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ELife Sep 2022Lysosomes are essential for cellular recycling, nutrient signaling, autophagy, and pathogenic bacteria and viruses invasion. Lysosomal fusion is fundamental to cell...
Lysosomes are essential for cellular recycling, nutrient signaling, autophagy, and pathogenic bacteria and viruses invasion. Lysosomal fusion is fundamental to cell survival and requires HOPS, a conserved heterohexameric tethering complex. On the membranes to be fused, HOPS binds small membrane-associated GTPases and assembles SNAREs for fusion, but how the complex fulfills its function remained speculative. Here, we used cryo-electron microscopy to reveal the structure of HOPS. Unlike previously reported, significant flexibility of HOPS is confined to its extremities, where GTPase binding occurs. The SNARE-binding module is firmly attached to the core, therefore, ideally positioned between the membranes to catalyze fusion. Our data suggest a model for how HOPS fulfills its dual functionality of tethering and fusion and indicate why it is an essential part of the membrane fusion machinery.
Topics: Membrane Fusion; Saccharomyces cerevisiae Proteins; Saccharomyces cerevisiae; Cryoelectron Microscopy; rab GTP-Binding Proteins; SNARE Proteins; Lysosomes; Vacuoles
PubMed: 36098503
DOI: 10.7554/eLife.80901 -
International Journal of Molecular... Jun 2022In all eukaryotes, autophagy is the main pathway for nutrient recycling, which encapsulates parts of the cytoplasm and organelles in double-membrane vesicles, and then... (Review)
Review
In all eukaryotes, autophagy is the main pathway for nutrient recycling, which encapsulates parts of the cytoplasm and organelles in double-membrane vesicles, and then fuses with lysosomes/vacuoles to degrade them. Autophagy is a highly dynamic and relatively complex process influenced by multiple factors. Under normal growth conditions, it is maintained at basal levels. However, when plants are subjected to biotic and abiotic stresses, such as pathogens, drought, waterlogging, nutrient deficiencies, etc., autophagy is activated to help cells to survive under stress conditions. At present, the regulation of autophagy is mainly reflected in hormones, second messengers, post-transcriptional regulation, and protein post-translational modification. In recent years, the degradation mechanism of autophagy-related proteins has attracted much attention. In this review, we have summarized how autophagy-related proteins are degraded in yeast, animals, and plants, which will help us to have a more comprehensive and systematic understanding of the regulation mechanisms of autophagy. Moreover, research progress on the degradation of autophagy-related proteins in plants has been discussed.
Topics: Animals; Autophagy; Autophagy-Related Proteins; Lysosomes; Plants; Saccharomyces cerevisiae; Vacuoles
PubMed: 35806307
DOI: 10.3390/ijms23137301 -
The Plant Cell Dec 2019Interactions between plant cells and the environment rely on modulation of protein receptors, transporters, channels, and lipids at the plasma membrane (PM) to... (Review)
Review
Interactions between plant cells and the environment rely on modulation of protein receptors, transporters, channels, and lipids at the plasma membrane (PM) to facilitate intercellular communication, nutrient uptake, environmental sensing, and directional growth. These functions are fine-tuned by cellular pathways maintaining or reducing particular proteins at the PM. Proteins are endocytosed, and their fate is decided between recycling and degradation to modulate localization, abundance, and activity. Selective autophagy is another pathway regulating PM protein accumulation in response to specific conditions or developmental signals. The mechanisms regulating recycling, degradation, and autophagy have been studied extensively, yet we are just now addressing their regulation and coordination. Here, we (1) provide context concerning regulation of protein accumulation, recycling, or degradation by overviewing endomembrane trafficking; (2) discuss pathways regulating recycling and degradation in terms of cellular roles and cargoes; (3) review plant selective autophagy and its physiological significance; (4) focus on two decision-making mechanisms: regulation of recycling versus degradation of PM proteins and coordination between autophagy and vacuolar degradation; and (5) identify future challenges.
Topics: Autophagy; Cell Membrane; Endocytosis; Endosomes; Exocytosis; Membrane Proteins; Plant Proteins; Protein Transport; Proteolysis; Vacuoles
PubMed: 31628169
DOI: 10.1105/tpc.19.00433 -
Frontiers in Cellular and Infection... 2020Lysosomes are an integral part of the intracellular defense system against microbes. Lysosomal homeostasis in the host is adaptable and responds to conditions such as... (Review)
Review
Lysosomes are an integral part of the intracellular defense system against microbes. Lysosomal homeostasis in the host is adaptable and responds to conditions such as infection or nutritional deprivation. Pathogens such as () and avoid lysosomal targeting by actively manipulating the host vesicular trafficking and reside in a vacuole altered from the default lysosomal trafficking. In this review, the mechanisms by which the respective pathogen containing vacuoles (PCVs) intersect with lysosomal trafficking pathways and maintain their distinctness are discussed. Despite such active inhibition of lysosomal targeting, emerging literature shows that different pathogens or pathogen derived products exhibit a global influence on the host lysosomal system. Pathogen mediated lysosomal enrichment promotes the trafficking of a sub-set of pathogens to lysosomes, indicating heterogeneity in the host-pathogen encounter. This review integrates recent advancements on the global lysosomal alterations upon infections and the host protective role of the lysosomes against these pathogens. The review also briefly discusses the heterogeneity in the lysosomal targeting of these pathogens and the possible mechanisms and consequences.
