Fungal alkaloid malbrancheamide reorients the lipid binding domain of GRK5

G protein-coupled receptors (GPCRs) are the largest group of receptors involved in various types of signaling. GPCR signaling is regulated via receptor phosphorylation by G protein-coupled receptor kinases 5 (GRK5). Calmodulin (CaM), a universal Ca2+ sensor, inhibits receptor phosphorylation by binding to GRK5. However, the inhibitor malbrancheamide (MBC), which binds at CaM C-lobe, allows for receptor phosphorylation. To understand the phosphorylation mechanism by GRK5, we carried out a MD simulation of the CaM/GRK5 complex in the presence and absence of the MBC inhibitor. The lipid binding domain (LBD) of GRK5 adopted different positions in the presence and absence of inhibitor. Furthermore, the inhibitor MBC restricted the movement of the N-lobe tether (NLT) loop, probably blocking the autophosphorylation of GRK5.Communicated by Ramaswamy H. Sarma.

Identification of Riluzole derivatives as novel calmodulin inhibitors with neuroprotective activity by a joint synthesis, biosensor, and computational guided strategy

The development of new molecules for the treatment of calmodulin related cardiovascular or neurodegenerative diseases is an interesting goal. In this work, we introduce a novel strategy with four main steps: (1) chemical synthesis of target molecules, (2) Förster Resonance Energy Transfer (FRET) biosensor development and in vitro biological assay of new derivatives, (3) Cheminformatics models development and in vivo activity prediction, and (4) Docking studies. This strategy is illustrated with a case study. Firstly, a series of 4-substituted Riluzole derivatives 1-3 were synthetized through a strategy that involves the construction of the 4-bromoriluzole framework and its further functionalization via palladium catalysis or organolithium chemistry. Next, a FRET biosensor for monitoring Ca2+-dependent CaM-ligands interactions has been developed and used for the in vitro assay of Riluzole derivatives. In particular, the best inhibition (80%) was observed for 4-methoxyphenylriluzole 2b. Besides, we trained and validated a new Networks Invariant, Information Fusion, Perturbation Theory, and Machine Learning (NIFPTML) model for predicting probability profiles of in vivo biological activity parameters in different regions of the brain. Next, we used this model to predict the in vivo activity of the compounds experimentally studied in vitro. Last, docking study conducted on Riluzole and its derivatives has provided valuable insights into their binding conformations with the target protein, involving calmodulin and the SK4 channel. This new combined strategy may be useful to reduce assay costs (animals, materials, time, and human resources) in the drug discovery process of calmodulin inhibitors.

Probing calmodulin-NO synthase interactions via site-specific infrared spectroscopy: an introductory investigation

Calmodulin (CaM) binds to a linker between the oxygenase and reductase domains of nitric oxide synthase (NOS) to regulate the functional conformational dynamics. Specific residues on the interdomain interface guide the domain-domain docking to facilitate the electron transfer in NOS. Notably, the docking interface between CaM and the heme-containing oxygenase domain of NOS is isoform specific, which is only beginning to be investigated. Toward advancing understanding of the distinct CaM-NOS docking interactions by infrared spectroscopy, we introduced a cyano-group as frequency-resolved vibrational probe into CaM individually and when associated with full-length and a bi-domain oxygenase/FMN construct of the inducible NOS isoform (iNOS). Site-specific, selective labeling with p-cyano-L-phenylalanine (CNF) by amber suppression of CaM bound to the iNOS has been accomplished by protein coexpression due to the instability of recombinant iNOS protein alone. We introduced CNF at residue 108, which is at the putative CaM-heme (NOS) docking interface. CNF was also introduced at residue 29, which is distant from the docking interface. FT IR data show that the 108 site is sensitive to CaM-NOS complex formation, while insensitivity to its association with the iNOS protein or peptide was observed for the 29 site. Moreover, narrowing of the IR bands at residue 108 suggests the C≡N probe experiences a more limited distribution of environments, indicating side chain restriction apparent for the complex with iNOS. This initial work sets the stage for residue-specific characterizations of structural dynamics of the docked states of NOS proteins.

