Cryo-EM structures of SERCA2b reveal the mechanism of regulation by the luminal extension tail

Sarcoendoplasmic reticulum calcium ATPase is an essential and druggable lipid-dependent ion pump in Toxoplasma gondii

Toxoplasma gondii is a common intracellular pathogenic protist causing acute and chronic infections in many warm-blooded organisms. Calcium homeostasis is pivotal for its asexual reproduction in mammalian host cells, and sarcoendoplasmic reticulum calcium-ATPase (SERCA) is considered vital for maintaining ion homeostasis within the parasite. This work studied the physiological relevance, structure-function relationship, mechanism, and therapeutic value of SERCA in the acutely-infectious tachyzoite stage of T. gondii. A conditional depletion of SERCA, located in the endoplasmic reticulum, by auxin-inducible degradation is lethal for the parasite due to severe defects in its replication, gliding motility, and invasion. The observed phenotypes are caused by dysregulated calcium ion homeostasis and microneme secretion in the absence of TgSERCA. Furthermore, ectopic expression of TgSERCA restored the lytic cycle of a phosphatidylthreonine-null and phosphatidylserine-enriched mutant with perturbed calcium homeostasis, motility and invasion. These lipids are expressed in the parasite ER, co-localizing with TgSERCA. Last but not least, the structure-function modeling and ligand docking of TgSERCA with a library comprising >5000 chemicals identified two compounds (RB-15, NR-301) that inhibited the lytic cycle by affecting the tachyzoite locomotion, invasion, microneme discharge, and calcium levels. In conclusion, we demonstrate TgSERCA as an indispensable lipid-assisted calcium pump in T. gondii and report small molecules with therapeutic potential against toxoplasmosis.

Induction of MASH-like pathogenesis in the Nwd1-/- mouse liver

Endoplasmic reticulum (ER) stores Ca2+ and plays crucial roles in protein folding, lipid transfer, and it's perturbations trigger an ER stress. In the liver, chronic ER stress is involved in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH). Dysfunction of sarco/endoplasmic reticulum calcium ATPase (SERCA2), a key regulator of Ca2+ transport from the cytosol to ER, is associated with the induction of ER stress and lipid droplet formation. We previously identified NACHT and WD repeat domain-containing protein 1 (Nwd1) localized at the ER and mitochondria. However, the physiological significance of Nwd1 outside the brain remains unclear. In this study, we revealed that Nwd1-/- mice exhibited pathological manifestations comparable to MASH. Nwd1 interacts with SERCA2 near ER membranes. Nwd1-/- livers exhibited reduced SERCA2 ATPase activity and a smaller Ca2+ pool in the ER, leading to an exacerbated state of ER stress. These findings highlight the importance of SERCA2 activity mediated by Nwd1 in the pathogenesis of MASH.

In Silico Analysis of Protein-Protein Interactions of Putative Endoplasmic Reticulum Metallopeptidase 1 in Schizosaccharomyces pombe

Ermp1 is a putative metalloprotease from Schizosaccharomyces pombe and a member of the Fxna peptidases. Although their function is unknown, orthologous proteins from rats and humans have been associated with the maturation of ovarian follicles and increased ER stress. This study focuses on proposing the first prediction of PPI by comparison of the interologues between humans and yeasts, as well as the molecular docking and dynamics of the M28 domain of Ermp1 with possible target proteins. As results, 45 proteins are proposed that could interact with the metalloprotease. Most of these proteins are related to the transport of Ca2+ and the metabolism of amino acids and proteins. Docking and molecular dynamics suggest that the M28 domain of Ermp1 could hydrolyze leucine and methionine residues of Amk2, Ypt5 and Pex12. These results could support future experimental investigations of other Fxna peptidases, such as human ERMP1.

