A missense mutation in the MLKL brace region promotes lethal neonatal inflammation and hematopoietic dysfunction.
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ABSTRACT:
SUBMITTER: Hildebrand JM
PROVIDER: S-EPMC7305203 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Necroptosis is a type of programmed cell death executed through the plasma membrane disruption by mixed lineage kinase domain-like protein (MLKL). Previous studies have revealed that an N-terminal four-helix bundle domain (NBD) of MLKL is the executioner domain for the membrane permeabilization, which is auto-inhibited by the first brace helix (H6). After necroptosis initiation, this inhibitory brace helix detaches and the NBD can integrate into the membrane, and hence leads to necroptotic cell death. However, how the NBD is released and induces membrane rupture is poorly understood. Here, we reconstituted MLKL2-154 into membrane mimetic bicelles and observed the structure disruption and membrane release of the first brace helix that is regulated by negatively charged phospholipids in a dose-dependent manner. Using molecular dynamics simulation we found that the brace region in an isolated, auto-inhibited MLKL2-154 becomes intrinsically disordered in solution after 7 ns dynamic motion. Further investigations demonstrated that a cluster of arginines in the C-terminus of MLKL2-154 is important for the molecular conformational switch. Functional mutagenesis showed that mutating these arginines to glutamates hindered the membrane disruption of full-length MLKL and thus inhibited the necroptotic cell death. These findings suggest that the brace helix also plays an active role in MLKL regulation, rather than an auto-inhibitory domain.
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Project description:Kindler Syndrome (KS), characterized by transient skin blistering followed by abnormal pigmentation, skin atrophy, and skin cancer, is caused by mutations in the FERMT1 gene. Although a few KS patients have been reported to also develop ulcerative colitis (UC), a causal link to the FERMT1 gene mutation is unknown. The FERMT1 gene product belongs to a family of focal adhesion proteins (Kindlin-1, -2, -3) that bind several beta integrin cytoplasmic domains. Here, we show that deleting Kindlin-1 in mice gives rise to skin atrophy and an intestinal epithelial dysfunction with similarities to human UC. This intestinal dysfunction results in perinatal lethality and is triggered by defective intestinal epithelial cell integrin activation, leading to detachment of this barrier followed by a destructive inflammatory response.
| S-EPMC2585060 | biostudies-literature
Project description:The programmed cell death pathway, necroptosis, relies on the pseudokinase, Mixed Lineage Kinase domain-Like (MLKL), for cellular execution downstream of death receptor or Toll-like receptor ligation. Receptor-interacting protein kinase-3 (RIPK3)-mediated phosphorylation of MLKL's pseudokinase domain leads to MLKL switching from an inert to activated state, where exposure of the N-terminal four-helix bundle (4HB) 'executioner' domain leads to cell death. The precise molecular details of MLKL activation, including the stoichiometry of oligomer assemblies, mechanisms of membrane translocation and permeabilisation, remain a matter of debate. Here, we dissect the function of the two 'brace' helices that connect the 4HB to the pseudokinase domain of MLKL. In addition to establishing that the integrity of the second brace helix is crucial for the assembly of mouse MLKL homotrimers and cell death, we implicate the brace helices as a device to communicate pseudokinase domain phosphorylation event(s) to the N-terminal executioner 4HB domain. Using mouse:human MLKL chimeras, we defined the first brace helix and adjacent loop as key elements of the molecular switch mechanism that relay pseudokinase domain phosphorylation to the activation of the 4HB domain killing activity. In addition, our chimera data revealed the importance of the pseudokinase domain in conferring host specificity on MLKL killing function, where fusion of the mouse pseudokinase domain converted the human 4HB + brace from inactive to a constitutive killer of mouse fibroblasts. These findings illustrate that the brace helices play an active role in MLKL regulation, rather than simply acting as a tether between the 4HB and pseudokinase domains.
