Quasi-periodic eruptions (QPEs) are luminous bursts of soft X-rays from the nuclei of galaxies, repeating on timescales of hours to weeks. The mechanism behind these rare systems is uncertain, but most theories involve accretion disks around supermassive black holes (SMBHs) undergoing instabilities or interacting with a stellar object in a close orbit. It has been suggested that this disk could be created when the SMBH disrupts a passing star, implying that many QPEs should be preceded by observable tidal disruption events (TDEs).
View Article and Find Full Text PDFThe protein scaffold that includes the caspases is ancient and found in all domains of life. However, the stringent specificity that defines the caspase biologic function is relatively recent and found only in multicellular animals. During the radiation of the Chordata, members of the caspase family adopted roles in immunity, events coinciding with the development of substrates that define the modern innate immune response.
View Article and Find Full Text PDFMany proinflammatory proteins are released via the necrotic form of cell death known as pyroptosis. Sometimes known as gasdermin D (GSDMD) dependent cell death, pyroptosis results from the formation of pores in the plasma membrane leading to eventual cell lysis. Seeking to understand the magnitude of this cell lysis we measured the size of proteins released during pyroptosis.
View Article and Find Full Text PDFPurpose: Retinal vein occlusion (RVO) is a sight-threatening condition typically treated with intravitreal injection of vascular endothelial growth factor (VEGF) antagonists. Treatment response to anti-VEGF therapies is highly variable, with poor visual outcomes and treatment response in patients with significant retinal nonperfusion following RVO. Recently, caspase-9 has been identified as a potent regulator of edema, gliosis, and neuronal dysfunction during acute retinal hypoxia.
View Article and Find Full Text PDFNecroptosis is a form of regulated cell death triggered by various host and pathogen-derived molecules during infection and inflammation. The essential step leading to necroptosis is phosphorylation of the mixed lineage kinase domain-like protein by receptor-interacting protein kinase 3. Caspase-8 cleaves receptor-interacting protein kinases to block necroptosis, so synthetic caspase inhibitors are required to study this process in experimental models.
View Article and Find Full Text PDFA patient diagnosed with multiple myeloma, bicuspid aortic valve, and Von Hippel-Lindau syndrome underwent whole-exome sequencing seeking a unified genetic cause for these three pathologies. The patient possessed a single-point mutation of arginine to cysteine (R24C) in the N-terminal region(pro-domain) of matrix metalloproteinase 9 (MMP-9). The pro-domain interacts with the catalytic site of this enzyme rendering it inactive.
View Article and Find Full Text PDFPyroptosis is a mechanism of inflammatory cell death mediated by the activation of the prolytic protein gasdermin D by caspase-1, caspase-4, and caspase-5 in human, and caspase-1 and caspase-11 in mouse. In addition, caspase-1 amplifies inflammation by proteolytic activation of cytokine interleukin-1β (IL-1β). Modern mammals of the order Carnivora lack the caspase-1 catalytic domain but express an unusual version of caspase-4 that can activate both gasdermin D and IL-1β.
View Article and Find Full Text PDFRegulated cell death is defined as genetically encoded pathways that lead towards the demise of cells. In mammals, cell demise can be either inflammatory or non-inflammatory, depending on whether the mechanism of death results in cell rupture or not. Inflammatory cell death can lead towards acute and chronic disease.
View Article and Find Full Text PDFCaspases are a family of enzymes that play roles in cell death and inflammation. It has been suggested that in the execution phase of the apoptotic pathway, caspase-3, -6 and -7 are involved. The substrate specificities of two proteases (caspases 3 and 7) are highly similar, which complicates the design of compounds that selectively interact with a single enzyme exclusively.
View Article and Find Full Text PDFAza-peptide aldehydes and ketones are a new class of reversible protease inhibitors that are specific for the proteasome and clan CD cysteine proteases. We designed and synthesised aza-Leu derivatives that were specific for the chymotrypsin-like active site of the proteasome, aza-Asp derivatives that were effective inhibitors of caspases-3 and -6, and aza-Asn derivatives that inhibited and legumains. The crystal structure of caspase-3 in complex with our caspase-specific aza-peptide methyl ketone inhibitor with an aza-Asp residue at P1 revealed a covalent linkage between the inhibitor carbonyl carbon and the active site cysteinyl sulphur.