Structure and transport mechanism of the human calcium pump SPCA1

Secretory-pathway Ca2+-ATPases (SPCAs) play critical roles in maintaining Ca2+ homeostasis, but the exact mechanism of SPCAs-mediated Ca2+ transport remains unclear. Here, we determined six cryo-electron microscopy (cryo-EM) structures of human SPCA1 (hSPCA1) in a series of intermediate states, revealing a near-complete conformational cycle. With the aid of molecular dynamics simulations, these structures offer a clear structural basis for Ca2+ entry and release in hSPCA1. We found that hSPCA1 undergoes unique conformational changes during ATP binding and phosphorylation compared to other well-studied P-type II ATPases. In addition, we observed a conformational distortion of the Ca2+-binding site induced by the separation of transmembrane helices 4L and 6, unveiling a distinct Ca2+ release mechanism. Particularly, we determined a structure of the long-sought CaE2P state of P-type IIA ATPases, providing valuable insights into the Ca2+ transport cycle. Together, these findings enhance our understanding of Ca2+ transport by hSPCA1 and broaden our knowledge of P-type ATPases.

Cryo-EM structures of human SPCA1a reveal the mechanism of Ca2+/Mn2+ transport into the Golgi apparatus

Secretory pathway Ca²⁺/Mn²⁺ ATPase 1 (SPCA1) actively transports cytosolic Ca²⁺ and Mn²⁺ into the Golgi lumen, playing a crucial role in cellular calcium and manganese homeostasis. Detrimental mutations of the ATP2C1 gene encoding SPCA1 cause Hailey-Hailey disease. Here, using nanobody/megabody technologies, we determined cryo-electron microscopy structures of human SPCA1a in the ATP and Ca²⁺/Mn²⁺-bound (E1-ATP) state and the metal-free phosphorylated (E2P) state at 3.1- to 3.3-Å resolutions. The structures revealed that Ca²⁺ and Mn²⁺ share the same metal ion-binding pocket with similar but notably different coordination geometries in the transmembrane domain, corresponding to the second Ca²⁺-binding site in sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA). In the E1-ATP to E2P transition, SPCA1a undergoes similar domain rearrangements to those of SERCA. Meanwhile, SPCA1a shows larger conformational and positional flexibility of the second and sixth transmembrane helices, possibly explaining its wider metal ion specificity. These structural findings illuminate the unique mechanisms of SPCA1a-mediated Ca²⁺/Mn²⁺ transport.

The Meeting of Micropeptides with Major Ca2+ Pumps in Inner Membranes-Consideration of a New Player, SERCA1b

Calcium is a major signalling bivalent cation within the cell. Compartmentalization is essential for regulation of calcium mediated processes. A number of players contribute to intracellular handling of calcium, among them are the sarco/endoplasmic reticulum calcium ATP-ases (SERCAs). These molecules function in the membrane of ER/SR pumping Ca²⁺ from cytoplasm into the lumen of the internal store. Removal of calcium from the cytoplasm is essential for signalling and for relaxation of skeletal muscle and heart. There are three genes and over a dozen isoforms of SERCA in mammals. These can be potentially influenced by small membrane peptides, also called regulins. The discovery of micropeptides has increased in recent years, mostly because of the small ORFs found in long RNAs, annotated formerly as noncoding (lncRNAs). Several excellent works have analysed the mechanism of interaction of micropeptides with each other and with the best known SERCA1a (fast muscle) and SERCA2a (heart, slow muscle) isoforms. However, the array of tissue and developmental expressions of these potential regulators raises the question of interaction with other SERCAs. For example, the most abundant calcium pump in neonatal and regenerating skeletal muscle, SERCA1b has never been looked at with scrutiny to determine whether it is influenced by micropeptides. Further details might be interesting on the interaction of these peptides with the less studied SERCA1b isoform.

Interaction of Some Asymmetrical Porphyrins with U937 Cell Membranes-In Vitro and In Silico Studies

The aim of the present study was to assess the effects exerted in vitro by three asymmetrical porphyrins (5-(2-hydroxyphenyl)-10,15,20-tris-(4-acetoxy-3-methoxyphenyl)porphyrin, 5-(2-hydroxyphenyl)-10,15,20-tris-(4-acetoxy-3-methoxyphenyl)porphyrinatozinc(II), and 5-(2-hydroxyphenyl)-10,15,20-tris-(4-acetoxy-3-methoxyphenyl)porphyrinatocopper(II)) on the transmembrane potential and the membrane anisotropy of U937 cell lines, using bis-(1,3-dibutylbarbituric acid)trimethine oxonol (DiBAC4(3)) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate (TMA-DPH), respectively, as fluorescent probes for fluorescence spectrophotometry. The results indicate the hyperpolarizing effect of porphyrins in the concentration range of 0.5, 5, and 50 μM on the membrane of human U937 monocytic cells. Moreover, the tested porphyrins were shown to increase membrane anisotropy. Altogether, the results evidence the interaction of asymmetrical porphyrins with the membrane of U937 cells, with potential consequences on cellular homeostasis. Molecular docking simulations, and Molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) free energy of binding calculations, supported the hypothesis that the investigated porphyrinic compounds could potentially bind to membrane proteins, with a critical role in regulating the transmembrane potential. Thus, both the free base porphyrins and the metalloporphyrins could bind to the SERCA2b (sarco/endoplasmic reticulum ATPase isoform 2b) calcium pump, while the metal complexes may specifically interact and modulate calcium-dependent (large conductance calcium-activated potassium channel, Slo1/KCa1.1), and ATP-sensitive (K_ATP), potassium channels. Further studies are required to investigate these interactions and their impact on cellular homeostasis and functionality.

