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Nature Communications Jun 2024Cells depend on their endolysosomal system for nutrient uptake and downregulation of plasma membrane proteins. These processes rely on endosomal maturation, which...
Cells depend on their endolysosomal system for nutrient uptake and downregulation of plasma membrane proteins. These processes rely on endosomal maturation, which requires multiple membrane fusion steps. Early endosome fusion is promoted by the Rab5 GTPase and its effector, the hexameric CORVET tethering complex, which is homologous to the lysosomal HOPS. How these related complexes recognize their specific target membranes remains entirely elusive. Here, we solve the structure of CORVET by cryo-electron microscopy and revealed its minimal requirements for membrane tethering. As expected, the core of CORVET and HOPS resembles each other. However, the function-defining subunits show marked structural differences. Notably, we discover that unlike HOPS, CORVET depends not only on Rab5 but also on phosphatidylinositol-3-phosphate (PI3P) and membrane lipid packing defects for tethering, implying that an organelle-specific membrane code enables fusion. Our data suggest that both shape and membrane interactions of CORVET and HOPS are conserved in metazoans, thus providing a paradigm how tethering complexes function.
Topics: Endosomes; Cryoelectron Microscopy; Phosphatidylinositol Phosphates; Membrane Fusion; rab5 GTP-Binding Proteins; Humans; Vesicular Transport Proteins; Cell Membrane; Animals; Lysosomes
PubMed: 38898033
DOI: 10.1038/s41467-024-49137-9 -
Nature Communications Jun 2024Autophagy is relevant for diverse processes in eukaryotic cells, making its regulation of fundamental importance. The formation and maturation of autophagosomes require...
Autophagy is relevant for diverse processes in eukaryotic cells, making its regulation of fundamental importance. The formation and maturation of autophagosomes require a complex choreography of numerous factors. The endosomal sorting complex required for transport (ESCRT) is implicated in the final step of autophagosomal maturation by sealing of the phagophore membrane. ESCRT-III components were shown to mediate membrane scission by forming filaments that interact with cellular membranes. However, the molecular mechanisms underlying the recruitment of ESCRTs to non-endosomal membranes remain largely unknown. Here we focus on the ESCRT-associated protein ALG2-interacting protein X (ALIX) and identify Ca-dependent lipid binding protein 1 (CaLB1) as its interactor. Our findings demonstrate that CaLB1 interacts with AUTOPHAGY8 (ATG8) and PI(3)P, a phospholipid found in autophagosomal membranes. Moreover, CaLB1 and ALIX localize with ATG8 on autophagosomes upon salt treatment and assemble together into condensates. The depletion of CaLB1 impacts the maturation of salt-induced autophagosomes and leads to reduced delivery of autophagosomes to the vacuole. Here, we propose a crucial role of CaLB1 in augmenting phase separation of ALIX, facilitating the recruitment of ESCRT-III to the site of phagophore closure thereby ensuring efficient maturation of autophagosomes.
Topics: Arabidopsis; Autophagosomes; Endosomal Sorting Complexes Required for Transport; Arabidopsis Proteins; Calcium-Binding Proteins; Autophagy; Phosphatidylinositol Phosphates; Autophagy-Related Protein 8 Family; Vacuoles; Phase Separation
PubMed: 38898014
DOI: 10.1038/s41467-024-49485-6 -
Nature Communications Jun 2024Methaqualone, a quinazolinone marketed commercially as Quaalude, is a central nervous system depressant that was used clinically as a sedative-hypnotic, then became a...