Topics: Host-Pathogen Interactions; Lysosomes; Mycobacterium tuberculosis; Vacuoles
PubMed: 33330138
DOI: 10.3389/fcimb.2020.595502 -
Proceedings of the National Academy of... Jul 2019R-SNAREs (soluble -ethylmaleimide-sensitive factor receptor), Q-SNAREs, and Sec1/Munc18 (SM)-family proteins are essential for membrane fusion in exocytic and endocytic...
R-SNAREs (soluble -ethylmaleimide-sensitive factor receptor), Q-SNAREs, and Sec1/Munc18 (SM)-family proteins are essential for membrane fusion in exocytic and endocytic trafficking. The yeast vacuolar tethering/SM complex HOPS (homotypic fusion and vacuole protein sorting) increases the fusion of membranes bearing R-SNARE to those with 3Q-SNAREs far more than it enhances their -SNARE pairings. We now report that the fusion of these proteoliposomes is also supported by GST-PX or GST-FYVE, recombinant dimeric proteins which tether by binding the phosphoinositides in both membranes. GST-PX is purely a tether, as it supports fusion without SNARE recognition. GST-PX tethering supports the assembly of new, active SNARE complexes rather than enhancing the function of the fusion-inactive SNARE complexes which had spontaneously formed in the absence of a tether. When SNAREs are more disassembled, as by Sec17, Sec18, and ATP (adenosine triphosphate), HOPS is required, and GST-PX does not suffice. We propose a working model where tethering orients SNARE domains for parallel, active assembly.
Topics: Adenosine Triphosphatases; Adenosine Triphosphate; Endocytosis; Exocytosis; Glutathione Peroxidase; Membrane Fusion; Membrane Fusion Proteins; Phosphatidylinositols; Protein Multimerization; Protein Transport; R-SNARE Proteins; Recombinant Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; Vacuoles; Vesicular Transport Proteins
PubMed: 31235584
DOI: 10.1073/pnas.1907640116 -
The New Phytologist Apr 2020Vacuolar processing enzyme (VPE) is a cysteine-type endopeptidase that has a substrate-specificity for asparagine or aspartic acid residues and cleaves peptide bonds at... (Review)
Review
Vacuolar processing enzyme (VPE) is a cysteine-type endopeptidase that has a substrate-specificity for asparagine or aspartic acid residues and cleaves peptide bonds at their carboxyl-terminal side. Various vacuolar proteins are synthesized as larger proprotein precursors, and VPE is an important initiator of maturation and activation of these proteins. It mediates programmed cell death (PCD) by provoking vacuolar rupture and initiating the proteolytic cascade leading to PCD. Vacuolar processing enzyme also possesses a peptide ligation activity, which is responsible for producing cyclic peptides in several plant species. These unique functions of VPE support developmental and environmental responses in plants. The number of VPE homologues is higher in angiosperm species, indicating that there has been differentiation and specialization of VPE function over the course of evolution. Angiosperm VPEs are separated into two major types: the γ-type VPEs, which are expressed mainly in vegetative organs, and the β-type VPEs, whose expression occurs mainly in storage organs; in eudicots, the δ-type VPEs are further separated within γ-type VPEs. This review also considers the importance of processing and peptide ligation by VPE in vacuolar protein maturation.
Topics: Animals; Cysteine Endopeptidases; Life Cycle Stages; Plant Proteins; Plants; Vacuoles
PubMed: 31679161
DOI: 10.1111/nph.16306 -
The Journal of Cell Biology Oct 2019Protein folding is inherently error prone, especially in the endoplasmic reticulum (ER). Even with an elaborate network of molecular chaperones and protein folding... (Review)
Review
Protein folding is inherently error prone, especially in the endoplasmic reticulum (ER). Even with an elaborate network of molecular chaperones and protein folding facilitators, misfolding can occur quite frequently. To maintain protein homeostasis, eukaryotes have evolved a series of protein quality-control checkpoints. When secretory pathway quality-control pathways fail, stress response pathways, such as the unfolded protein response (UPR), are induced. In addition, the ER, which is the initial hub of protein biogenesis in the secretory pathway, triages misfolded proteins by delivering substrates to the proteasome or to the lysosome/vacuole through ER-associated degradation (ERAD) or ER-phagy. Some misfolded proteins escape the ER and are instead selected for Golgi quality control. These substrates are targeted for degradation after retrieval to the ER or delivery to the lysosome/vacuole. Here, we discuss how these guardian pathways function, how their activities intersect upon induction of the UPR, and how decisions are made to dispose of misfolded proteins in the secretory pathway.