View Article and Find Full Text PDFMany proteases recognize their substrates with high specificities, with this in mind, it should theoretically be possible to utilize the substrate binding cleft of a protease as a scaffold to engineer an affinity reagent. In this study, we sought to develop reagents that would differentiate between substrates and products of proteolysis, based on a caspase 7 scaffold. Firstly, we engineered a form of caspase 7 that can undergo conversion to a substrate binding conformation without catalysis.
View Article and Find Full Text PDFCentral nervous system ischemic injury features neuronal dysfunction, inflammation and breakdown of vascular integrity. Here we show that activation of endothelial caspase-9 after hypoxia-ischemia is a critical event in subsequent dysfunction of the blood-retina barrier, using a panel of interrelated ophthalmic in vivo imaging measures in a mouse model of retinal vein occlusion (RVO). Rapid nonapoptotic activation of caspase-9 and its downstream effector caspase-7 in endothelial cells promotes capillary ischemia and retinal neurodegeneration.
View Article and Find Full Text PDFPyroptosis is the caspase-dependent inflammatory cell death mechanism that underpins the innate immune response against pathogens and is dysregulated in inflammatory disorders. Pyroptosis occurs via two pathways: the canonical pathway, signaled by caspase-1, and the noncanonical pathway, regulated by mouse caspase-11 and human caspase-4/5. All inflammatory caspases activate the pyroptosis effector protein gasdermin D, but caspase-1 mostly activates the inflammatory cytokine precursors prointerleukin-18 and prointerleukin-1β (pro-IL18/pro-IL1β).
View Article and Find Full Text PDFNatural killer (NK) cells are key innate immunity effectors that combat viral infections and control several cancer types. For their immune function, human NK cells rely largely on five different cytotoxic proteases, called granzymes (A/B/H/K/M). Granzyme B (GrB) initiates at least three distinct cell death pathways, but key aspects of its function remain unexplored because selective probes that detect its activity are currently lacking.
View Article and Find Full Text PDFGenetic polymorphisms in the region of the trimeric serine hydrolase high-temperature requirement 1 () are associated with increased risk of age-related macular degeneration (AMD) and disease progression, but the precise biological function of HtrA1 in the eye and its contribution to disease etiologies remain undefined. In this study, we have developed an HtrA1-blocking Fab fragment to test the therapeutic hypothesis that HtrA1 protease activity is involved in the progression of AMD. Next, we generated an activity-based small-molecule probe (ABP) to track target engagement in vivo.
View Article and Find Full Text PDFMetacaspases and paracaspases are proteases that were first identified as containing a caspase-like structural fold (Uren et al., 2000). Like caspases, meta- and paracaspases are multifunctional proteins regulating diverse biological phenomena, such as aging, immunity, proteostasis and programmed cell death.
View Article and Find Full Text PDFCytotoxic T-lymphocytes (CTLs) and natural killer cells (NKs) kill compromised cells to defend against tumor and viral infections. Both effector cell types use multiple strategies to induce target cell death including Fas/CD95 activation and the release of perforin and a group of lymphocyte granule serine proteases called granzymes. Granzymes have relatively broad and overlapping substrate specificities and may hydrolyze a wide range of peptidic epitopes; it is therefore challenging to identify their natural and synthetic substrates and to distinguish their localization and functions.
View Article and Find Full Text PDFSince their discovery, the matrix metalloproteinase (MMP) family proteases have been considered as therapeutic targets in numerous diseases and disorders. Unfortunately, clinical trials with MMP inhibitors have failed to yield any clinical benefits of these inhibitors. These failures were largely due to a lack of MMP-selective agents; accordingly, it has become important to identify a platform with which high selectivity can be achieved.
View Article and Find Full Text PDFThe cytosolic appearance and propagation of bacteria cause overwhelming cellular stress responses that induce apoptosis under normal conditions. Therefore, successful bacterial colonization depends on the ability of intracellular pathogens to block apoptosis and to safeguard bacterial replicative niches. Here, we show that the cytosolic Gram-negative bacterium Shigella flexneri stalls apoptosis by inhibiting effector caspase activity.
View Article and Find Full Text PDFHuman cysteine cathepsins constitute an 11-membered family of proteases responsible for degradation of proteins in cellular endosomal-lysosomal compartments as such, they play important roles in antigen processing, cellular stress signaling, autophagy, and senescence. Moreover, for many years these enzymes were also linked to tumor growth, invasion, angiogenesis and metastasis when upregulated. Individual biological roles of each cathepsin are difficult to establish, because of their redundancy and similar substrate specificities.
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