Methaqualone, a quinazolinone marketed commercially as Quaalude, is a central nervous system depressant that was used clinically as a sedative-hypnotic, then became a notorious recreational drug in the 1960s-80s. Due to its high abuse potential, medical use of methaqualone was eventually prohibited, yet it persists as a globally abused substance. Methaqualone principally targets GABA receptors, which are the major inhibitory neurotransmitter-gated ion channels in the brain. The restricted status and limited accessibility of methaqualone have contributed to its pharmacology being understudied. Here, we use cryo-EM to localize the GABA receptor binding sites of methaqualone and its more potent derivative, PPTQ, to the same intersubunit transmembrane sites targeted by the general anesthetics propofol and etomidate. Both methaqualone and PPTQ insert more deeply into subunit interfaces than the previously-characterized modulators. Binding of quinazolinones to this site results in widening of the extracellular half of the ion-conducting pore, following a trend among positive allosteric modulators in destabilizing the hydrophobic activation gate in the pore as a mechanism for receptor potentiation. These insights shed light on the underexplored pharmacology of quinazolinones and further elucidate the molecular mechanisms of allosteric GABA receptor modulation through transmembrane binding sites.
Topics: Receptors, GABA-A; Binding Sites; Cryoelectron Microscopy; Humans; Animals; Etomidate; Propofol; Quinazolinones; Allosteric Regulation; HEK293 Cells; Hypnotics and Sedatives
PubMed: 38898000
DOI: 10.1038/s41467-024-49471-y -
Cell Reports. Medicine Jun 2024ATP-binding cassette (ABC) transporters facilitate the movement of diverse molecules across cellular membranes, including those within the CNS. While most extensively... (Review)
Review
ATP-binding cassette (ABC) transporters facilitate the movement of diverse molecules across cellular membranes, including those within the CNS. While most extensively studied in microvascular endothelial cells forming the blood-brain barrier (BBB), other CNS cell types also express these transporters. Importantly, disruptions in the CNS microenvironment during disease can alter transporter expression and function. Through this comprehensive review, we explore the modulation of ABC transporters in various brain pathologies and the context-dependent consequences of these changes. For instance, downregulation of ABCB1 may exacerbate amyloid beta plaque deposition in Alzheimer's disease and facilitate neurotoxic compound entry in Parkinson's disease. Upregulation may worsen neuroinflammation by aiding chemokine-mediated CD8 T cell influx into multiple sclerosis lesions. Overall, ABC transporters at the BBB hinder drug entry, presenting challenges for effective pharmacotherapy. Understanding the context-dependent changes in ABC transporter expression and function is crucial for elucidating the etiology and developing treatments for brain diseases.
Topics: Humans; ATP-Binding Cassette Transporters; Animals; Blood-Brain Barrier; Brain; Brain Diseases; Alzheimer Disease
PubMed: 38897176
DOI: 10.1016/j.xcrm.2024.101609 -
ELife Jun 2024The protein translocon at the endoplasmic reticulum comprises the Sec61 translocation channel and numerous accessory factors that collectively facilitate the biogenesis...
The protein translocon at the endoplasmic reticulum comprises the Sec61 translocation channel and numerous accessory factors that collectively facilitate the biogenesis of secretory and membrane proteins. Here, we leveraged recent advances in cryo-electron microscopy (cryo-EM) and structure prediction to derive insights into several novel configurations of the ribosome-translocon complex. We show how a transmembrane domain (TMD) in a looped configuration passes through the Sec61 lateral gate during membrane insertion; how a nascent chain can bind and constrain the conformation of ribosomal protein uL22; and how the translocon-associated protein (TRAP) complex can adjust its position during different stages of protein biogenesis. Most unexpectedly, we find that a large proportion of translocon complexes contains RAMP4 intercalated into Sec61's lateral gate, widening Sec61's central pore and contributing to its hydrophilic interior. These structures lead to mechanistic hypotheses for translocon function and highlight a remarkably plastic machinery whose conformations and composition adjust dynamically to its diverse range of substrates.
Topics: Ribosomes; Cryoelectron Microscopy; SEC Translocation Channels; Endoplasmic Reticulum; Protein Conformation; Ribosomal Proteins; Humans; Models, Molecular; Protein Transport; Membrane Proteins
PubMed: 38896445
DOI: 10.7554/eLife.95814 -
ELife Jun 2024The CALHM proteins constitute a family of large pore channels that contains six closely related paralogs in humans. Two family members, CALHM1 and 3, have been...