Acute activation of SERCA with CDN1163 attenuates IgE-mediated mast cell activation through selective impairment of ROS and p38 signaling

Mast cells are granulocytic immune sentinels present in vascularized tissues that drive chronic inflammatory mechanisms characteristic of allergic pathologies. IgE-mediated mast cell activation leads to a rapid mobilization of Ca²⁺ from intracellular stores, which is essential for the release of preformed mediators via degranulation and de novo synthesized proinflammatory cytokines and chemokines. Given its potent signaling capacity, the dynamics of Ca²⁺ localization are highly regulated by various pumps and channels controlling cytosolic Ca²⁺ concentrations. Among these is sarco/endoplasmic reticulum Ca²⁺ -ATPase (SERCA), which functions to maintain low cytosolic Ca²⁺ concentrations by actively transporting cytosolic Ca²⁺ ions into the endoplasmic reticulum. In this study, we characterized the role of SERCA in allergen-activated mast cells using IgE-sensitized bone marrow-derived mast cells (BMMCs) treated with the SERCA activating compound, CDN1163, and simultaneously stimulated with allergen through FcεRI under stem cell factor (SCF) potentiation. Acute treatment with CDN1163 was found to attenuate early phase mast cell degranulation along with reactive oxygen species (ROS) production. Additionally, treatment with CDN1163 significantly reduced secretion of IL-6, IL-13, and CCL3, suggesting a role for SERCA in the late phase mast cell response. The protective effects of SERCA activation via CDN1163 treatment on the early and late phase mast cell response may be driven by the selective suppression of p38 MAPK signaling. Together, these findings implicate SERCA as an important regulator of the mast cell response to allergen and suggest SERCA activity may offer therapeutic potential targeting allergic pathologies, warranting further investigation.

Multiple sub-state structures of SERCA2b reveal conformational overlap at transition steps during the catalytic cycle

Sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) pumps Ca²⁺ into the endoplasmic reticulum (ER). Herein, we present cryo-electron microscopy (EM) structures of three intermediates of SERCA2b: Ca²⁺-bound phosphorylated (E1P·2Ca²⁺) and Ca²⁺-unbound dephosphorylated (E2·Pi) intermediates and another between the E2P and E2·Pi states. Our cryo-EM analysis demonstrates that the E1P·2Ca²⁺ state exists in low abundance and preferentially transitions to an E2P-like structure by releasing Ca²⁺ and that the Ca²⁺ release gate subsequently undergoes stepwise closure during the dephosphorylation processes. Importantly, each intermediate adopts multiple sub-state structures including those like the next one in the catalytic series, indicating conformational overlap at transition steps, as further substantiated by atomistic molecular dynamic simulations of SERCA2b in a lipid bilayer. The present findings provide insight into how enzymes accelerate catalytic cycles.

The Pathogenic Mechanism of the ATP2C1 p.Ala109_Gln120del Mutation in Hailey-Hailey Disease

Background

Hailey-Hailey disease (HHD) is an autosomal dominant cutaneous disorder that manifests as repeated blisters and erosions on flexural or intertriginous skin areas. The calcium-transporting ATPase type 2C member 1 gene (ATP2C1) encodes the secretory pathway Ca²⁺/Mn²⁺-ATPase 1 (SPCA1), whose deficiency is responsible for HHD. An ATP2C1 splice-site mutation (c.325-2A>G, p.Ala109_Gln120del) was previously identified in a Han Chinese family with HHD.

