Pyroptosis is a type of programmed necrosis triggered by the detection of pathogens or endogenous danger signals in the cytosol. Pyroptotic cells exhibit a swollen, enlarged morphology and ultimately Show more
Pyroptosis is a type of programmed necrosis triggered by the detection of pathogens or endogenous danger signals in the cytosol. Pyroptotic cells exhibit a swollen, enlarged morphology and ultimately undergo lysis, releasing their cytosolic contents - such as proteins, metabolites, and nucleic acids - into the extracellular space. These molecules can function as danger-associated molecular patterns (DAMPs), triggering inflammation when detected by neighboring cells. Mechanistically, pyroptosis is initiated by members of the gasdermin protein family, which were identified a decade ago as pore-forming executors of cell death. Mammalian gasdermins consist of a cytotoxic N-terminal domain, a flexible linker, and a C-terminal regulatory domain that binds to and inhibits the N-terminus. Proteolytic cleavage within the linker releases the N-terminal domain, enabling it to target various cellular membranes, including nuclear, mitochondrial, and plasma membranes, where it forms large transmembrane pores. Gasdermin pores in the plasma membrane disrupt the electrochemical gradient, leading to water influx and cell swelling. Their formation also activates the membrane protein ninjurin-1 (NINJ1), which oligomerizes to drive complete plasma membrane rupture and the release of large DAMPs. Since their discovery as pore-forming proteins, gasdermins have been linked to pyroptosis not only in host defense but also in various pathological conditions. This review explores the history of pyroptosis, recent insights into gasdermin activation, the cellular consequences of pore formation, and the physiological roles of pyroptosis. Show less
Cytochrome c binds to cardiolipin (CL) on the inner mitochondrial membrane during the initial stages of apoptosis where it oxidizes CL, promoting its release into the cytoplasm where it initiates apop Show more
Cytochrome c binds to cardiolipin (CL) on the inner mitochondrial membrane during the initial stages of apoptosis where it oxidizes CL, promoting its release into the cytoplasm where it initiates apoptosis. Previous work has identified interaction sites on cytochrome c involved in the cytochrome c-CL interaction. The contributions of the lysines attributed to site A, the anionic site, are studied here to elucidate the relative importance of each for electrostatic interaction of cytochrome c with CL at pH 8, conditions where site A is dominant. A set of single, double, and quadruple lysine to alanine variants of yeast iso-1-cytochrome c, at sequence positions 72, 73, 86, and 87, show that all contribute to the site A-mediated interaction with CL. All variants experience two sequential structural rearrangements as the lipid to protein ratio (LPR) increases. At a low LPR near 10, all variants undergo a small heme-centered structural change detected by Soret circular dichroism. At higher LPRs ranging from 22 to 34, all variants partially unfold as detected by Trp59 emission. The robustness of the mechanism of interaction to sequential neutralization of the four lysines assigned to site A demonstrates that site A is more extensive than previously supposed. The nature of both structural rearrangements also depends on which lysines constitute site A. The peroxidase activity of cytochrome c in the early stages of apoptosis depends on the nature of structural rearrangement near the heme. Thus, the lysines that comprise site A may have evolved to optimize the peroxidase signaling switch. Show less