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Nucleotide-binding domain and leucine-rich repeat pyrin-domain containing protein 1 (NLRP1) is an inflammasome sensor that mediates the activation of caspase-1 to induce cytokine maturation and pyroptosis 1 – 4 . Gain-of-function mutations of NLRP1 cause severe inflammatory diseases of the skin 4 – 6 . NLRP1 contains a function-to-find domain that auto-proteolyses into noncovalently associated subdomains 7 – 9 , and proteasomal degradation of the repressive N-terminal fragment of NLRP1 releases its inflammatory C-terminal fragment (NLRP1 CT) 10 , 11 . Cytosolic dipeptidyl peptidases 8 and 9 (hereafter, DPP8/DPP9) both interact with NLRP1, and small-molecule inhibitors of DPP8/DPP9 activate NLRP1 by mechanisms that are currently unclear 10 , 12 – 14 . Here we report cryo-electron microscopy structures of the human NLRP1–DPP9 complex alone and with Val-boroPro (VbP), an inhibitor of DPP8/DPP9. The structures reveal a ternary complex that comprises DPP9, full-length NLRP1 and the NLRPT CT. The binding of the NLRP1 CT to DPP9 requires full-length NLRP1, which suggests that NLRP1 activation is regulated by the ratio of NLRP1 CT to full-length NLRP1. Activation of the inflammasome by ectopic expression of the NLRP1 CT is consistently rescued by co-expression of autoproteolysis-deficient full-length NLRP1. The N terminus of the NLRP1 CT inserts into the DPP9 active site, and VbP disrupts this interaction. Thus, VbP weakens the NLRP1–DPP9 interaction and accelerates degradation of the N-terminal fragment 10 to induce inflammasome activation. Overall, these data demonstrate that DPP9 quenches low levels of NLRP1 CT and thus serves as a checkpoint for activation of the NLRP1 inflammasome. Structures of NLRP1–DPP9 alone and with a small-molecule inhibitor of DPP9 reveal the mechanisms through which NLRP1 is regulated, providing insights into the role of this complex in inflammasome regulation.

Modulation of voltage-gated potassium (Kv) channels by auxiliary subunits is central to the physiological function of channels in the brain and heart 1 , 2 . Native Kv4 tetrameric channels form macromolecular ternary complexes with two auxiliary β-subunits—intracellular Kv channel-interacting proteins (KChIPs) and transmembrane dipeptidyl peptidase-related proteins (DPPs)—to evoke rapidly activating and inactivating A-type currents, which prevent the backpropagation of action potentials 1 – 5 . However, the modulatory mechanisms of Kv4 channel complexes remain largely unknown. Here we report cryo-electron microscopy structures of the Kv4.2–DPP6S–KChIP1 dodecamer complex, the Kv4.2–KChIP1 and Kv4.2–DPP6S octamer complexes, and Kv4.2 alone. The structure of the Kv4.2–KChIP1 complex reveals that the intracellular N terminus of Kv4.2 interacts with its C terminus that extends from the S6 gating helix of the neighbouring Kv4.2 subunit. KChIP1 captures both the N and the C terminus of Kv4.2. In consequence, KChIP1 would prevent N-type inactivation and stabilize the S6 conformation to modulate gating of the S6 helices within the tetramer. By contrast, unlike the reported auxiliary subunits of voltage-gated channel complexes, DPP6S interacts with the S1 and S2 helices of the Kv4.2 voltage-sensing domain, which suggests that DPP6S stabilizes the conformation of the S1–S2 helices. DPP6S may therefore accelerate the voltage-dependent movement of the S4 helices. KChIP1 and DPP6S do not directly interact with each other in the Kv4.2–KChIP1–DPP6S ternary complex. Thus, our data suggest that two distinct modes of modulation contribute in an additive manner to evoke A-type currents from the native Kv4 macromolecular complex. Cryo-electron microscopy structures of the voltage-gated potassium channel Kv4.2 alone and in complex with auxiliary subunits (DPP6S and/or KChIP1) reveal the distinct mechanisms of these two different subunits in modulating channel activity.