Methods

In this study, the identified ATP2C1 splice-site mutation (c.325-2A>G, p.Ala109_Gln120del) was investigated in transfected human embryonic kidney 293 cells to analyze its pathogenic mechanism in HHD patients by using cycloheximide chase assay, CCK8 assay and in silico modeling of SPCA1 mutant.

Results

Cycloheximide chase assay showed that the degradation rate of the SPCA1 mutant was not obviously faster than that of the normal SPCA1. CCK8 assay showed that cell proliferation rates in the wild-type, A109_Q120del, and empty vector control groups all decreased in the gradient Mn²⁺ solutions in a dose-dependent manner. The cell proliferation rate in the wild-type was lower than that in the A109_Q120del and empty vector control (both P < 0.01), indicating overexpression of normal SPCA1 may rather induce Golgi stress, and even cell death. The cell proliferation rate in the A109_Q120del was lower than that in the empty vector control (P < 0.01), indicating that overexpression of the mutated SPCA1 may decrease its detoxification capability. Three-dimensional (3D) structure model of SPCA1 built by SWISS-MODEL and PyMOL showed that absence of the 12 amino acids from p.Ala109 to p.Gln120 in the SPCA1 mutant can cause obviously shortened transmembrane 2, which may affect correct localization of SPCA1 on the Golgi.

Conclusion

These results demonstrate that the ATP2C1 mutation (c.325-2A>G, p.Ala109_Gln120del) may cause impaired SPCA1 capability to detoxify Mn²⁺ and abnormal SPCA1 structure, which reveals a new side for the pathogenesis of HHD.

Cell-To-Cell Communication in the Resistance Vasculature

The arterial vasculature can be divided into large conduit arteries, intermediate contractile arteries, resistance arteries, arterioles, and capillaries. Resistance arteries and arterioles primarily function to control systemic blood pressure. The resistance arteries are composed of a layer of endothelial cells oriented parallel to the direction of blood flow, which are separated by a matrix layer termed the internal elastic lamina from several layers of smooth muscle cells oriented perpendicular to the direction of blood flow. Cells within the vessel walls communicate in a homocellular and heterocellular fashion to govern luminal diameter, arterial resistance, and blood pressure. At rest, potassium currents govern the basal state of endothelial and smooth muscle cells. Multiple stimuli can elicit rises in intracellular calcium levels in either endothelial cells or smooth muscle cells, sourced from intracellular stores such as the endoplasmic reticulum or the extracellular space. In general, activation of endothelial cells results in the production of a vasodilatory signal, usually in the form of nitric oxide or endothelial-derived hyperpolarization. Conversely, activation of smooth muscle cells results in a vasoconstriction response through smooth muscle cell contraction. © 2022 American Physiological Society. Compr Physiol 12: 1-35, 2022.

Structural basis of the conformational and functional regulation of human SERCA2b, the ubiquitous endoplasmic reticulum calcium pump

Sarco/endoplasmic reticulum Ca²⁺ ATPase 2b (SERCA2b), a member of the SERCA family, is expressed ubiquitously and transports Ca²⁺ into the sarco/endoplasmic reticulum using the energy provided by ATP binding and hydrolysis. The crystal structure of SERCA2b in its Ca²⁺ - and ATP-bound (E1∙2Ca²⁺ -ATP) state and cryo-electron microscopy (cryo-EM) structures of the protein in its E1∙2Ca²⁺ -ATP and Ca²⁺ -unbound phosphorylated (E2P) states have provided essential insights into how the overall conformation and ATPase activity of SERCA2b is regulated by the transmembrane helix 11 and the subsequent luminal extension loop, both of which are specific to this isoform. More recently, our cryo-EM analysis has revealed that SERCA2b likely adopts open and closed conformations of the cytosolic domains in the Ca²⁺ -bound but ATP-free (E1∙2Ca²⁺ ) state, and that the closed conformation represents a state immediately prior to ATP binding. This review article summarizes the unique mechanisms underlying the conformational and functional regulation of SERCA2b.

Thapsigargin: key to new host-directed coronavirus antivirals?