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Project description:Complex I (NADH:ubiquinone oxidoreductase) is the first and largest multimeric complex of the mitochondrial respiratory chain. Human complex I comprises seven subunits encoded by mitochondrial DNA and 38 nuclear-encoded subunits that are assembled together in a process that is only partially understood. To date, mutations causing complex I deficiency have been described in all 14 core subunits, five supernumerary subunits, and four assembly factors. We describe complex I deficiency caused by mutation of the putative complex I assembly factor C20orf7. A candidate region for a lethal neonatal form of complex I deficiency was identified by homozygosity mapping of an Egyptian family with one affected child and two affected pregnancies predicted by enzyme-based prenatal diagnosis. The region was confirmed by microcell-mediated chromosome transfer, and 11 candidate genes encoding potential mitochondrial proteins were sequenced. A homozygous missense mutation in C20orf7 segregated with disease in the family. We show that C20orf7 is peripherally associated with the matrix face of the mitochondrial inner membrane and that silencing its expression with RNAi decreases complex I activity. C20orf7 patient fibroblasts showed an almost complete absence of complex I holoenzyme and were defective at an early stage of complex I assembly, but in a manner distinct from the assembly defects caused by mutations in the assembly factor NDUFAF1. Our results indicate that C20orf7 is crucial in the assembly of complex I and that mutations in C20orf7 cause mitochondrial disease.
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Project description:Rigidity and Multifocal Seizure Syndrome, Lethal Neonatal (RMFSL) (OMIM# 614498) is a rare and recently characterized epileptic encephalopathy that is related to variants in the BRAT1 gene (Breast Cancer 1-associated ataxia telangiectasia mutated activation-1 protein). In this report, an RMFSL case, who died in the 10th month of the life, with rigidity, drug-resistant myoclonic seizures in the face and extremities, with, significant motor delays is presented. The exon sequence was determined and a new homozygous variant (C.2230_2237dupAACATGC) was detected. This RMFSL case with a homozygous variant in the BRAT1 gene, is the fourth one in the literature and the first one being reported from a Turkish family.
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Project description:BackgroundsThe stimulator of interferon genes (STING) is an important driver in various inflammatory diseases.Methods and resultsHere, we have demonstrated that inhibition of RIPK3 and MLKL dampens STING signaling, indicating that necroptosis may be involved in sustaining STING signaling. Furthermore, RIPK3 knockout in HT-29 cells significantly suppressed STING signaling. Mechanistically, RIPK3 inhibits autophagic flux during STING activation. RIPK3 knockout inhibits STING signaling by intensifying STING autophagy. In contrast, MLKL regulates the STING pathway bidirectionally. MLKL deficiency enhances STING signaling, whereas suppression of MLKL-mediated pore formation restricts STING signaling. Mechanistically, upon abrogating the pro-necroptotic activity of MLKL, MLKL bound to activated STING is secreted to the extracellular space, where it restricts TBK1 and IRF3 recruitment. Targeting necroptotic signaling ameliorates STING activation during DMXAA-induced intestinal injury and sepsis.ConclusionsThese findings elucidate molecular mechanisms linking necroptosis to the STING pathway, and suggest a potential benefit of therapeutic targeting of necroptosis in STING-driven inflammatory diseases.
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Project description:Signaling molecule phosphatidylinositol 4,5-bisphosphate is produced primarily by phosphatidylinositol 4-phosphate 5-kinase (PIP5K). PIP5K is essential for the development of the human neuronal system, which has been exemplified by a recessive genetic disorder, lethal congenital contractural syndrome type 3, caused by a single aspartate-to-asparagine mutation in the kinase domain of PIP5Kγ. So far, the exact role of this aspartate residue has yet to be elucidated. In this work, we conducted structural, functional and computational studies on a zebrafish PIP5Kα variant with a mutation at the same site. Compared with the structure of the wild-type (WT) protein in the ATP-bound state, the ATP-associating glycine-rich loop of the mutant protein was severely disordered and the temperature factor of ATP was significantly higher. Both observations suggest a greater degree of disorder of the bound ATP, whereas neither the structure of the catalytic site nor the Km toward ATP was substantially affected by the mutation. Microsecond molecular dynamics simulation revealed that negative charge elimination caused by the mutation destabilized the involved hydrogen bonds and affected key electrostatic interactions in the close proximity of ATP. Taken together, our data indicated that the disease-related aspartate residue is a key node in the interaction network crucial for effective ATP binding. This work provides a paradigm of how a subtle but critical structural perturbation caused by a single mutation at the ATP-binding site abolishes the kinase activity, emphasizing that stabilizing substrate in a productive conformational state is crucial for catalysis.