Vitamin D, Calbindin, and calcium signaling: Unraveling the Alzheimer's connection

Calcium is a ubiquitous second messenger that is indispensable in regulating neurotransmission and memory formation. A precise intracellular calcium level is achieved through the concerted action of calcium channels, and calcium exerts its effect by binding to an array of calcium-binding proteins, including calmodulin (CAM), calcium-calmodulin complex-dependent protein kinase-II (CAMK-II), calbindin (CAL), and calcineurin (CAN). Calbindin orchestrates a plethora of signaling events that regulate synaptic transmission and depolarizing signals. Vitamin D, an endogenous fat-soluble metabolite, is synthesized in the skin upon exposure to ultraviolet B radiation. It modulates calcium signaling by increasing the expression of the calcium-sensing receptor (CaSR), stimulating phospholipase C activity, and regulating the expression of calcium channels such as TRPV6. Vitamin D also modulates the activity of calcium-binding proteins, including CAM and calbindin, and increases their expression. Calbindin, a high-affinity calcium-binding protein, is involved in calcium buffering and transport in neurons. It has been shown to inhibit apoptosis and caspase-3 activity stimulated by presenilin 1 and 2 in AD. Whereas CAM, another calcium-binding protein, is implicated in regulating neurotransmitter release and memory formation by phosphorylating CAN, CAMK-II, and other calcium-regulated proteins. CAMK-II and CAN regulate actin-induced spine shape changes, which are further modulated by CAM. Low levels of both calbindin and vitamin D are attributed to the pathology of Alzheimer's disease. Further research on vitamin D via calbindin-CAMK-II signaling may provide newer insights, revealing novel therapeutic targets and strategies for treatment.

Chlormequat chloride induced activation of calmodulin mediated PI3K/AKT signaling pathway led to impaired sperm quality in pubertal mice

Chlormequat chloride (CCC), as a widely used plant growth regulator, can cause impaired sperm quality and decreased testosterone synthesis in pubertal rats, but the underlying mechanism remains unclear. The purpose of this study was to elucidate the toxicokinetics and tissue distribution of CCC, as well as the possible mechanism of CCC-induced impairment in sperm quality. The concentration of CCC reached its peak 1 h after a single dose (200 mg/kg·bw) administration in mice plasma, and a bimodal phenomenon appeared in the testes, liver, and epididymis. In vivo, 200 mg/kg CCC caused testicular damage and impaired sperm quality in pubertal mice, and the expression of p-tyrosine and GSK3α decreased in cauda epididymidis, sperm and testes. CCC also caused the down-regulation of AKAP4 and the up-regulation of calmodulin (CaM), and activated the PI3K/AKT signaling pathway in the testes. In vitro, CCC reduced the levels of p-tyrosine, AKAP4 and GSK3α, increased the level of CaM and activated the PI3K/AKT signaling pathway in GC-1 cells. CaM antagonist (W-7 hydrochloride) and PI3K inhibitor (LY294002) can effectively improve the expression of GSK3α and AKAP4 by suppressing the PI3K/AKT signaling pathway in GC-1 cells treated with CCC. It was indicated that CCC induced impairment in sperm quality might be partially related to the activation of PI3K/AKT signaling pathway mediated by CaM.

Regulatory sites of CaM-sensitive adenylyl cyclase AC8 revealed by cryo-EM and structural proteomics

Membrane adenylyl cyclase AC8 is regulated by G proteins and calmodulin (CaM), mediating the crosstalk between the cAMP pathway and Ca2+ signalling. Despite the importance of AC8 in physiology, the structural basis of its regulation by G proteins and CaM is not well defined. Here, we report the 3.5 Å resolution cryo-EM structure of the bovine AC8 bound to the stimulatory Gαs protein in the presence of Ca2+/CaM. The structure reveals the architecture of the ordered AC8 domains bound to Gαs and the small molecule activator forskolin. The extracellular surface of AC8 features a negatively charged pocket, a potential site for unknown interactors. Despite the well-resolved forskolin density, the captured state of AC8 does not favour tight nucleotide binding. The structural proteomics approaches, limited proteolysis and crosslinking mass spectrometry (LiP-MS and XL-MS), allowed us to identify the contact sites between AC8 and its regulators, CaM, Gαs, and Gβγ, as well as to infer the conformational changes induced by these interactions. Our results provide a framework for understanding the role of flexible regions in the mechanism of AC regulation.

A PDZ scaffolding/CaM-mediated pathway in Cryptochrome signaling

Cryptochromes are cardinal constituents of the circadian clock, which orchestrates daily physiological rhythms in living organisms. A growing body of evidence points to their participation in pathways that have not traditionally been associated with circadian clock regulation, implying that cryptochromes may be subject to modulation by multiple signaling mechanisms. In this study, we demonstrate that human CRY2 (hCRY2) forms a complex with the large, modular scaffolding protein known as Multi-PDZ Domain Protein 1 (MUPP1). This interaction is facilitated by the calcium-binding protein Calmodulin (CaM) in a calcium-dependent manner. Our findings suggest a novel cooperative mechanism for the regulation of mammalian cryptochromes, mediated by calcium ions (Ca2+ ) and CaM. We propose that this Ca2+ /CaM-mediated signaling pathway may be an evolutionarily conserved mechanism that has been maintained from Drosophila to mammals, most likely in relation to its potential role in the broader context of cryptochrome function and regulation. Further, the understanding of cryptochrome interactions with other proteins and signaling pathways could lead to a better definition of its role within the intricate network of molecular interactions that govern circadian rhythms.

