bims-mecosi 2023-09-10 papers

Issue of 2023–09–10
five papers selected by
Verena Kohler, University of Graz

EMBO Rep. 2023 Sep 08. e57758

Orchestrating vesicular and nonvesicular membrane dynamics by intrinsically disordered proteins.

Compartmentalization by membranes is a common feature of eukaryotic cells and serves to spatiotemporally confine biochemical reactions to control physiology. Membrane-bound organelles such as the endoplasmic reticulum (ER), the Golgi complex, endosomes and lysosomes, and the plasma membrane, continuously exchange material via vesicular carriers. In addition to vesicular trafficking entailing budding, fission, and fusion processes, organelles can form membrane contact sites (MCSs) that enable the nonvesicular exchange of lipids, ions, and metabolites, or the secretion of neurotransmitters via subsequent membrane fusion. Recent data suggest that biomolecule and information transfer via vesicular carriers and via MCSs share common organizational principles and are often mediated by proteins with intrinsically disordered regions (IDRs). Intrinsically disordered proteins (IDPs) can assemble via low-affinity, multivalent interactions to facilitate membrane tethering, deformation, fission, or fusion. Here, we review our current understanding of how IDPs drive the formation of multivalent protein assemblies and protein condensates to orchestrate vesicular and nonvesicular transport with a special focus on presynaptic neurotransmission. We further discuss how dysfunction of IDPs causes disease and outline perspectives for future research.

Keywords: intrinsically disordered proteins; membrane contact sites; neurotransmission; synapse; vesicular and nonvesicular transport

DOI: https://doi.org/10.15252/embr.202357758

mBio. 2023 Sep 07. e0094323

ER-dependent membrane repair of mycobacteria-induced vacuole damage.

Aby Anand, Anna-Carina Mazur, Patricia Rosell-Arevalo, Rico Franzkoch, Leonhard Breitsprecher, Stevanus A Listian, Sylvana V Hüttel, Danica Müller, Deise G Schäfer, Simone Vormittag, Hubert Hilbi, Markus Maniak, Maximiliano G Gutierrez, Caroline Barisch.

Several intracellular pathogens, such as Mycobacterium tuberculosis, damage endomembranes to access the cytosol and subvert innate immune responses. The host counteracts endomembrane damage by recruiting repair machineries that retain the pathogen inside the vacuole. Here, we show that the endoplasmic reticulum (ER)-Golgi protein oxysterol-binding protein (OSBP) and its Dictyostelium discoideum homolog OSBP8 are recruited to the Mycobacterium-containing vacuole (MCV) dependent on the presence of the ESX-1 secretion system, suggesting that their mobilization is associated with membrane damage. Lack of OSBP8 causes a hyperaccumulation of phosphatidylinositol-4-phosphate (PI4P) on the MCV and decreased cell viability. OSBP8-depleted cells had reduced lysosomal and degradative capabilities of their vacuoles that favored mycobacterial growth. In agreement with a potential role of OSBP8 in membrane repair, human macrophages infected with M. tuberculosis recruited OSBP in an ESX-1-dependent manner. These findings identified an ER-dependent repair mechanism for restoring MCVs in which OSBP8 functions to equilibrate PI4P levels on damaged membranes. IMPORTANCE Tuberculosis still remains a global burden and is one of the top infectious diseases from a single pathogen. Mycobacterium tuberculosis, the causative agent, has perfected many ways to replicate and persist within its host. While mycobacteria induce vacuole damage to evade the toxic environment and eventually escape into the cytosol, the host recruits repair machineries to restore the MCV membrane. However, how lipids are delivered for membrane repair is poorly understood. Using advanced fluorescence imaging and volumetric correlative approaches, we demonstrate that this involves the recruitment of the endoplasmic reticulum (ER)-Golgi lipid transfer protein OSBP8 in the Dictyostelium discoideum/Mycobacterium marinum system. Strikingly, depletion of OSBP8 affects lysosomal function accelerating mycobacterial growth. This indicates that an ER-dependent repair pathway constitutes a host defense mechanism against intracellular pathogens such as M. tuberculosis.

Keywords: Dictyostelium discoideum; Mycobacterium marinum; Mycobacterium tuberculosis; Sac1; lysosome; macrophages; membrane contact site; membrane repair; oxysterol-binding protein; phosphatidylinositol 4-phosphate; sterol

DOI: https://doi.org/10.1128/mbio.00943-23

Nat Commun. 2023 Sep 02. 14(1): 5343

MAVS integrates glucose metabolism and RIG-I-like receptor signaling.