| S-EPMC6434533 | biostudies-literature
Project description:Hypophosphatasia (HP) is a rare genetic disease caused by mutation in the alkaline phosphatase, liver/bone/kidney (ALPL) gene with highly variable clinical manifestations. Efforts have been made to collect cases with novel mutations and to examine how a missense mutation affects ALPL protein function, which remains difficult to predict. The present study investigated the underlying mechanism of ALPL dysfunction in a patient diagnosed with HP. Bidirectional sequencing of the ALPL gene was conducted in a 5‑year‑old Chinese girl preliminary diagnosed with childhood HP. Sorting Intolerant from Tolerant (SIFT) and Polymorphism Phenotyping v2 (PolyPhen‑2) tools were used to forecast the impact of the mutation on protein function. Site‑directed mutagenesis was performed and transfected into cells to verify the role of the specific mutation. Furthermore, the mechanism of the impact was investigated via all‑atom molecular dynamics (MD) simulation. The patient demonstrated a compound heterozygote with two missense mutations in the ALPL gene, p.Trp29Arg and p.Ile395Val. Trp29 and Ile395 were determined to be 'tolerable' by SIFT, whereas they were 'possibly damaging' by PolyPhen‑2 in terms of conservation. Additionally, HEK293 cells were transfected with plasmids expressing wild type and/or mutated ALPL. Only 4.1% of ALP activity remained when Trp29 was substituted by Arg, whereas 19.1, 33.7, 50.1 and 7.6% ALP activity remained in cells expressing p.Ile395Val, wild type+p.Trp29Arg, wild type+p.Ile395Val and p.Trp29Arg+p.Ile395Val substitutions, respectively. All‑atom MD simulation demonstrated that the N‑terminal helix of mutated ALPL, where Trp29 is located, separated from the main body of the protein after 30 nsec, and moved freely. These results demonstrated that p.Trp29Arg, as a novel missense mutation in the ALPL gene, reduced the enzymatic activity of ALPL. This effect may be associated with an uncontrolled N‑terminal helix. These results provide novel information about the genetic basis of HP, and may facilitate the development of future therapies.
| S-EPMC5482188 | biostudies-literature
Project description:RationalePolymerase subunit gamma (POLG) is a gene that codes for the catalytic subunit of the mitochondrial DNA polymerase, which is involved in the replication of mitochondrial DNA. Mutations in these genes are associated with a range of clinical syndromes characterized by secondary mtDNA defect including mtDNA mutation and mtDNA depletion which may culminate in complete failure of energy production (respiratory changes complex 1 defect) as in this case.Patient concernsWe herein report a full term Saudi female neonate born to consanguineous parents, who was noticed immediately after birth to have severe hypotonia, poor respiratory effort, and dysmorphic features. She had 3 siblings who died with same clinical scenario in neonatal period.DiagnosesMolecular genetic testing revealed a novel compound heterozygous mutation of POLG gene c.680G>A (p.Arg227Gin) and c.3098C>T (p.Ala1033Val).InterventionsThe patient remained in neonatal intensive care unit with multidisciplinary team management and was ventilator dependent until she passed away.OutcomesThe detected mutation had led to complete failure of energy production (respiratory changes complex 1 defect) until she died at the age of 5 months.LessonsMitochondrial respiratory chain defect should be considered in patients with severe neonatal hypotonia,encephalopathy, and respiratory failure especially in highly consanguineous population.
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Project description:Ptpn6 is a cytoplasmic phosphatase that functions to prevent autoimmune and interleukin-1 (IL-1) receptor-dependent, caspase-1-independent inflammatory disease. Conditional deletion of Ptpn6 in neutrophils (Ptpn6∆PMN) is sufficient to initiate IL-1 receptor-dependent cutaneous inflammatory disease, but the source of IL-1 and the mechanisms behind IL-1 release remain unclear. Here, we investigate the mechanisms controlling IL-1α/β release from neutrophils by inhibiting caspase-8-dependent apoptosis and Ripk1-Ripk3-Mlkl-regulated necroptosis. Loss of Ripk1 accelerated disease onset, whereas combined deletion of caspase-8 and either Ripk3 or Mlkl strongly protected Ptpn6∆PMN mice. Ptpn6∆PMN neutrophils displayed increased p38 mitogen-activated protein kinase-dependent Ripk1-independent IL-1 and tumor necrosis factor production, and were prone to cell death. Together, these data emphasize dual functions for Ptpn6 in the negative regulation of p38 mitogen-activated protein kinase activation to control tumor necrosis factor and IL-1α/β expression, and in maintaining Ripk1 function to prevent caspase-8- and Ripk3-Mlkl-dependent cell death and concomitant IL-1α/β release.
| S-EPMC6923591 | biostudies-literature