Arabidopsis CML13 and CML14 Have Essential and Overlapping Roles in Plant Development

Calmodulin (CaM)-like proteins (CMLs) are the largest family of calcium-binding proteins in plants, yet the functions of most CMLs are unknown. Arabidopsis CML13 and CML14 are closely related paralogs that interact with the isoleucine-glutamine (IQ) domains of myosins, IQ-domain proteins and CaM-binding transcription activators (CAMTAs). Here, we explored the physiological roles of CML13 and CML14 during development by using dexamethasone (Dex)-inducible RNA silencing to suppress either CML13 or CML14 transcript levels. In the absence of inducible suppression, CML13- and CML14-RNA-interference lines were indistinguishable from wild-type (WT) plants throughout development. In contrast, induction of silencing treatment led to rapid increases in RNA-hairpin production that correlated with a targeted reduction in CML13 or CML14 transcript levels and a range of developmental and morphological effects. RNA-suppression treatment did not impair the germination of CML13- or 14-RNA-interference lines, but these seedlings were chlorotic, displayed high mortality and failed to achieve seedling establishment. Under Dex treatment, seeds of CML13- and CML14-RNA-interference lines exhibited differential sensitivity to exogenous ABA compared to WT seeds. Induced RNA suppression of mature plants led to reduced silique length, shorter roots and rapid leaf senescence in CML13- and 14-RNA-interference plants, which correlated with increased gene expression of the senescence marker Senescence-Associated Gene13 (SAG13). Plants induced for RNA suppression at 2 weeks post-germination exhibited a much stronger phenotype than treatment of 3-, 4- or 5-week-old plants. Collectively, our data indicate that both CML13 and CML14 are essential for normal development and function across a broad range of tissues and developmental stages.

High-throughput drug screen identifies calcium and calmodulin inhibitors that reduce JCPyV infection

JC polyomavirus (JCPyV) is a nonenveloped, double-stranded DNA virus that infects the majority of the population. Immunocompetent individuals harbor infection in their kidneys, while severe immunosuppression can result in JCPyV spread to the brain, causing the neurodegenerative disease progressive multifocal leukoencephalopathy (PML). Due to a lack of approved therapies to treat JCPyV and PML, the disease results in rapid deterioration, and is often fatal. In order to identify potential antiviral treatments for JCPyV, a high-throughput, large-scale drug screen was performed using the National Institutes of Health Clinical Collection (NCC). Drugs from the NCC were tested for inhibitory effects on JCPyV infection, and drugs from various classes that reduced JCPyV infection were identified, including receptor agonists and antagonists, calcium signaling modulators, and enzyme inhibitors. Given the role of calcium signaling in viral infection including Merkel cell polyomavirus and simian virus 40 polyomavirus (SV40), calcium signaling inhibitors were further explored for the capacity to impact JCPyV infection. Calcium and calmodulin inhibitors trifluoperazine (TFP), W-7, tetrandrine, and nifedipine reduced JCPyV infection, and TFP specifically reduced viral internalization. Additionally, TFP and W-7 reduced infection by BK polyomavirus, SV40, and SARS-CoV-2. These results highlight specific inhibitors, some FDA-approved, for the possible treatment and prevention of JCPyV and several other viruses, and further illuminate the calcium and calmodulin pathway as a potential target for antiviral drug development.

