Recent findings have revealed that the protein gasdermin D (GSDMD) plays key roles in cell pyroptosis. GSDMD binds lipids and forms pore structures to induce pyroptosis upon microbial infection and associated danger signals. However, detailed structural information for GSDMD remains unknown. Here, we report the crystal structure of the C-terminal domain of human GSDMD (GSDMD-C) at 2.64-Å resolution. The first loop on GSDMD-C inserts into the N-terminal domain (GSDMD-N), which helps stabilize the conformation of the full-length GSDMD. Substitution of this region by a short linker sequence increased levels of cell death. Mutants F283A and F283R can increase protein heterogeneity in vitro and are capable of undergoing cell pyroptosis in 293T cells. The small-angle X-ray–scattering envelope of human GSDMD is consistent with the modeled GSDMD structure and mouse GSDMA3 structure, which suggests that GSDMD adopts an autoinhibited conformation in solution. The positive potential surface of GSDMD-N covered by GSDMD-C is exposed after being released from the autoinhibition state and can form high-order oligomers via a charge–charge interaction. Furthermore, by mapping different regions of GSDMD, we determined that one short segment is sufficient to kill bacteria in vitro and can efficiently inhibit cell growth in Escherichia coli and Mycobacterium Smegmatis. These findings reveal that GSDMD-C acts as an auto-inhibition executor and GSDMD-N could form pore structures via a charge–charge interaction upon cleavage by caspases during cell pyroptosis.

The conversion of serine and glycine that is accomplished by serine hydroxymethyltransferase 2 (SHMT2) in mitochondria is significantly upregulated in various cancers to support cancer cell proliferation. In this study, we observed that SHMT2 is acetylated at K95 in colorectal cancer (CRC) cells. SIRT3, the major deacetylase in mitochondria, is responsible for SHMT2 deacetylation. SHMT2-K95-Ac disrupts its functional tetramer structure and inhibits its enzymatic activity. SHMT2-K95-Ac also promotes its degradation via the K63-ubiquitin–lysosome pathway in a glucose-dependent manner. TRIM21 acts as an E3 ubiquitin ligase for SHMT2. SHMT2-K95-Ac decreases CRC cell proliferation and tumor growth in vivo through attenuation of serine consumption and reduction in NADPH levels. Finally, SHMT2-K95-Ac is significantly decreased in human CRC samples and is inversely associated with increased SIRT3 expression, which is correlated with poorer postoperative overall survival. Our study reveals the unknown mechanism of SHMT2 regulation by acetylation which is involved in colorectal carcinogenesis.

Innate immune responses depend on timely recognition of pathogenic or danger signals by multiple cell surface or cytoplasmic receptors and transmission of signals for proper counteractions through adaptor and effector molecules. At the forefront of innate immunity are four major signaling pathways, including those elicited by Toll-like receptors, RIG-I-like receptors, inflammasomes, or cGAS, each with its own cellular localization, ligand specificity, and signal relay mechanism. They collectively engage a number of overlapping signaling outcomes, such as NF-κB activation, interferon response, cytokine maturation, and cell death. Several proteins often assemble into a supramolecular complex to enable signal transduction and amplification. In this article, we review the recent progress in mechanistic delineation of proteins in these pathways, their structural features, modes of ligand recognition, conformational changes, and homo- and hetero-oligomeric interactions within the supramolecular complexes. Regardless of seemingly distinct interactions and mechanisms, the recurring themes appear to consist of autoinhibited resting-state receptors, ligand-induced conformational changes, and higher-order assemblies of activated receptors, adaptors, and signaling enzymes through conserved protein-protein interactions.