Telomeres are protein–DNA complexes that protect chromosome ends from illicit ligation and resection. Telomerase is a ribonucleoprotein enzyme that synthesizes telomeric DNA to counter telomere shortening. Human telomeres are composed of complexes between telomeric DNA and a six-protein complex known as shelterin. The shelterin proteins TRF1 and TRF2 provide the binding affinity and specificity for double-stranded telomeric DNA, while the POT1-TPP1 shelterin subcomplex coats the single-stranded telomeric G-rich overhang that is characteristic of all our chromosome ends. By capping chromosome ends, shelterin protects telomeric DNA from unwanted degradation and end-to-end fusion events. Structures of the human shelterin proteins reveal a network of constitutive and context-specific interactions. The shelterin protein–DNA structures reveal the basis for both the high affinity and DNA sequence specificity of these interactions, and explain how shelterin efficiently protects chromosome ends from genome instability. Several protein–protein interactions, many provided by the shelterin component TIN2, are critical for upholding the end-protection function of shelterin. A survey of these protein–protein interfaces within shelterin reveals a series of “domain–peptide” interactions that allow for efficient binding and adaptability towards new functions. While the modular nature of shelterin has facilitated its part-by-part structural characterization, the interdependence of subunits within telomerase has made its structural solution more challenging. However, the exploitation of several homologs in combination with recent advancements in cryo-EM capabilities has led to an exponential increase in our knowledge of the structural biology underlying telomerase function. Telomerase homologs from a wide range of eukaryotes show a typical retroviral reverse transcriptase-like protein core reinforced with elements that deliver telomerase-specific functions including recruitment to telomeres and high telomere-repeat addition processivity. In addition to providing the template for reverse transcription, the RNA component of telomerase provides a scaffold for the catalytic and accessory protein subunits, defines the limits of the telomeric repeat sequence, and plays a critical role in RNP assembly, stability, and trafficking. While a high-resolution definition of the human telomerase structure is only beginning to emerge, the quick pace of technical progress forecasts imminent breakthroughs in this area. Here, we review the structural biology surrounding telomeres and telomerase to provide a molecular description of mammalian chromosome end protection and end replication.

Small-molecule inhibitors of the serine dipeptidases DPP8 and DPP9 (DPP8/9) induce a lytic form of cell death called pyroptosis in mouse and human monocytes and macrophages 1 , 2 . In mouse myeloid cells, Dpp8/9 inhibition activates the inflammasome sensor Nlrp1b, which in turn activates pro-caspase-1 to mediate cell death 3 , but the mechanism of DPP8/9 inhibitor-induced pyroptosis in human myeloid cells is not yet known. Here we show that the CARD-containing protein CARD8 mediates DPP8/9 inhibitor-induced pro-caspase-1-dependent pyroptosis in human myeloid cells. We further show that DPP8/9 inhibitors induce pyroptosis in the majority of human acute myeloid leukemia (AML) cell lines and primary AML samples, but not in cells from many other lineages, and that these inhibitors inhibit human AML progression in mouse models. Overall, this work identifies an activator of CARD8 in human cells and indicates that its activation by small-molecule DPP8/9 inhibitors represents a new potential therapeutic strategy for AML. Small-molecule inhibitors of the serine dipeptidases DPP8 and DPP9 block AML progression by promoting CARD8-dependent pyroptosis of leukemic myeloid cells.

Dipeptidyl Peptidase 9 (DPP9) is a prolyl amino dipeptidylpeptidase that can cut a post-proline peptide bond at the penultimate position at the N-terminus. By removing N-terminal prolines, this intracellular peptidase acts as an upstream regulator of the N-degron pathway. DPP9 has crucial roles in inflammatory regulation, DNA repair, cellular homeostasis, and cellular proliferation, while its deregulation is linked to cancer and immunological disorders. Currently, there is no fully selective chemical inhibitor and the DPP9 knockout transgenic mouse model is conditional. Mice and humans in which DPP9 catalytic activity is absent die neonatally. DPP9 inhibition for manipulating DPP9 activity in vivo has potential uses and there is rapid progress towards DPP9 selectivity, with 170x selectivity achieved. This review discusses roles of DPP9 in biology and diseases and potential applications of compounds that inhibit DPP9 and its related proteases.

Inhibitors of the post-proline-cleaving serine proteases DPP8 and DPP9 trigger a lytic form of programmed cell death called pyroptosis by activating pro-caspase-1 without autoproteolysis. Val-boroPro (Talabostat, PT-100), a nonselective inhibitor of post-proline cleaving serine proteases, stimulates mammalian immune systems through an unknown mechanism of action. Despite this lack of mechanistic understanding, Val-boroPro has attracted substantial interest as a potential anticancer agent, reaching phase 3 trials in humans. Here we show that Val-boroPro stimulates the immune system by triggering a proinflammatory form of cell death in monocytes and macrophages known as pyroptosis. We demonstrate that the inhibition of two serine proteases, DPP8 and DPP9, activates the pro-protein form of caspase-1 independent of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1β but does cleave and activate gasdermin D to induce pyroptosis. Mice lacking caspase-1 do not show immune stimulation after treatment with Val-boroPro. Our data identify what is to our knowledge the first small molecule that induces pyroptosis and reveals a new checkpoint that controls the activation of the innate immune system.