Hsc70 phosphorylation patterns and calmodulin regulate AP2 Clathrin-Coated-Vesicle life span for cell adhesion protein transport

AP2 forms AP2 CCV with clathrin and over 60 additional coat proteins. Due to this complexity, we have a limited understanding of CCV life cycle regulation. Synapses contain canonical AP2 CCV, canCCV, and more stable, thereby longer lived, AP2 CCV. The more stable AP2 CCV can be distinguished from canCCV due to the stable binding of Hsc70 to clathrin. The AP1/σ1B complex knockout leads to impaired synaptic vesicle recycling and altered endosomal protein sorting. This causes as a secondary phenotype the twofold upregulation of endocytosis by canCCV and by more stable AP2 CCV. These stable CCV are more stabilized than their wt counterpart, hence stCCV. They have less of the uncoating proteins synaptojanin1 and Hsc70, and more of the coat stabilizing AAK1. Hsc70 clathrin dissociation activity is regulated by complex phosphorylation patterns. Two major groups of hyper- and of hypo-phosphorylated Hsc70 proteins are formed. The latter are enriched in wt stable CCV and stabilized stCCV. Hsc70 T265 phosphorylation regulates binding of CaM/Ca2+. CaM/Ca2+ binding to the T265 domain blocks Hsc70 homodimerization and its concentration in stCCV required for clathrin disassembly. Kinases DYRK1A and CaMK-IIδ can phosphorylate T265 preventing CaM/Ca2+ binding. Their and the levels of STK38L and STK39/Cab39, which are able to phosphorylate additional Hsc70 residues are reduced in stCCV. The stCCV pathway sorts specifically the cell adhesion proteins CHL1 and Neurocan, supporting our model of that the stCCV pathway fulfills specific functions in synaptic plasticity.

Allosteric changes in protein stability and dynamics as pathogenic mechanism for calmodulin variants not affecting Ca2+ coordinating residues

Mutations in the small, calcium-sensing, protein calmodulin cause cardiac arrhythmia and can ultimately prove lethal. Here, we report the impact of the G113R variant on the structure and dynamics of the calmodulin molecule, both in the presence and in the absence of calcium. We show that the mutation introduces minor changes into the structure of calmodulin and that it changes the thermostability and thus the degree of foldedness at human body temperature. The mutation also severely impacts the intramolecular mobility of calmodulin, especially in the apo form. Glycine 113 acts as an alpha-helical C-capping residue in both apo/ - and Ca2+/calmodulin, but its exchange to arginine has very different effects on the apo and Ca2+ forms. The majority of arrhythmogenic calmodulin variants identified affects residues in the Ca2+ coordinating loops of the two C-domain EF-Hands, causing a 'direct impact on Ca2+ binding'. However, G113R lies outside a Ca2+ coordinating loop and acts differently and more similar to the previously characterized arrhythmogenic N53I. Therefore, we suggest that altered apo/CaM dynamics may be a novel general disease mechanism, defining low-calcium target affinity - or Ca2+ binding kinetics - critical for timely coordination of essential ion-channels in the excitation-contraction cycle.

Genome-wide analyses of calmodulin and calmodulin-like proteins in the halophyte Nitraria sibirica reveal their involvement in response to salinity, drought and cold stress

The calmodulin (CaM) and calmodulin-like (CML) proteins are major calcium sensors that play a critical role in environmental stimulus response in plants. Nevertheless, the CaM/CML proteins from the specific plants with extreme tolerance to abiotic stresses remained so far uncharacterized. In this study, 66 candidate proteins (three NsCaMs and sixty-three NsCMLs) were identified from the halophyte Nitraria sibirica, which can withstand an extreme salinity. Bioinformatic analysis of upstream cis-acting elements predicted the potential involvement of NsCaM/CMLs in abiotic stress responses and various hormone responses. Additionally, the Nitraria sibirica transcriptome revealed that 17 and 7 NsCMLs were significantly upregulated under 100 mM or 400 mM NaCl treatment. Transcription of most salt-responsive genes was similarly upregulated under cold stress, yet downregulated under drought treatment. Moreover, predictive subcellular localization analysis suggested that the stress-responsive NsCML proteins mainly localize at the cellular membrane and within the nucleus. Furthermore, transgenic overexpression of two NsCMLs (NISI03G1136 and NISI01G1645) was found to mitigate H2O2 accumulation caused by salt stress. These results provide insights into the potential function of Nitraria sibirica CaM/CML proteins, which could aid the investigation of molecular mechanisms of extreme tolerance to abiotic stresses in halophytes.

Immobilization of azide-functionalized proteins to micro- and nanoparticles directly from cell lysate

Immobilization of proteins and enzymes on solid supports has been utilized in a variety of applications, from improved protein stability on supported catalysts in industrial processes to fabrication of biosensors, biochips, and microdevices. A critical requirement for these applications is facile yet stable covalent conjugation between the immobilized and fully active protein and the solid support to produce stable, highly bio-active conjugates. Here, we report functionalization of solid surfaces (gold nanoparticles and magnetic beads) with bio-active proteins using site-specific and biorthogonal labeling and azide-alkyne cycloaddition, a click chemistry. Specifically, we recombinantly express and selectively label calcium-dependent proteins, calmodulin and calcineurin, and cAMP-dependent protein kinase A (PKA) with N-terminal azide-tags for efficient conjugation to nanoparticles and magnetic beads. We successfully immobilized the proteins on to the solid supports directly from the cell lysate with click chemistry, forgoing the step of purification. This approach is optimized to yield low particle aggregation and high levels of protein activity post-conjugation. The entire process enables streamlined workflows for bioconjugation and highly active conjugated proteins.