MAVS is an adapter protein involved in RIG-I-like receptor (RLR) signaling in mitochondria, peroxisomes, and mitochondria-associated ER membranes (MAMs). However, the role of MAVS in glucose metabolism and RLR signaling cross-regulation and how these signaling pathways are coordinated among these organelles have not been defined. This study reports that RLR action drives a switch from glycolysis to the pentose phosphate pathway (PPP) and the hexosamine biosynthesis pathway (HBP) through MAVS. We show that peroxisomal MAVS is responsible for glucose flux shift into PPP and type III interferon (IFN) expression, whereas MAMs-located MAVS is responsible for glucose flux shift into HBP and type I IFN expression. Mechanistically, peroxisomal MAVS interacts with G6PD and the MAVS signalosome forms at peroxisomes by recruiting TNF receptor-associated factor 6 (TRAF6) and interferon regulatory factor 1 (IRF1). By contrast, MAMs-located MAVS interact with glutamine-fructose-6-phosphate transaminase, and the MAVS signalosome forms at MAMs by recruiting TRAF6 and TRAF2. Our findings suggest that MAVS mediates the interaction of RLR signaling and glucose metabolism.

DOI: https://doi.org/10.1038/s41467-023-41028-9

Plant Physiol. 2023 Sep 05. pii: kiad489. [Epub ahead of print]

Arabidopsis MCTP family member QUIRKY regulates the formation of the STRUBBELIG receptor kinase complex.

Xia Chen, Barbara Leśniewska, Rodion Boikine, Nicole Yun, Tejasvinee Atul Mody, Prasad Vaddepalli, Kay Schneitz.

Intercellular communication plays a central role in organogenesis. Tissue morphogenesis in Arabidopsis (Arabidopsis thaliana) requires signaling mediated by a cell surface complex containing the atypical receptor kinase STRUBBELIG (SUB) and the multiple C2 domains and transmembrane region protein QUIRKY (QKY). QKY is required to stabilize SUB at the plasma membrane. However, it is unclear what the in vivo architecture of the QKY/SUB signaling complex is, how it is controlled, and how it relates to the maintenance of SUB at the cell surface. We addressed these questions using a combination of genetics, yeast two-hybrid assays and Förster resonance energy transfer (FRET)/fluorescence lifetime imaging microscopy (FLIM) in epidermal cells of seedling roots. We found that QKY promotes the formation of SUB homo-oligomers in vivo. Homo-oligomerization of SUB appeared to involve its extracellular domain. We also showed that QKY and SUB physically interact and form a complex at the cell surface in vivo. In addition, the data showed that the N-terminal C2A-B region of QKY interacts with the intracellular domain of SUB. They further revealed that this interaction is essential to maintain SUB levels at the cell surface. Finally, we provided evidence that QKY forms homo-multimers in vivo in a SUB-independent manner. We suggest a model in which the physical interaction of QKY with SUB mediates the oligomerization of SUB and attenuates its internalization, thereby maintaining sufficiently high levels of SUB at the cell surface required for the control of tissue morphogenesis.

Keywords: intercellular communication in plants; membrane contact sites; multiple C2 domain and transmembrane region proteins; plasmodesmata

DOI: https://doi.org/10.1093/plphys/kiad489

Mov Disord. 2023 Sep 05.

An Autopsy Series of Seven Cases of VPS13A Disease (Chorea-Acanthocytosis).

BACKGROUND: Vacuolar protein sorting 13 homolog A (VPS13A) disease, historically known as chorea-acanthocytosis, is a rare neurodegenerative disorder caused by biallelic mutations in VPS13A, usually resulting in reduced or absent levels of its protein product, VPS13A. VPS13A localizes to contact sites between subcellular organelles, consistent with its recently identified role in lipid transfer between membranes. Mutations are associated with neuronal loss in the striatum, most prominently in the caudate nucleus, and associated marked astrogliosis. There are no other known disease-specific cellular changes (eg, protein aggregation), but autopsy reports to date have been limited, often lacking genetic or biochemical diagnostic confirmation.
OBJECTIVE: The goal of this study was to characterize neuropathological findings in the brains of seven patients with VPS13A disease (chorea-acanthocytosis).
METHODS: In this study, we collected brain tissues and clinical data from seven cases of VPS13A for neuropathological analysis. The clinical diagnosis was confirmed by the presence of VPS13A mutations and/or immunoblot showing the loss or reduction of VPS13A protein. Tissues underwent routine, special, and immunohistochemical staining focused on neurodegeneration. Electron microscopy was performed in one case.
RESULTS: Gross examination showed severe striatal atrophy. Microscopically, there was neuronal loss and astrogliosis in affected regions. Luxol fast blue staining showed variable lipid accumulation with diverse morphology, which was further characterized by electron microscopy. In some cases, rare degenerating p62- and ubiquitin-positive cells were present in affected regions. Calcifications were present in four cases, being extensive in one.
CONCLUSIONS: We present the largest autopsy series of biochemically and genetically confirmed VPS13A disease and identify novel histopathological findings implicating abnormal lipid accumulation. © 2023 International Parkinson and Movement Disorder Society.

Keywords: VPS13A; chorea-acanthocytosis; lipid; neuroacanthocytosis; neuropathology

DOI: https://doi.org/10.1002/mds.29589