Despite the great success of vaccines that protect against RNA virus infections, and the development and clinical use of a limited number of RNA virus-specific drugs, there is still an urgent need for new classes of antiviral drugs against circulating or emerging RNA viruses. To date, it has proved difficult to efficiently suppress RNA virus replication by targeting host cell functions, and there are no approved drugs of this type. This opinion article discusses the recent discovery of a pronounced and sustained antiviral activity of the plant-derived natural compound thapsigargin against enveloped RNA viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Middle East respiratory syndrome coronavirus (MERS-CoV), and influenza A virus. Based on its mechanisms of action, thapsigargin represents a new prototype of compounds with multimodal host-directed antiviral activity.

Cryo-EM analysis provides new mechanistic insight into ATP binding to Ca2+ -ATPase SERCA2b

Sarco/endoplasmic reticulum Ca²⁺ -ATPase (SERCA) 2b is a ubiquitous SERCA family member that conducts Ca²⁺ uptake from the cytosol to the ER. Herein, we present a 3.3 Å resolution cryo-electron microscopy (cryo-EM) structure of human SERCA2b in the E1·2Ca²⁺ state, revealing a new conformation for Ca²⁺ -bound SERCA2b with a much closer arrangement of cytosolic domains than in the previously reported crystal structure of Ca²⁺ -bound SERCA1a. Multiple conformations generated by 3D classification of cryo-EM maps reflect the intrinsically dynamic nature of the cytosolic domains in this state. Notably, ATP binding residues of SERCA2b in the E1·2Ca²⁺ state are located at similar positions to those in the E1·2Ca²⁺ -ATP state; hence, the cryo-EM structure likely represents a preformed state immediately prior to ATP binding. Consistently, a SERCA2b mutant with an interdomain disulfide bridge that locks the closed cytosolic domain arrangement displayed significant autophosphorylation activity in the presence of Ca²⁺ . We propose a novel mechanism of ATP binding to SERCA2b.

Advances in Intracellular Calcium Signaling Reveal Untapped Targets for Cancer Therapy

Intracellular Ca2+ distribution is a tightly regulated process. Numerous Ca2+ chelating, storage, and transport mechanisms are required to maintain normal cellular physiology. Ca2+-binding proteins, mainly calmodulin and calbindins, sequester free intracellular Ca2+ ions and apportion or transport them to signaling hubs needing the cations. Ca2+ channels, ATP-driven pumps, and exchangers assist the binding proteins in transferring the ions to and from appropriate cellular compartments. Some, such as the endoplasmic reticulum, mitochondria, and lysosomes, act as Ca2+ repositories. Cellular Ca2+ homeostasis is inefficient without the active contribution of these organelles. Moreover, certain key cellular processes also rely on inter-organellar Ca2+ signaling. This review attempts to encapsulate the structure, function, and regulation of major intracellular Ca2+ buffers, sensors, channels, and signaling molecules before highlighting how cancer cells manipulate them to survive and thrive. The spotlight is then shifted to the slow pace of translating such research findings into anticancer therapeutics. We use the PubMed database to highlight current clinical studies that target intracellular Ca2+ signaling. Drug repurposing and improving the delivery of small molecule therapeutics are further discussed as promising strategies for speeding therapeutic development in this area.

Nothing Regular about the Regulins: Distinct Functional Properties of SERCA Transmembrane Peptide Regulatory Subunits

The sarco-endoplasmic reticulum calcium ATPase (SERCA) is responsible for maintaining calcium homeostasis in all eukaryotic cells by actively transporting calcium from the cytosol into the sarco-endoplasmic reticulum (SR/ER) lumen. Calcium is an important signaling ion, and the activity of SERCA is critical for a variety of cellular processes such as muscle contraction, neuronal activity, and energy metabolism. SERCA is regulated by several small transmembrane peptide subunits that are collectively known as the “regulins”. Phospholamban (PLN) and sarcolipin (SLN) are the original and most extensively studied members of the regulin family. PLN and SLN inhibit the calcium transport properties of SERCA and they are required for the proper functioning of cardiac and skeletal muscles, respectively. Myoregulin (MLN), dwarf open reading frame (DWORF), endoregulin (ELN), and another-regulin (ALN) are newly discovered tissue-specific regulators of SERCA. Herein, we compare the functional properties of the regulin family of SERCA transmembrane peptide subunits and consider their regulatory mechanisms in the context of the physiological and pathophysiological roles of these peptides. We present new functional data for human MLN, ELN, and ALN, demonstrating that they are inhibitors of SERCA with distinct functional consequences. Molecular modeling and molecular dynamics simulations of SERCA in complex with the transmembrane domains of MLN and ALN provide insights into how differential binding to the so-called inhibitory groove of SERCA—formed by transmembrane helices M2, M6, and M9—can result in distinct functional outcomes.