Calmodulin Mutations in Human Disease

Calcium ions (Ca²⁺) are the basis of a unique and potent array of cellular responses. Calmodulin (CaM) is a small but vital protein that is able to rapidly transmit information about changes in Ca²⁺ concentrations to its regulatory targets. CaM plays a critical role in cellular Ca²⁺ signaling, and interacts with a myriad of target proteins. Ca²⁺-dependent modulation by CaM is a major component of a diverse array of processes, ranging from gene expression in neurons to the shaping of the cardiac action potential in heart cells. Furthermore, the protein sequence of CaM is highly evolutionarily conserved, and identical CaM proteins are encoded by three independent genes (CALM1-3) in humans. Mutations within any of these three genes may lead to severe cardiac deficits including severe long QT syndrome (LQTS) and/or catecholaminergic polymorphic ventricular tachycardia (CPVT). Research into disease-associated CaM variants has identified several proteins modulated by CaM that are likely to underlie the pathogenesis of these calmodulinopathies, including the cardiac L-type Ca²⁺ channel (LTCC) Ca_V1.2, and the sarcoplasmic reticulum Ca²⁺ release channel, ryanodine receptor 2 (RyR2). Here, we review the research that has been done to identify calmodulinopathic CaM mutations and evaluate the mechanisms underlying their role in disease.

Synergistic modulation of neuroendocrine-inflammation pathway by microRNAs facilitates intertidal adaptation of molluscs

Neuroendocrine-immune system is an evolution-conserved regulatory network in maintaining the homeostasis of animals. While knowledge on the roles of neuroendocrine-immune system in the disease and stress responses of organisms is growing, the ecological roles of neuroendocrine-immune system, especially how it shapes the unique lifestyle of organisms remain insufficiently investigated. As an endemic and dominant mollusc in intertidal region, oysters have evolved with a primitive neuroendocrine-immune system and with a sessile lifestyle. Recently, a novel neuroendocrine-immune pathway, Ca2+/calmodulin (CaM)-nitrite oxide synthase (NOS)/nitrite oxide (NO)-tumor necrosis factor (TNF) pathway, is identified in oysters and found altered dynamically during aerial exposure, one common but challenging stresses for intertidal organisms and a decisive factor shaping their habitat. Since the pathway proves fatal in prolonged aerial exposure, we hypothesized that the activation/deactivation of pathway could be strictly modulated in adaptation to the sessile lifestyle of oysters. Here, a synergistic modulation on the Ca2+/CaM-NOS/NO-TNF pathway by four members of miR-92 family and two oyster-specific miRNAs was identified, which further hallmarks the resilience and survival strategy of oysters to aerial exposure. Briefly, these six miRNAs were down-regulating CgCaM24243 post-transcriptionally and deactivating the pathway during the early-stage of stress. However, a robust recession of these miRNAs occurred at the late-stage of stress, resulting in the reactivation of pathway and overwhelming accumulation of cytokines. These results demonstrated a complicated interaction between miRNAs and ancient neuroendocrine-immune system, which facilitates the environmental adaptation of intertidal oysters and provides novel insight on the function and evolution of neuroendocrine-immune system in ecological context.

Review on nitric oxide at the forefront of rapid systemic signaling in mitigation of salinity stress in plants: Crosstalk with calcium and hydrogen peroxide

Soil salinity is a global issue that limits plant growth in agricultural fields and contributes to food crisis. Salt stressors impede plant's ionic, osmotic, and oxidative balance, as well as a variety of physiological functions. Exposure to salinity stress manifest considerable ROS clustering, entailing modification in performance of various organelles. To deal with salinity, plants use a variety of coping strategies, such as osmoregulation, ion-homeostasis, increased antioxidant synthesis, and so on. Nitric oxide (NO) is a pivotal signalling molecule that helps facilitate salt stress-induced physiological plant responses. A variety of evidences point to NO being produced under similar stress conditions and with similar kinetics as hydrogen peroxide (H2O2). The interplay between H2O2 and NO has important functional implications for modulating plant transduction processes. Besides, NO and calcium (Ca2+)-dependent pathways also have some connection in salt stress response mechanisms. Extensive crosstalk between NO and Ca2+ signalling pathways is investigated, and it suggests that almost every type of Ca2+ channel is under the tight control of NO, and NO acts as a Ca2+ mobilising compound and aids in signal reliance. The review provides insights into understanding recent advances regarding NO's, Ca2+ and H2O2 role in salt stress reduction with entwine signaling mechanisms.