Telomeres are nucleoprotein complexes that play essential roles in protecting chromosome ends. Mammalian telomeres consist of repetitive DNA sequences bound by the shelterin complex. In this complex, the POT1-TPP1 heterodimer binds to single-stranded telomeric DNAs, while TRF1 and TRF2-RAP1 interact with double-stranded telomeric DNAs. TIN2, the linchpin of this complex, simultaneously interacts with TRF1, TRF2, and TPP1 to mediate the stable assembly of the shelterin complex. However, the molecular mechanism by which TIN2 interacts with these proteins to orchestrate telomere protection remains poorly understood. Here, we report the crystal structure of the N-terminal domain of TIN2 in complex with TIN2-binding motifs from TPP1 and TRF2, revealing how TIN2 interacts cooperatively with TPP1 and TRF2. Unexpectedly, TIN2 contains a telomeric repeat factor homology （TRFH）-Iike domain that functions as a protein-protein interaction platform. plays an important role in maintaining the stable shelterin Structure-based mutagenesis analyses suggest that TIN2 complex required for proper telomere end protection.

We have found multiple novel roles for voltage-gated potassium channel auxiliary subunit DPP6 (Dipeptidyl Peptidase-Like 6) including in neuronal development, learning and memory and connections to Alzheimer disease (AD)/dementia. Novel structures associated with amyloid-β (Aβ) were found in hippocampal area CA1 in aging DPP6-KO mice, apparently derived from degenerating presynaptic terminals, that are significantly more prevalent in DPP6-KO mice compared to WT mice. Aging DPP6-KO mice also show increased Aβ, tau pathologies, neuroinflammation and sleep disturbances. in vivo surgical implantation of the HD-X02 telemetry system (DSI) RESULT: The results showed twelve-month-old DPP6-KO mice have sleep disorders that include more wake and REM and less NREM duration in the light-on phase. For seizure study, aging DPP6-KO mice showed significantly increased and longer spike train durations, also exhibited a significantly higher prevalence of spike wave discharges and nonconvulsive seizures with no accompanying tonic-clonic movements compared to WT controls. We also found increase in the number of epileptiform spike events (over 400 mV) in 12-month-old DPP6-KO mice, and the epileptiform spike events were suppressed after acute administration of anti-seizure medicine levetiracetam (LEV) CONCLUSION: Together these results indicate that DPP6-KO mice have sleep disorders and seizure with epileptiform events, further supporting a role of DPP6 in Alzheimer's/dementia.

Canonical inflammasomes are innate immune signaling platforms that are formed in response to intracellular pathogen-associated signals and trigger caspase-1-dependent pyroptosis. Inflammasome formation and signaling is thought to mainly occur in myeloid cells, and in particular monocytes and macrophages. Here we show that small molecule inhibitors of dipeptidyl peptidases 8 and 9 (DPP8/9), which activate the related CARD8 and NLRP1 inflammasomes, also activate pyroptosis in human and rodent resting lymphocytes. We found that both CD4 + and CD8 + T cells were particularly sensitive to these inhibitors, although the sensitivity of T cells, like macrophages, varied considerably between species. In human T cells, we show that CARD8 mediates DPP8/9 inhibitor-induced pyroptosis. Intriguingly, although activated human T cells express the key proteins known to be required for CARD8-mediated pyroptosis, these cells were completely resistant to DPP8/9 inhibitors. Overall, these data show that resting lymphoid cells can activate at least one inflammasome, revealing additional cell types and states poised to undergo rapid pyroptotic cell death in response to danger-associated signals.

MicroRNAs (miRNAs) are essential regulators involved in multiple biological processes. To achieve their gene repression function, they are loaded in miRNA-specific Argonautes to form the miRNA-induced silencing complex (miRISC). Mammals and C. elegans possess more than one paralog of miRNA-specific Argonautes, but the dynamic between them remains unclear. Here, we report the conserved dipeptidyl peptidase DPF-3 as an interactor of the miRNA-specific Argonaute ALG-1 in C. elegans . Knockout of dpf-3 increases ALG-2 levels and miRISC formation in alg-1 loss-of-function animals, thereby compensating for ALG-1 loss and rescuing miRNA-related defects observed. DPF-3 can cleave an ALG-2 N-terminal peptide in vitro but does not appear to rely on this catalytic activity to regulate ALG-2 in vivo. This study uncovers the importance of DPF-3 in the miRNA pathway and provides insights into how multiple miRNA Argonautes contribute to achieving proper miRNA-mediated gene regulation in animals. Argonaute proteins are key effectors in the microRNA pathway. Here, the authors show that the conserved peptidase DPF-3 regulates Argonautes in C. elegans , and that loss of dpf-3 restores function and fitness in animals lacking the microRNA Argonaute ALG-1.