Plasma membrane rupture (PMR) is the final cataclysmic event in lytic cell death. PMR releases intracellular molecules termed damage-associated molecular patterns (DAMPs) that propagate the inflammatory response. The underlying mechanism for PMR, however, is unknown. Here we show that the ill-characterized nerve injury-induced protein 1 (NINJ1) -a cell surface protein with two transmembrane regions -plays an essential role in the induction of PMR. A forward-genetic screen of randomly mutagenized mice linked NINJ1 to PMR. Ninj1 -/macrophages exhibited impaired PMR in response to diverse inducers of pyroptotic, necrotic and apoptotic cell death, and failed to release numerous intracellular proteins including High Mobility Group Box 1 (HMGB1, a known DAMP) and Lactate Dehydrogenase (LDH, a standard measure of PMR). Ninj1 -/macrophages died, but with a distinctive and persistent ballooned morphology, attributable to defective disintegration of bubble-like herniations. Ninj1 -/mice were more susceptible than wildtype mice to Citrobacter rodentium, suggesting a role for PMR in anti-bacterial host defense.Mechanistically, NINJ1 utilized an evolutionarily conserved extracellular α-helical domain for oligomerization and subsequent PMR. The discovery of NINJ1 as a mediator of PMR overturns the long-held dogma that cell death-related PMR is a passive event.Pyroptosis is a potent inflammatory mode of lytic cell death triggered by diverse infectious and sterile insults 1-3 . It is driven by the pore-forming fragment of gasdermin D (GSDMD) 4-7 and releases two exemplar proteins: interleukin-1β (IL-1β), a pro-inflammatory cytokine, and LDH, a standard marker of PMR and lytic cell death. An early landmark study 8 predicted two sequential steps for pyroptosis: (1) initial formation of a small plasma membrane pore causing IL-1β release and non-selective ionic fluxes, and (2) subsequent PMR attributable to oncotic cell swelling. PMR releases LDH (140 kDa) and large DAMPs. While the predicted size of gasdermin pores (~18 nm inner diameter 9 ) is large enough to release IL-1β (17 kDa, ~4.5 nm diameter), the underlying mechanism for subsequent PMR has been considered a passive osmotic lysis event. An unbiased forward genetic screen identifies NINJ1To identify essential mediators of PMR, we performed a forward genetic screen using bone marrow-derived macrophages (BMDMs) from N-ethyl-N-nitrosourea (ENU)-mutagenized mice.

Inorganic manganese based particles are becoming attractive for molecular and cellular imaging, due to their ability to provide bright contrast on MRI, as opposed to the dark contrast generated from iron based particles. Using a single emulsion technique, we have successfully fabricated pH sensitive, poly(lactic-co-glycolic acid) (PLGA) encapsulated manganese oxide (MnO) nanocrystals. Two classes of particles were fabricated at ~ 140 nm and 1.7 μm, and incorporated 15 to 20 nm MnO nanocrystals with high encapsulation efficiencies. Intact particles at physiological pH cause little contrast in MRI, but following endocytosis into low pH compartments within the cells, the particles erode, and MnO dissolves to release Mn2+. This causes the cells to appear bright on MR images. The magnitude of the change in MRI properties is as high as 35-fold, making it the most dynamic ‘smart’ MRI contrast agent yet reported. Possible applications of these MnO particles include slow release Mn2+, tumor targeting, and confirmation of cell uptake.

Enzymes use binding energy to stabilize their substrates in high-energy states that are otherwise inaccessible at ambient temperature. Here we show that a de novo designed Zn(ii) metalloprotein stabilizes a chemically reactive organic radical that is otherwise unstable in aqueous media. The protein binds tightly to and stabilizes the radical semiquinone form of 3,5-di-tert-butylcatechol. Solution NMR spectroscopy in conjunction with molecular dynamics simulations show that the substrate binds in the active site pocket where it is stabilized by metal–ligand interactions as well as by burial of its hydrophobic groups. Spectrochemical redox titrations show that the protein stabilized the semiquinone by reducing the electrochemical midpoint potential for its formation via the one-electron oxidation of the catechol by approximately 400 mV (9 kcal mol−1). Therefore, the inherent chemical properties of the radical were changed drastically by harnessing its binding energy to the metalloprotein. This model sets the basis for designed enzymes with radical cofactors to tackle challenging chemistry.

