The essential bacterial protein FtsZ is a GTPase that self-assembles into a structure at the division site termed the “Z-ring”. During cytokinesis, the Z-ring exerts a constrictive force on the membrane by utilizing the chemical energy of GTP hydrolysis. However, the structural basis of this constriction remains unresolved. Here, we present the crystal structure of a GDP-bound Mycobacterium tuberculosis FtsZ (MtbFtsZ) protofilament, which exhibits a curved conformational state. The structure reveals a longitudinal interface that is important for function. The protofilament curvature highlights a hydrolysis-dependent conformational switch at the T3 loop that leads to longitudinal bending between subunits, which could generate sufficient force to drive cytokinesis.

Chronic inflammation is the primary cause of gastric cancer (GC). NLRP3, as an important inflammasome component, has crucial roles in initiating inflammation. However, the potential roles of NLRP3 in GC is unknown. Here, we show that NLRP3 expression is markedly upregulated in GC, which promotes NLRP3 inflammasome activation and interleukin-1β (IL-1β) secretion in macrophages. In addition, NLRP3 binds to cyclin-D1 (CCND1) promoter and promotes its transcription in gastric epithelial cells. Consequently, NLRP3 enhances epithelial cells proliferation and GC tumorigenesis. Furthermore, we identify miR-22, which is constitutively expressed in gastric mucosa, as a suppressor of NLRP3. MiR-22 directly targets NLRP3 and attenuates its oncogenic effects in vitro and in vivo. However, Helicobacter pylori (H. pylori) infection suppresses miR-22 expression, while enhances NLRP3 expression, and that triggers uncontrolled proliferation of epithelial cells and the emergence of GC. Thus, our research describes a mechanism by which miR-22 suppresses NLRP3 and maintains homeostasis of gastric microenvironments and suggests miR-22 as a potential target for the intervention of GC.

Mitochondria undergo frequent morphological changes through fission and fusion. Mutations in core members of the mitochondrial fission/fusion machinery are responsible for severe neurodegenerative diseases. However, the mitochondrial fission/fusion mechanisms are poorly understood. We found that the loss of a mitochondrial protein encoding gene, mitoguardin (miga), leads to mitochondrial defects and neurodegeneration in fly eyes. Mammals express two orthologs of miga: Miga1 and Miga2. Both MIGA1 and MIGA2 form homotypic and heterotypic complexes on the outer membrane of the mitochondria. Loss of MIGA results in fragmented mitochondria, whereas overexpression of MIGA leads to clustering and fusion of mitochondria in both fly and mammalian cells. MIGA proteins function downstream of mitofusin and interact with MitoPLD to stabilize MitoPLD and facilitate MitoPLD dimer formation. Therefore, we propose that MIGA proteins promote mitochondrial fusion by regulating mitochondrial phospholipid metabolism via MitoPLD.

Mitochondria-ER contact sites (MERCs) enable communication between the ER and mitochondria and serve as platforms for many cellular events, including autophagy. Nonetheless, the molecular organization of MERCs is not known, and there is no bona fide marker of these contact sites in mammalian cells. In this study, we designed a genetically encoded reporter using split GFP protein for labeling MERCs. We subsequently analyzed its distribution and dynamics during the cell cycle and under stressful cellular conditions such as starvation, apoptosis and ER stress. We found that MERCs are dynamic structures that undergo remodeling within minutes. Mitochondrial morphology, but not ER morphology, affected the distribution of MERCs. We also found that carbonyl cyanidem-chlorophenyl hydrazone (CCCP) and oligomycin A treatment enhanced MERC formation. The stimulations that led to apoptosis or autophagy increased the MERC signal. By contrast, increasing cellular lipid droplet load did not change the pattern of MERCs.

Autophagy helps deliver sequestered intracellular cargo to lysosomes for proteolytic degradation and thereby maintains cellular homeostasis by preventing accumulation of toxic substances in cells. In a forward mosaic screen in Drosophila designed to identify genes required for neuronal function and maintenance, we identified multiple cacophony (cac) mutant alleles. They exhibit an age-dependent accumulation of autophagic vacuoles (AVs) in photoreceptor terminals and eventually a degeneration of the terminals and surrounding glia. cac encodes an α1 subunit of a Drosophila voltage-gated calcium channel (VGCC) that is required for synaptic vesicle fusion with the plasma membrane and neurotransmitter release. Here, we show that cac mutant photoreceptor terminals accumulate AV-lysosomal fusion intermediates, suggesting that Cac is necessary for the fusion of AVs with lysosomes, a poorly defined process. Loss of another subunit of the VGCC, α2δ or straightjacket (stj), causes phenotypes very similar to those caused by the loss of cac, indicating that the VGCC is required for AV-lysosomal fusion. The role of VGCC in AV-lysosomal fusion is evolutionarily conserved, as the loss of the mouse homologues, Cacna1a and Cacna2d2, also leads to autophagic defects in mice. Moreover, we find that CACNA1A is localized to the lysosomes and that loss of lysosomal Cacna1a in cerebellar cultured neurons leads to a failure of lysosomes to fuse with endosomes and autophagosomes. Finally, we show that the lysosomal CACNA1A but not the plasma-membrane resident CACNA1A is required for lysosomal fusion. In summary, we present a model in which the VGCC plays a role in autophagy by regulating the fusion of AVs with lysosomes through its calcium channel activity and hence functions in maintaining neuronal homeostasis.