The voltage-dependent anion channel (VDAC) mediates trafficking of small molecules and ions across the eukaryotic outer mitochondrial membrane. VDAC also interacts with anti-apoptotic proteins from the Bcl-2 family and this interaction inhibits release of apoptogenic proteins from the mitochondrion. We present the NMR solution structure of recombinant human VDAC-1 reconstituted in detergent micelles. It forms a 19-stranded β-barrel with the first and last strand parallel. The hydrophobic outside perimeter of the barrel is covered by detergent molecules in a belt-like fashion. In the presence of cholesterol recombinant VDAC-1 can form voltage-gated channels in phospholipid bilayers similar to the native protein. NMR measurements revealed the binding sites of VDAC-1 for the Bcl-2 protein Bcl-xL, for β-NADH and for cholesterol. Bcl-xL interacts with the VDAC barrel laterally at strands 17 and 18.

Pyroptosis is a lytic type of cell death that is initiated by inflammatory caspases. These caspases are activated within multi‐protein inflammasome complexes that assemble in response to pathogens and endogenous danger signals. Pyroptotic cell death has been proposed to proceed via the formation of a plasma membrane pore, but the underlying molecular mechanism has remained unclear. Recently, gasdermin D (GSDMD), a member of the ill‐characterized gasdermin protein family, was identified as a caspase substrate and an essential mediator of pyroptosis. GSDMD is thus a candidate for pyroptotic pore formation. Here, we characterize GSDMD function in live cells and in vitro. We show that the N‐terminal fragment of caspase‐1‐cleaved GSDMD rapidly targets the membrane fraction of macrophages and that it induces the formation of a plasma membrane pore. In vitro, the N‐terminal fragment of caspase‐1‐cleaved recombinant GSDMD tightly binds liposomes and forms large permeability pores. Visualization of liposome‐inserted GSDMD at nanometer resolution by cryo‐electron and atomic force microscopy shows circular pores with variable ring diameters around 20 nm. Overall, these data demonstrate that GSDMD is the direct and final executor of pyroptotic cell death.

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Inflammasome complexes function as key innate immune effectors that trigger inflammation in response to pathogen- and danger-associated signals. Here, we report that germline mutations in the inflammasome sensor NLRP1 cause two overlapping skin disorders: multiple self-healing palmoplantar carcinoma (MSPC) and familial keratosis lichenoides chronica (FKLC). We find that NLRP1 is the most prominent inflammasome sensor in human skin, and all pathogenic NLRP1 mutations are gain-of-function alleles that predispose to inflammasome activation. Mechanistically, NLRP1 mutations lead to increased self-oligomerization by disrupting the PYD and LRR domains, which are essential in maintaining NLRP1 as an inactive monomer. Primary keratinocytes from patients experience spontaneous inflammasome activation and paracrine IL-1 signaling, which is sufficient to cause skin inflammation and epidermal hyperplasia. Our findings establish a group of non-fever inflammasome disorders, uncover an unexpected auto-inhibitory function for the pyrin domain, and provide the first genetic evidence linking NLRP1 to skin inflammatory syndromes and skin cancer predisposition.

A hallmark of inflammasome activation is the ASC speck, a micrometre-sized structure formed by the inflammasome adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD), which consists of a pyrin domain (PYD) and a caspase recruitment domain (CARD). Here we show that assembly of the ASC speck involves oligomerization of ASCPYD into filaments and cross-linking of these filaments by ASCCARD. ASC mutants with a non-functional CARD only assemble filaments but not specks, and moreover disrupt endogenous specks in primary macrophages. Systematic site-directed mutagenesis of ASCPYD is used to identify oligomerization-deficient ASC mutants and demonstrate that ASC speck formation is required for efficient processing of IL-1β, but dispensable for gasdermin-D cleavage and pyroptosis induction. Our results suggest that the oligomerization of ASC creates a multitude of potential caspase-1 activation sites, thus serving as a signal amplification mechanism for inflammasome-mediated cytokine production.

Neurodegeneration in Parkinson's disease is correlated with the occurrence of Lewy bodies, intracellular inclusions containing aggregates of the intrinsically disordered protein (IDP) α-Synuclein 1 . The aggregation propensity of α-Synuclein in cells is modulated by specific factors including posttranslational modifications 2,3 , Abelson-kinase-mediated phosphorylation 4,5 and interactions with intracellular machineries such as molecular chaperones, although the underlying mechanisms are unclear [6][7][8] . Here, we systematically characterize the interaction of molecular chaperones with α-Synuclein in vitro as well as in cells at the atomic level. We find that six vastly different molecular chaperones commonly recognize a canonical motif in α-Synuclein, consisting Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms *

The pro-inflammatory cytokine IL-1β is well known for its role in host defense and the initiation of potent inflammatory responses. It is processed from its inactive pro-form by the inflammatory caspase-1 into its mature bioactive form, which is then released from the cell via an unconventional secretion mechanism. Recently, gasdermin-D has been identified as a new target of caspase-1. After proteolytical cleavage of gasdermin-D, the N-terminal fragment induces pyroptosis, a lytic cell death, by forming large permeability pores in the plasma membrane. Here we show using the murine system that gasdermin-D is required for IL-1β secretion by macrophages, dendritic cells and partially in neutrophils, and that secretion is a cell-lysis-independent event. Liposome transport assays in vitro further demonstrate that gasdermin-D pores are large enough to allow the direct release of IL-1β. Moreover, IL-18 and other small soluble cytosolic proteins can also be released in a lysis-independent but gasdermin-D-dependent mode, suggesting that the gasdermin-D pores allow passive the release of cytosolic proteins in a size-dependent manner.

The biogenesis of integral outer-membrane proteins (OMPs) in Gram-negative bacteria requires molecular chaperones that prevent the aggregation of OMP polypeptides in the aqueous periplasmic space. How these energy-independent chaperones interact with their substrates is not well understood. We have used high-resolution NMR spectroscopy to examine the conformation and dynamics of the Escherichia coli periplasmic chaperone Skp and two of its complexes with OMPs. The Skp trimer constitutes a flexible architectural scaffold that becomes more rigid upon substrate binding. The OMP substrates populate a dynamic conformational ensemble with structural interconversion rates on the submillisecond timescale. The global lifetime of the chaperone-substrate complex is seven orders of magnitude longer, emerging from the short local lifetimes by avidity. The dynamic state allows for energy-independent substrate release and provides a general paradigm for the conformation of OMP polypeptides bound to energy-independent chaperones.