Ferroptosis is a form of programmed cell death associated with inflammation, neurodegeneration, and ischemia. Vitamin E (alpha-tocopherol) has been reported to prevent ferroptosis, but the mechanism by which this occurs is controversial. To elucidate the biochemical mechanism of vitamin E activity, we systematically investigated the effects of its major vitamers and metabolites on lipid oxidation and ferroptosis in a striatal cell model. We found that a specific endogenous metabolite of vitamin E, alpha-tocopherol hydroquinone, was a dramatically more potent inhibitor of ferroptosis than its parent compound, and inhibits 15-lipoxygenase via reduction of the enzyme’s non-heme iron from its active Fe3+ state to an inactive Fe2+ state. Furthermore, a non-metabolizable isosteric analog of vitamin E which retains antioxidant activity neither inhibited 15-lipoxygenase nor prevented ferroptosis. These results call into question the prevailing model that vitamin E acts predominantly as a non-specific lipophilic antioxidant. We propose that, similar to the other lipophilic vitamins A, D and K, vitamin E is instead a pro-vitamin, with its quinone/hydroquinone metabolites responsible for its anti-ferroptotic cytoprotective activity.

Thermodynamic studies revealed that these motions may promote covalent addition of substrate to the enzyme-bound thiamin diphosphate by reducing the free energy of activation. Furthermore, the global dynamics of E1 presumably regulate and streamline the catalytic steps of the overall complex by inducing an entirely entropic (nonmechanical) negative cooperativity with respect to substrate binding at higher temperatures. Our results are consistent with, and reinforce the hypothesis of, coupling of catalysis and regulation with enzyme dynamics and suggest the mechanism by which it is achieved in a key branchpoint enzyme in sugar metabolism.coupling of dynamics to catalysis ͉ EPR ͉ mobile loop dynamics ͉ NMR ͉ pyruvate dehydrogenase T he pyruvate dehydrogenase multienzyme complex (PDHc) is an exquisite machine that catalyzes the oxidative decarboxylation of pyruvate to acetyl CoA (1).In Escherichia coli, the PDHc is composed of multiple copies of three components: E1ec, E2ec, and E3ec, which consecutively catalyze part(s) of the above overall reaction. E1ec is a thiamin diphosphate (ThDP)-dependent ␣ 2 homodimer with mass 198,948 Da and catalyzes the reactions shown in supporting information (SI) Scheme I. The crystal structure of E1ec complexed with ThDP revealed two disordered regions near the active site with no discernible electron density (2), spanning residues 401-413 (inner loop) and 541-557 (outer loop), which become ordered in the presence of C2␣-phosphonolactylThDP (PLThDP), a stable analogue of the first ThDP-bound predecarboxylation covalent intermediate C2␣-lactylThDP (LThDP) (3) (Fig. 1). The enzyme could also catalyze very efficiently the formation of PLThDP from methyl acetylphosphonate (MAP), an excellent electrostatic analogue of pyruvate (SI Scheme II).The dynamic behavior of these active center loops in E1ec is critical for catalytic functions starting from a predecarboxylation event and culminating in transfer of the acetyl moiety to the E2ec component (i.e., intercomponent communication; ref. 4).The disorder-order transformation in E1ec modulated by the interaction of H407 with PLThDP acts as a ''feed-forward'' switch by preparing the active site for the next step, receiving the lipoamide group of the E2ec component (3). These observations suggested that in E1ec, the dynamics of active-center loops may be correlated to substrate turnover. Correlated biological processes of considerable interest, such as ligand binding, catalysis, and conformational transitions, occur on time scales ranging from picoseconds to days, and the conformational transition is often coupled to ligand binding and catalysis (5-7). The relationship between the time scale of such motions and their specific roles in catalysis is an important current issue in enzymology.Author contributions: S.K., G.W.B., W.F., and F.J. designed research; S.K., G.U., and J.S. performed research; S.K., G.U., G.W.B., and F.J. analyzed data; and S.K., G.W.B., and F.J. wrote the paper.The authors declare no conflict of interest.This article is a ...