Effect of nano-calcium on carotenoid and anthocyanin contents of nectarine fruit

Increasing the carotenoid content of nectarine (Prunus persica var. nucipersica) is of great significance for improving its quality and economic value. A two years study was carried out on 'Shuguang' nectarine to evaluate the effect of calcium chloride (Cl-Ca) and L-aspartic acid nano calcium [Ca (L-asp) - NPs] (nano-Ca) on carotenoid accumulation. The results show that both Cl-Ca and nano-Ca could increase the carotenoid content of nectarine fruit flesh, but the effect of nano-Ca was more significant. Nano-Ca is more easily absorbed by nectarine leaves and fruits, which improves the calmodulin activity of leaves, peel and flesh, and up-regulates the expression of carotenoid synthesis-related genes PpPSY, PpPDS, PpZDS, PpLCY-B, PpCHY-B and PpZEP. Nano-Ca also significantly up-regulated the expression of sucrose synthesis related genes PpSUS1 and PpSUS3 in leaves and sucrose transport related genes PpSUT2 and PpSUT4 in stem phloem, promoting the transport of more photosynthetic products to fruits, providing raw materials for carotenoid synthesis, and increasing the content of total sugars and ascorbic acid (Vc). In addition, nano-Ca can also up-regulate the expression levels of PpMYB10.1 and PpUFGT and promote total anthocyanins accumulation in peel. The results of our study will be useful for clarifying how nano-fertilizer improve the fruit quality of nectarine.

Activation of TRPV1 Channels Inhibits the Release of Acetylcholine and Improves Muscle Contractility in Mice

TRPV1 represents a non-selective transient receptor potential cation channel found not only in sensory neurons, but also in motor nerve endings and in skeletal muscle fibers. However, the role of TRPV1 in the functioning of the neuromuscular junction has not yet been fully established. In this study, the Levator Auris Longus muscle preparations were used to assess the effect of pharmacological activation of TRPV1 channels on neuromuscular transmission. The presence of TRPV1 channels in the nerve terminal and in the muscle fiber was confirmed by immunohistochemistry. It was verified by electrophysiology that the TRPV1 channel agonist capsaicin inhibits the acetylcholine release, and this effect was completely absent after preliminary application of the TRPV1 channel blocker SB 366791. Nerve stimulation revealed an increase of amplitude of isometric tetanic contractions upon application of capsaicin which was also eliminated after preliminary application of SB 366791. Similar data were obtained during direct muscle stimulation. Thus, pharmacological activation of TRPV1 channels affects the functioning of both the pre- and postsynaptic compartment of the neuromuscular junction. A moderate decrease in the amount of acetylcholine released from the motor nerve allows to maintain a reserve pool of the mediator to ensure a longer signal transmission process, and an increase in the force of muscle contraction, in its turn, also implies more effective physiological muscle activity in response to prolonged stimulation. This assumption is supported by the fact that when muscle was indirect stimulated with a fatigue protocol, muscle fatigue was attenuated in the presence of capsaicin.

On the role of calcium diffusion and its rapid buffering in intraflagellar signaling

We have considered the realistic mechanism of rapid Ca2+ (calcium ion) buffering within the wave of calcium ions progressing along the flagellar axoneme. This buffering is an essential part of the Ca2+ signaling pathway aimed at controlling the bending dynamics of flagella. It is primarily achieved by the mobile region of calmodulin molecules and by stationary calaxin, as well as by the part of calmodulin bound to calcium/calmodulin-dependent kinase II and kinase C. We derived and elaborated a model of Ca2+ diffusion within a signaling wave in the presence of these molecules which rapidly buffer Ca2+. This approach has led to a single nonlinear transport equation for the Ca2+ wave that contains the effects brought about by both as necessary buffers for signaling. The presence of mobile buffer calmodulin gives rise to a transport equation that is not strictly diffusive but also exhibits a sink-like effect. We solved straightforwardly the final transport equation in an analytical framework and obtained the implied function of calcium concentration. The effective diffusion coefficient depends on local Ca2+ concentration. It is plausible that these buffers' presence can impact Ca2+ wave speed and shape, which are essential for decoding Ca2+ signaling in flagella. We present the solution of the transport equation for a few specified cases with physiologically reasonable sets of parameters involved.

