA reveals an unkown ESCRT-III family member capable of mediating membrane fission and fusion processes.
The thylakoid membrane of chloroplasts and cyanobacteria is a unique internal membrane system harbouring the complexes of the photosynthetic electron transfer chain. Despite their apparent ...importance, little is known about the biogenesis and maintenance of thylakoid membranes. Although membrane fusion events are essential for the formation of thylakoid membranes, proteins involved in membrane fusion have yet to be identified in photosynthetic cells or organelles. Here we show that IM30, a conserved chloroplast and cyanobacterial protein of approximately 30 kDa binds as an oligomeric ring in a well-defined geometry specifically to membranes containing anionic lipids. Triggered by Mg(2+), membrane binding causes destabilization and eventually results in membrane fusion. We propose that IM30 establishes contacts between internal membrane sites and promotes fusion to enable regulated exchange of proteins and/or lipids in cyanobacteria and chloroplasts.
As a key feature in oxygenic photosynthesis, thylakoid membranes play an essential role in the physiology of plants, algae, and cyanobacteria. Despite their importance in the process of oxygenic ...photosynthesis, their biogenesis has remained a mystery to the present day. A decade ago, vesicle-inducing protein in plastids 1 (Vipp1) was described to be involved in thylakoid membrane formation in chloroplasts and cyanobacteria. Most follow-up studies clearly linked Vipp1 to membranes and Vipp1 interactions as well as the defects observed after Vipp1 depletion in chloroplasts and cyanobacteria indicate that Vipp1 directly binds to membranes, locally stabilizes bilayer structures, and thereby retains membrane integrity. Here current knowledge about the structure and function of Vipp1 is summarized with a special focus on its relationship to the bacterial phage shock protein A (PspA), as both proteins share a common origin and appear to have retained many similarities in structure and function.
The IM30 (inner membrane-associated protein of 30 kDa), also known as the Vipp1 (vesicle-inducing protein in plastids 1), has a crucial role in thylakoid membrane biogenesis and maintenance. Recent ...results suggest that the protein binds peripherally to membranes containing negatively charged lipids. However, although IM30 monomers interact and assemble into large oligomeric ring complexes with different numbers of monomers, it is still an open question whether ring formation is crucial for membrane interaction. Here we show that binding of IM30 rings to negatively charged phosphatidylglycerol membrane surfaces results in a higher ordered membrane state, both in the head group and in the inner core region of the lipid bilayer. Furthermore, by using gold nanorods covered with phosphatidylglycerol layers and single particle spectroscopy, we show that not only IM30 rings but also lower oligomeric IM30 structures interact with membranes, although with higher affinity. Thus, ring formation is not crucial for, and even counteracts, membrane interaction of IM30.
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 contrast, the IM30 C-terminal domain is involved in and necessary to stabilize defined contacts to negatively charged membrane surfaces, and to modulate the IM30-induced membrane fusion activity. Although the two IM30 protein domains have distinct functional roles, only together they enable IM30 to work properly.
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•The IM30 C-terminus does not affect the structure and stability of IM30.•Membrane binding of IM30 involves the PspA- as well as the C-terminal domain.•The IM30 C-terminus interacts with negatively charged membrane surfaces.•Charged residues inside the IM30 C-terminus influence stability of membrane binding.•Membrane binding of the IM30 C-terminus correlates with the proteins fusogenic activity.
Vipp1: a very important protein in plastids? VOTHKNECHT, Ute C; OTTERS, Stephanie; HENNIG, Raoul ...
Journal of experimental botany,
2012, Letnik:
63, Številka:
4
Journal Article
Real-time multisensory social interactions (RMSIs) between people are at the center of the metaverse, a new computer-mediated environment consisting of virtual “worlds” in which people act and ...communicate with each other in real-time via avatars. This research investigates whether RMSIs in the metaverse, when accessed through virtual-reality headsets, can generate more value for interactants in terms of interaction outcomes (interaction performance, evaluation, and emotional responses) than those on the two-dimensional (2D) internet (e.g., Zoom meetings). We combine theoretical logic with extensive field-experimental probes (which support the value-creation potential of the virtual-reality metaverse, but contradict its
general
superiority) to develop and refine a framework of how RMSIs in the metaverse versus on the 2D internet affect interaction outcomes through interactants’ intermediate conditions. The refined framework serves as foundation for a research roadmap on RMSIs in the metaverse, in which we highlight the critical roles of specific mediating and moderating forces along with interactional formats for future investigations of the metaverse and also name key business areas and societal challenges that deserve scholarly attention.
Managers frequently seek strategies to profit systematically from social media to increase product sales. By forming a brand alliance, they can acquire an installed social media base from a partner ...brand in an attempt to boost the sales of their composite products. Drawing from power theory, this article develops a conceptual model of the influence of the social media power of partner brands on brand alliance success. The proposed framework details the partner brand's social media power potential (size and activity of the social media network), social media power exertion (different posting behaviors and comments), and their interaction. The authors test this framework with an extensive data set from the film industry, in which films function as composite products and actors represent partner brands. The data set features 442 movies, including 1,318 actor-movie combinations and weekly social media data (including 41,547 coded Facebook posts). The authors apply a linear mixed-effects model, in which they account for endogeneity concerns. The partner brand's social media power potential, power exertion, and their interaction can all lead to higher composite product sales. By coding different types of product-related posts, this article provides estimates of their varying monetary value.
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