Ca2+ Regulates ERp57-Calnexin Complex Formation

ERp57, a member of the protein disulfide isomerase family, is a ubiquitous disulfide catalyst that functions in the oxidative folding of various clients in the mammalian endoplasmic reticulum (ER). In concert with ER lectin-like chaperones calnexin and calreticulin (CNX/CRT), ERp57 functions in virtually all folding stages from co-translation to post-translation, and thus plays a critical role in maintaining protein homeostasis, with direct implication for pathology. Here, we present mechanisms by which Ca²⁺ regulates the formation of the ERp57-calnexin complex. Biochemical and isothermal titration calorimetry analyses revealed that ERp57 strongly interacts with CNX via a non-covalent bond in the absence of Ca²⁺. The ERp57-CNX complex not only promoted the oxidative folding of human leukocyte antigen heavy chains, but also inhibited client aggregation. These results suggest that this complex performs both enzymatic and chaperoning functions under abnormal physiological conditions, such as Ca²⁺ depletion, to effectively guide proper oxidative protein folding. The findings shed light on the molecular mechanisms underpinning crosstalk between the chaperone network and Ca²⁺.

The SERCA residue Glu340 mediates interdomain communication that guides Ca2+ transport

We present a crystal structure, functional data, and molecular dynamics (MD) simulations of the sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) mutant E340A. The mutation slows Ca²⁺-binding kinetics, and the structural differences between wild type and E340A indicate that the mutation disrupts a central interdomain “communication hub” governing Ca²⁺ binding/dissociation. MD simulations reveal altered dynamics in regions mediating Ca²⁺ occlusion, a critical step in SERCA’s alternating access mechanism. The mutation stabilizes a more occluded state of the Ca²⁺ sites. The strict conservation of Glu340 among P-type ATPases is the result of its critical role in interdomain communication between the cytosolic headpiece and the transmembrane domain, ensuring a delicate balance between dynamics of ion binding, occlusion, and release—key steps in the transport process.

The sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) is a P-type ATPase that transports Ca²⁺ from the cytosol into the sarco(endo)plasmic reticulum (SR/ER) lumen, driven by ATP. This primary transport activity depends on tight coupling between movements of the transmembrane helices forming the two Ca²⁺-binding sites and the cytosolic headpiece mediating ATP hydrolysis. We have addressed the molecular basis for this intramolecular communication by analyzing the structure and functional properties of the SERCA mutant E340A. The mutated Glu340 residue is strictly conserved among the P-type ATPase family of membrane transporters and is located at a seemingly strategic position at the interface between the phosphorylation domain and the cytosolic ends of 5 of SERCA’s 10 transmembrane helices. The mutant displays a marked slowing of the Ca²⁺-binding kinetics, and its crystal structure in the presence of Ca²⁺ and ATP analog reveals a rotated headpiece, altered connectivity between the cytosolic domains, and an altered hydrogen bonding pattern around residue 340. Supported by molecular dynamics simulations, we conclude that the E340A mutation causes a stabilization of the Ca²⁺ sites in a more occluded state, hence displaying slowed dynamics. This finding underpins a crucial role of Glu340 in interdomain communication between the headpiece and the Ca²⁺-binding transmembrane region.

Pathways for Sensing and Responding to Hydrogen Peroxide at the Endoplasmic Reticulum

The endoplasmic reticulum (ER) has emerged as a source of hydrogen peroxide (H₂O₂) and a hub for peroxide-based signaling events. Here we outline cellular sources of ER-localized peroxide, including sources within and near the ER. Focusing on three ER-localized proteins-the molecular chaperone BiP, the transmembrane stress-sensor IRE1, and the calcium pump SERCA2-we discuss how post-translational modification of protein cysteines by H₂O₂ can alter ER activities. We review how changed activities for these three proteins upon oxidation can modulate signaling events, and also how cysteine oxidation can serve to limit the cellular damage that is most often associated with elevated peroxide levels.