Ca2+ signaling and the Hippo pathway: Intersections in cellular regulation

The Hippo signaling pathway is a master regulator of organ size and tissue homeostasis. Hippo integrates a broad range of cellular signals to regulate numerous processes, such as cell proliferation, differentiation, migration and mechanosensation. Ca2+ is a fundamental second messenger that modulates signaling cascades involved in diverse cellular functions, some of which are also regulated by the Hippo pathway. Studies published over the last five years indicate that Ca2+ can influence core Hippo pathway components. Nevertheless, comprehensive understanding of the crosstalk between Ca2+ signaling and the Hippo pathway, and possible mechanisms through which Ca2+ regulates Hippo, remain to be elucidated. In this review, we summarize the multiple intersections between Ca2+ and the Hippo pathway and address the biological consequences.

Role of myristoylation in modulating PCaP1 interaction with calmodulin

Plasma membrane-associated Cation-binding Protein 1 (PCaP1) belongs to the plant-unique DREPP protein family with largely unknown biological functions but ascertained roles in plant development and calcium (Ca2+) signaling. PCaP1 is anchored to the plasma membrane via N-myristoylation and a polybasic cluster, and its N-terminal region can bind Ca2+/calmodulin (CaM). However, the molecular determinants of PCaP1-Ca2+-CaM interaction and the functional impact of myristoylation in the complex formation and Ca2+ sensitivity of CaM remained to be elucidated. Herein, we investigated the direct interaction between Arabidopsis PCaP1 (AtPCaP1) and CaM1 (AtCaM1) using both myristoylated and non-myristoylated peptides corresponding to the N-terminal region of AtPCaP1. ITC analysis showed that AtCaM1 forms a high affinity 1:1 complex with AtPCaP1 peptides and the interaction is strictly Ca2+-dependent. Spectroscopic and kinetic Ca2+ binding studies showed that the myristoylated peptide dramatically increased the Ca2+-binding affinity of AtCaM1 and slowed the Ca2+ dissociation rates from both the C- and N-lobes, thus suggesting that the myristoylation modulates the mechanism of AtPCaP1 recognition by AtCaM1. Furthermore, NMR and CD spectroscopy revealed that the structure of both the N- and C-lobes of Ca2+-AtCaM1 changes markedly in the presence of the myristoylated AtPCaP1 peptide, which assumes a helical structure in the final complex. Overall, our results indicate that AtPCaP1 biological function is strictly related to the presence of multiple ligands, i.e., the myristoyl moiety, Ca2+ ions and AtCaM1 and only a full characterization of their equilibria will allow for a complete molecular understanding of the putative role of PCaP1 as signal protein.

Clinical presentation of calmodulin mutations: the International Calmodulinopathy Registry

AIMS

Calmodulinopathy due to mutations in any of the three CALM genes (CALM1-3) causes life-threatening arrhythmia syndromes, especially in young individuals. The International Calmodulinopathy Registry (ICalmR) aims to define and link the increasing complexity of the clinical presentation to the underlying molecular mechanisms.

METHODS AND RESULTS

The ICalmR is an international, collaborative, observational study, assembling and analysing clinical and genetic data on CALM-positive patients. The ICalmR has enrolled 140 subjects (median age 10.8 years [interquartile range 5-19]), 97 index cases and 43 family members. CALM-LQTS and CALM-CPVT are the prevalent phenotypes. Primary neurological manifestations, unrelated to post-anoxic sequelae, manifested in 20 patients. Calmodulinopathy remains associated with a high arrhythmic event rate (symptomatic patients, n = 103, 74%). However, compared with the original 2019 cohort, there was a reduced frequency and severity of all cardiac events (61% vs. 85%; P = .001) and sudden death (9% vs. 27%; P = .008). Data on therapy do not allow definitive recommendations. Cardiac structural abnormalities, either cardiomyopathy or congenital heart defects, are present in 30% of patients, mainly CALM-LQTS, and lethal cases of heart failure have occurred. The number of familial cases and of families with strikingly different phenotypes is increasing.

CONCLUSION

Calmodulinopathy has pleiotropic presentations, from channelopathy to syndromic forms. Clinical severity ranges from the early onset of life-threatening arrhythmias to the absence of symptoms, and the percentage of milder and familial forms is increasing. There are no hard data to guide therapy, and current management includes pharmacological and surgical antiadrenergic interventions with sodium channel blockers often accompanied by an implantable cardioverter-defibrillator.

