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Nature Jul 2023Voltage-gated ion channels (VGICs) comprise multiple structural units, the assembly of which is required for function. Structural understanding of how VGIC subunits...
Voltage-gated ion channels (VGICs) comprise multiple structural units, the assembly of which is required for function. Structural understanding of how VGIC subunits assemble and whether chaperone proteins are required is lacking. High-voltage-activated calcium channels (Cas) are paradigmatic multisubunit VGICs whose function and trafficking are powerfully shaped by interactions between pore-forming Ca1 or Ca2 Caα (ref. ), and the auxiliary Caβ and Caαδ subunits. Here we present cryo-electron microscopy structures of human brain and cardiac Ca1.2 bound with Caβ to a chaperone-the endoplasmic reticulum membrane protein complex (EMC)-and of the assembled Ca1.2-Caβ-Caαδ-1 channel. These structures provide a view of an EMC-client complex and define EMC sites-the transmembrane (TM) and cytoplasmic (Cyto) docks; interaction between these sites and the client channel causes partial extraction of a pore subunit and splays open the Caαδ-interaction site. The structures identify the Caαδ-binding site for gabapentinoid anti-pain and anti-anxiety drugs, show that EMC and Caαδ interactions with the channel are mutually exclusive, and indicate that EMC-to-Caαδ hand-off involves a divalent ion-dependent step and Ca1.2 element ordering. Disruption of the EMC-Ca complex compromises Ca function, suggesting that the EMC functions as a channel holdase that facilitates channel assembly. Together, the structures reveal a Ca assembly intermediate and EMC client-binding sites that could have wide-ranging implications for the biogenesis of VGICs and other membrane proteins.
Topics: Humans; Binding Sites; Brain; Calcium Channels, L-Type; Cryoelectron Microscopy; Endoplasmic Reticulum; Gabapentin; Membrane Proteins; Myocardium
PubMed: 37196677
DOI: 10.1038/s41586-023-06175-5 -
International Journal of Molecular... May 2022Protein import into the endoplasmic reticulum (ER) is the first step in the biogenesis of approximately 10,000 different soluble and membrane proteins of human cells,...
Protein import into the endoplasmic reticulum (ER) is the first step in the biogenesis of approximately 10,000 different soluble and membrane proteins of human cells, which amounts to about 30% of the proteome [...].
Topics: Endoplasmic Reticulum; Humans; Membrane Proteins; Protein Transport
PubMed: 35628123
DOI: 10.3390/ijms23105315 -
American Journal of Physiology. Cell... Jan 2020The anterior gradient-2 (AGR2) is an endoplasmic reticulum (ER)-resident protein belonging to the protein disulfide isomerase family that mediates the formation of... (Review)
Review
The anterior gradient-2 (AGR2) is an endoplasmic reticulum (ER)-resident protein belonging to the protein disulfide isomerase family that mediates the formation of disulfide bonds and assists the protein quality control in the ER. In addition to its role in proteostasis, extracellular AGR2 is responsible for various cellular effects in many types of cancer, including cell proliferation, survival, and metastasis. Various OMICs approaches have been used to identify AGR2 binding partners and to investigate the functions of AGR2 in the ER and outside the cell. Emerging data showed that AGR2 exists not only as monomer, but it can also form homodimeric structure and thus interact with different partners, yielding different biological outcomes. In this review, we summarize the AGR2 "interactome" and discuss the pathological and physiological role of such AGR2 interactions.