The CALHM proteins constitute a family of large pore channels that contains six closely related paralogs in humans. Two family members, CALHM1 and 3, have been associated with the release of ATP during taste sensation. Both proteins form heteromeric channels that activate at positive potential and decreased extracellular Ca concentration. Although the structures of several family members displayed large oligomeric organizations of different size, their function has in most cases remained elusive. Our previous study has identified the paralogs CALHM2, 4 and, 6 to be highly expressed in the placenta and defined their structural properties as membrane proteins exhibiting features of large pore channels with unknown activation properties (Drożdżyk et al., 2020). Here, we investigated whether these placental paralogs would form heteromers and characterized heteromeric complexes consisting of CALHM2 and CALHM4 subunits using specific binders as fiducial markers. Both proteins assemble with different stoichiometries with the largest population containing CALHM2 as the predominant component. In these oligomers, the subunits segregate and reside in their preferred conformation found in homomeric channels. Our study has thus revealed the properties that govern the formation of CALHM heteromers in a process of potential relevance in a cellular context.
Topics: Humans; Protein Multimerization; Calcium Channels; HEK293 Cells; Female; Placenta; Protein Conformation
PubMed: 38896440
DOI: 10.7554/eLife.96138 -
Open Biology Jun 2024Acid-sensing ion channels (ASICs) are neuronal Na-permeable ion channels activated by extracellular acidification. ASICs are involved in learning, fear sensing, pain...
Acid-sensing ion channels (ASICs) are neuronal Na-permeable ion channels activated by extracellular acidification. ASICs are involved in learning, fear sensing, pain sensation and neurodegeneration. Increasing the extracellular Ca concentration decreases the H sensitivity of ASIC1a, suggesting a competition for binding sites between H and Ca ions. Here, we predicted candidate residues for Ca binding on ASIC1a, based on available structural information and our molecular dynamics simulations. With functional measurements, we identified several residues in cavities previously associated with pH-dependent gating, whose mutation reduced the modulation by extracellular Ca of the ASIC1a pH dependence of activation and desensitization. This occurred likely owing to a disruption of Ca binding. Our results link one of the two predicted Ca-binding sites in each ASIC1a acidic pocket to the modulation of channel activation. Mg regulates ASICs in a similar way as does Ca. We show that Mg shares some of the binding sites with Ca. Finally, we provide evidence that some of the ASIC1a Ca-binding sites are functionally conserved in the splice variant ASIC1b. Our identification of divalent cation-binding sites in ASIC1a shows how Ca affects ASIC1a gating, elucidating a regulatory mechanism present in many ion channels.
Topics: Acid Sensing Ion Channels; Binding Sites; Calcium; Animals; Molecular Dynamics Simulation; Protein Binding; Hydrogen-Ion Concentration; Magnesium; Humans; Ion Channel Gating; Mutation; Protein Conformation
PubMed: 38896086
DOI: 10.1098/rsob.240028 -
Cancer Medicine Jun 2024ATP-binding cassette subfamily G member 1 is mostly known as a transporter for intracellular cholesterol efflux, and a number of studies indicate that ABCG1 also... (Review)
Review
BACKGROUND
ATP-binding cassette subfamily G member 1 is mostly known as a transporter for intracellular cholesterol efflux, and a number of studies indicate that ABCG1 also functions actively in tumor initiation and progression. This review aimed to provide an overall review of how ABCG1 acts in tumor progression.
METHOD
A comprehensive searching about ABCG1 and tumor was conducted up to November 2023 using proper keywords through databases including PubMed and Web of Science.