Topics: Animals; Endoplasmic Reticulum; Humans; Lysosomes; Proteins; Secretory Pathway; Vacuoles
PubMed: 31537714
DOI: 10.1083/jcb.201906047 -
PLoS Pathogens Jul 2023L. pneumophila propagates in eukaryotic cells within a specialized niche, the Legionella-containing vacuole (LCV). The infection process is controlled by over 330...
L. pneumophila propagates in eukaryotic cells within a specialized niche, the Legionella-containing vacuole (LCV). The infection process is controlled by over 330 effector proteins delivered through the type IV secretion system. In this study, we report that the Legionella MavH effector localizes to endosomes and remodels host actin cytoskeleton in a phosphatidylinositol 3-phosphate (PI(3)P) dependent manner when ectopically expressed. We show that MavH recruits host actin capping protein (CP) and actin to the endosome via its CP-interacting (CPI) motif and WH2-like actin-binding domain, respectively. In vitro assays revealed that MavH stimulates actin assembly on PI(3)P-containing liposomes causing their tubulation. In addition, the recruitment of CP by MavH negatively regulates F-actin density at the membrane. We further show that, in L. pneumophila-infected cells, MavH appears around the LCV at the very early stage of infection and facilitates bacterium entry into the host. Together, our results reveal a novel mechanism of membrane tubulation induced by membrane-dependent actin polymerization catalyzed by MavH that contributes to the early stage of L. pneumophila infection by regulating host actin dynamics.
Topics: Legionella pneumophila; Actins; Polymerization; Phosphatidylinositol Phosphates; Vacuoles; Bacterial Proteins
PubMed: 37463171
DOI: 10.1371/journal.ppat.1011512 -
Frontiers in Cellular and Infection... 2021malaria remains a global health problem as parasites continue to develop resistance to all antimalarials in use. Infection causes clinical symptoms during the... (Review)
Review
malaria remains a global health problem as parasites continue to develop resistance to all antimalarials in use. Infection causes clinical symptoms during the intra-erythrocytic stage of the lifecycle where the parasite infects and replicates within red blood cells (RBC). During this stage, digests the main constituent of the RBC, hemoglobin, in a specialized acidic compartment termed the digestive vacuole (DV), a process essential for survival. Many therapeutics in use target one or multiple aspects of the DV, with chloroquine and its derivatives, as well as artemisinin, having mechanisms of action within this organelle. In order to better understand how current therapeutics and those under development target DV processes, techniques used to investigate the DV are paramount. This review outlines the involvement of the DV in therapeutics currently in use and focuses on the range of techniques that are currently utilized to study this organelle including microscopy, biochemical analysis, genetic approaches and metabolomic studies. Importantly, continued development and application of these techniques will aid in our understanding of the DV and in the development of new therapeutics or therapeutic partners for the future.
Topics: Antimalarials; Chloroquine; Humans; Malaria, Falciparum; Plasmodium falciparum; Vacuoles
PubMed: 35096663
DOI: 10.3389/fcimb.2021.829823 -
The New Phytologist Feb 2020Active removal of Na from the cytosol into the vacuole plays a critical role in salinity tissue tolerance, but another, often neglected component of this trait is Na... (Review)
Review
Active removal of Na from the cytosol into the vacuole plays a critical role in salinity tissue tolerance, but another, often neglected component of this trait is Na retention in vacuoles. This retention is based on an efficient control of Na -permeable slow- and fast-vacuolar channels that mediate the back-leak of Na into cytosol and, if not regulated tightly, could result in a futile cycle. This Tansley insight summarizes our current knowledge of regulation of tonoplast Na -permeable channels and discusses the energy cost of vacuolar Na sequestration, under different scenarios. We also report on a phylogenetic and bioinformatic analysis of the plant two-pore channel family and the difference in its structure and regulation between halophytes and glycophytes, in the context of salinity tolerance.
Topics: Energy Metabolism; Plant Proteins; Proton Pumps; Salt-Tolerant Plants; Sodium; Vacuoles
PubMed: 30802968
DOI: 10.1111/nph.15758