Topics: Animals; Endoplasmic Reticulum; Humans; Mucoproteins; Multiprotein Complexes; Oncogene Proteins; Protein Binding; Protein Interaction Domains and Motifs; Signal Transduction
PubMed: 31644305
DOI: 10.1152/ajpcell.00532.2018 -
Virology May 2015Poxviruses differ from most DNA viruses by replicating entirely within the cytoplasm. The first discernible viral structures are crescents and spherical immature virions... (Review)
Review
Poxviruses differ from most DNA viruses by replicating entirely within the cytoplasm. The first discernible viral structures are crescents and spherical immature virions containing a single lipoprotein membrane bilayer with an external honeycomb lattice. Because this viral membrane displays no obvious continuity with a cellular organelle, a de novo origin was suggested. Nevertheless, transient connections between viral and cellular membranes could be difficult to resolve. Despite the absence of direct evidence, the intermediate compartment (ERGIC) between the endoplasmic reticulum (ER) and Golgi apparatus and the ER itself were considered possible sources of crescent membranes. A break-through in understanding poxvirus membrane biogenesis has come from recent studies of the abortive replication of several vaccinia virus null mutants. Novel images showing continuity between viral crescents and the ER and the accumulation of immature virions in the expanded ER lumen provide the first direct evidence for a cellular origin of this poxvirus membrane.
Topics: Animals; Endoplasmic Reticulum; Host-Pathogen Interactions; Humans; Intracellular Membranes; Poxviridae; Virus Assembly
PubMed: 25728299
DOI: 10.1016/j.virol.2015.02.003 -
ELife May 2024Advanced cryo-EM approaches reveal surprising insights into the molecular structure that allows nascent proteins to be inserted into the membrane of the endoplasmic...
Advanced cryo-EM approaches reveal surprising insights into the molecular structure that allows nascent proteins to be inserted into the membrane of the endoplasmic reticulum.
Topics: Endoplasmic Reticulum; Cryoelectron Microscopy; Protein Transport; Membrane Proteins
PubMed: 38787756
DOI: 10.7554/eLife.98548 -
Molecular Cell Aug 2022Protein import into mitochondria is a highly regulated process, yet how cells clear mitochondria undergoing dysfunctional protein import remains poorly characterized....
Protein import into mitochondria is a highly regulated process, yet how cells clear mitochondria undergoing dysfunctional protein import remains poorly characterized. Here we showed that mitochondrial protein import stress (MPIS) triggers localized LC3 lipidation. This arm of the mitophagy pathway occurs through the Nod-like receptor (NLR) protein NLRX1 while, surprisingly, without the engagement of the canonical mitophagy protein PINK1. Mitochondrial depolarization, which itself induces MPIS, also required NLRX1 for LC3 lipidation. While normally targeted to the mitochondrial matrix, cytosol-retained NLRX1 recruited RRBP1, a ribosome-binding transmembrane protein of the endoplasmic reticulum, which relocated to the mitochondrial vicinity during MPIS, and the NLRX1/RRBP1 complex in turn controlled the recruitment and lipidation of LC3. Furthermore, NLRX1 controlled skeletal muscle mitophagy in vivo and regulated endurance capacity during exercise. Thus, localization and lipidation of LC3 at the site of mitophagosome formation is a regulated step of mitophagy controlled by NLRX1/RRBP1 in response to MPIS.
Topics: Endoplasmic Reticulum; Mitochondria; Mitochondrial Proteins; Mitophagy; Protein Transport
PubMed: 35752171
DOI: 10.1016/j.molcel.2022.06.004 -
Cell Death and Differentiation Mar 2020Autophagy regulates the degradation of unnecessary or dysfunctional cellular components. This catabolic process requires the formation of a double-membrane vesicle, the... (Review)
Review
Autophagy regulates the degradation of unnecessary or dysfunctional cellular components. This catabolic process requires the formation of a double-membrane vesicle, the autophagosome, that engulfs the cytosolic material and delivers it to the lysosome. Substrate specificity is achieved by autophagy receptors, which are characterized by the presence of at least one LC3-interaction region (LIR) or GABARAP-interaction motif (GIM). Only recently, several receptors that mediate the specific degradation of endoplasmic reticulum (ER) components via autophagy have been identified (the process known as ER-phagy or reticulophagy). Here, we give an update on the current knowledge about the role of ER-phagy receptors in health and disease.