RESULT
Overall, ABCG1 plays a crucial role in the development of multiple tumorigenesis. ABCG1 enhances tumor-promoting ability through conferring stem-like properties to cancer cells and mediates chemoresistance in multiple cancers. Additionally, ABCG1 may act as a kinase to phosphorylate downstream molecules and induces tumor growth. In tumor microenvironment, ABCG1 plays a substantial role in immunity response through macrophages to create a tumor-favoring circumstance.
CONCLUSION
High expression of ABCG1 is usually associated with poor prognosis, which means ABCG1 may be a potential biomarker for early diagnosis and prognosis of various cancers. ABCG1-targeted therapy may provide a novel treatment for cancer patients.
Topics: Humans; ATP Binding Cassette Transporter, Subfamily G, Member 1; Neoplasms; Disease Progression; Tumor Microenvironment; Drug Resistance, Neoplasm; Biomarkers, Tumor; Prognosis; Animals; Gene Expression Regulation, Neoplastic
PubMed: 38896016
DOI: 10.1002/cam4.7285 -
Human Brain Mapping Jun 2024Quantitative susceptibility mapping (QSM) is an MRI modality used to non-invasively measure iron content in the brain. Iron exhibits a specific anatomically varying...
Quantitative susceptibility mapping (QSM) is an MRI modality used to non-invasively measure iron content in the brain. Iron exhibits a specific anatomically varying pattern of accumulation in the brain across individuals. The highest regions of accumulation are the deep grey nuclei, where iron is stored in paramagnetic molecule ferritin. This form of iron is considered to be what largely contributes to the signal measured by QSM in the deep grey nuclei. It is also known that QSM is affected by diamagnetic myelin contents. Here, we investigate spatial gene expression of iron and myelin related genes, as measured by the Allen Human Brain Atlas, in relation to QSM images of age-matched subjects. We performed multiple linear regressions between gene expression and the average QSM signal within 34 distinct deep grey nuclei regions. Our results show a positive correlation (p < .05, corrected) between expression of ferritin and the QSM signal in deep grey nuclei regions. We repeated the analysis for other genes that encode proteins thought to be involved in the transport and storage of iron in the brain, as well as myelination. In addition to ferritin, our findings demonstrate a positive correlation (p < .05, corrected) between the expression of ferroportin, transferrin, divalent metal transporter 1, several gene markers of myelinating oligodendrocytes, and the QSM signal in deep grey nuclei regions. Our results suggest that the QSM signal reflects both the storage and active transport of iron in the deep grey nuclei regions of the brain.
Topics: Humans; Iron; Magnetic Resonance Imaging; Male; Female; Myelin Sheath; Adult; Homeostasis; Ferritins; Brain; Gene Expression; Middle Aged; Cation Transport Proteins; Young Adult; Brain Mapping
PubMed: 38896001
DOI: 10.1002/hbm.26688 -
BioRxiv : the Preprint Server For... Jun 2024Based on genetic studies, lysosome dysfunction is thought to play a pathogenetic role in Parkinson's disease (PD). Here we show that VPS13C, a bridge-like lipid...
Based on genetic studies, lysosome dysfunction is thought to play a pathogenetic role in Parkinson's disease (PD). Here we show that VPS13C, a bridge-like lipid transport protein and a PD gene, is a sensor of lysosome stress/damage. Upon lysosome membrane perturbation, VPS13C rapidly relocates from the cytosol to the surface of lysosomes where it tethers their membranes to the ER. This recruitment depends on Rab7 and requires release of a brake, most likely an intramolecular interaction within VPS13C, which hinders access of its VAB domain to lysosome-bound Rab7. While another PD protein, LRRK2, is also recruited to stressed/damaged lysosomes, its recruitment occurs at much later stages and by different mechanisms. Given the putative role of VPS13 proteins in bulk lipid transport, these findings suggest lipid delivery to lysosomes by VPS13C is part of an early response to lysosome damage.
PubMed: 38895395
DOI: 10.1101/2024.06.08.598070