Topics: Animals; Autophagy; Disease; Endoplasmic Reticulum; Homeostasis; Humans
PubMed: 31659280
DOI: 10.1038/s41418-019-0444-0 -
Current Opinion in Structural Biology Jun 2023Cells store lipids as a reservoir of metabolic energy and membrane component precursors in organelles called lipid droplets (LDs). LD formation occurs in the endoplasmic... (Review)
Review
Cells store lipids as a reservoir of metabolic energy and membrane component precursors in organelles called lipid droplets (LDs). LD formation occurs in the endoplasmic reticulum (ER) at LD assembly complexes (LDAC), consisting of an oligomeric core of seipin and accessory proteins. LDACs determine the sites of LD formation and are required for this process to occur normally. Seipin oligomers form a cage-like structure in the membrane that may serve to facilitate the phase transition of neutral lipids in the membrane to form an oil droplet within the LDAC. Modeling suggests that, as the LD grows, seipin anchors it to the ER bilayer and conformational shifts of seipin transmembrane segments open the LDAC dome toward the cytoplasm, enabling the emerging LD to egress from the ER.
Topics: Lipid Droplets; Proteins; Endoplasmic Reticulum; Lipids; Lipid Metabolism
PubMed: 37150040
DOI: 10.1016/j.sbi.2023.102606 -
Annual Review of Nutrition Jul 2016The endoplasmic reticulum is the port of entry for proteins into the secretory pathway and the site of synthesis for several important lipids, including cholesterol,... (Review)
Review
The endoplasmic reticulum is the port of entry for proteins into the secretory pathway and the site of synthesis for several important lipids, including cholesterol, triacylglycerol, and phospholipids. Protein production within the endoplasmic reticulum is tightly regulated by a cohort of resident machinery that coordinates the folding, modification, and deployment of secreted and integral membrane proteins. Proteins failing to attain their native conformation are degraded through the endoplasmic reticulum-associated degradation (ERAD) pathway via a series of tightly coupled steps: substrate recognition, dislocation, and ubiquitin-dependent proteasomal destruction. The same ERAD machinery also controls the flux through various metabolic pathways by coupling the turnover of metabolic enzymes to the levels of key metabolites. We review the current understanding and biological significance of ERAD-mediated regulation of lipid metabolism in mammalian cells.
Topics: Animals; Cholesterol; Endoplasmic Reticulum; Endoplasmic Reticulum-Associated Degradation; Gene Expression Regulation, Enzymologic; Homeostasis; Humans; Lipid Metabolism; Lipoproteins; Models, Biological; Protein Biosynthesis; Protein Folding; Protein Stability; Secretory Pathway; Triglycerides
PubMed: 27296502
DOI: 10.1146/annurev-nutr-071715-051030 -
Advances in Cancer Research 2017Cancer survival is largely impacted by the dissemination of cancer cells from the original tumor site to secondary tissues or organs through metastasis. Targets for... (Review)
Review
Cancer survival is largely impacted by the dissemination of cancer cells from the original tumor site to secondary tissues or organs through metastasis. Targets for antimetastatic therapies have recently become a focus of research, but progress will require a better understanding of the molecular mechanisms driving metastasis. Selenoproteins play important roles in many of the cellular activities underlying metastasis including cell adhesion, matrix degradation and migration, invasion into the blood and extravasation into secondary tissues, and subsequent proliferation into metastatic tumors along with the angiogenesis required for growth. In this review the roles identified for different selenoproteins in these steps and how they may promote or inhibit metastatic cancers is discussed. These roles include selenoenzyme modulation of redox tone and detoxification of reactive oxygen species, calcium homeostasis and unfolded protein responses regulated by endoplasmic reticulum selenoproteins, and the multiple physiological responses influenced by other selenoproteins.
Topics: Animals; Endoplasmic Reticulum; Humans; Neoplasm Metastasis; Neoplasms; Neovascularization, Pathologic; Oxidation-Reduction; Reactive Oxygen Species; Selenoproteins
PubMed: 29054423
DOI: 10.1016/bs.acr.2017.07.008