Evolution and diversification of CaM/CML gene family in green plants

Calmodulin (CaM) and calmodulin-like (CML) proteins are crucial Ca2+ sensors, which are widely involved in different biological processes of plants, including their growth and development, and stress responses. However, the origin and evolution of the CaM/CML gene family in plants remain elusive. In this study, 2133 CaM and 23094 CML genes were identified from the 1000 plants project (1 KP) species and the sequenced plants, covering algae, mosses, monilophytes, lycophytes, flowering plants, and all other green plant branches. Analysis showed that the size of the CML subfamily was correlated with the genome size of corresponding plant species, as well as the total gene number in the genome. Moreover, with the evolution from algae to angiosperms, the number of CML genes in plants increased gradually which could have been driven mainly by genome-wide segmental duplication events, while the number of CaMs remained basically stable at 2-3. Phylogenetic analysis demonstrated that CaM first appeared in green algae, while CML appeared earlier and has already been presented in dinoflagellates. Further analysis showed that the number and sequence of EF-hand domain in CaMs are highly conserved, while those of CMLs are diverse among different plant taxa. Expression analysis revealed that the expression level of CaMs was generally higher than that of CMLs, indicating that the high-expression genes have essential functions, while the low-expression genes are the main reasons for the functional diversity of the CaM/CML gene family in plants. The results might contribute to understanding the evolution of CaM/CML genes as well as their molecular functions.

Dantrolene improves left ventricular diastolic property in mineralcorticoid-salt-induced hypertensive rats

Left ventricular (LV) diastolic dysfunction is increasingly common in heart failure with preserved ejection fraction (HFpEF), and new drug therapy is desired. We recently reported that dantrolene (DAN) attenuates pressure-overload induced hypertrophic signaling through stabilization of tetrameric structure of cardiac ryanodine receptor (RyR2). Because cardiac hypertrophy substantially affects LV diastolic properties, we investigated the effect of DAN on LV diastolic properties in mineralocorticoid-salt-induced hypertensive rat model exhibiting the HFpEF phenotype. Male Sprague-Dawley (SD) rats (8 weeks old) received an uninephrectomy (UNX), subcutaneous implantation of a 200 mg pellet of deoxycorticosterone acetate (DOCA), and 0.9% NaCl water (UNX + DOCA-salt). UNX, a control pellet, and water without NaCl served as controls (UNX control). The effect of oral administration of 100 mg/kg/d DAN was examined in UNX control and UNX + DOCA-salt groups (UNX + DAN and UNX + DOCA-salt + DAN). UNX + DOCA-salt treatment resulted in mild hypertension. Chronic administration of DAN to UNX + DOCA-salt rats (UNX + DOCA-salt + DAN) did not affect blood pressure. DAN treatment increased the mitral annular early relaxation velocity in the UNX + DOCA-salt group. The size of cardiomyocytes increased in the UNX + DOCA-salt group, whereas the increase was suppressed by DAN treatment. LV fibrotic area was significantly smaller in the UNX + DOCA-salt + DAN group than in the UNX + DOCA-salt group (2.0 ± 0.2% vs 4.0 ± 0.4%). The LV chamber stiffness significantly increased in the UNX + DOCA-salt group, whereas the increase was suppressed by DAN treatment. DAN treatment normalized the CaM-RyR2 interaction and inhibited aberrant Ca²⁺ release. DAN improved left ventricular diastolic properties with respect to both myocardial relaxation and chamber stiffness. DAN may be a new treatment option for HFpEF.

Vitamin D and calcium co-therapy mitigates pre-established cadmium nephropathy by regulating renal calcium homeostatic molecules and improving anti-oxidative and anti-inflammatory activities in rat

BACKGROUND

Cadmium (Cd) is a major environmental pollutant and chronic toxicity could induce nephropathy by increasing renal oxidative stress and inflammation. Although vitamin D (VD) and calcium (Ca) prophylactic treatments attenuated Cd-induced cell injury, none of the prior studies measure their renoprotective effects against pre-established Cd-nephropathy.

AIMS

To measure the alleviating effects of VD and/or Ca single and dual therapies against pre-established nephrotoxicity induced by chronic Cd toxicity prior to treatment initiation.

METHODS

Forty male adult rats were allocated into: negative controls (NC), positive controls (PC), Ca, VD and VC groups. The study lasted for eight weeks and all animals, except the NC, received CdCl₂ in drinking water (44 mg/L) throughout the study. Ca (100 mg/kg) and/or VD (350 IU/kg) were given (five times/week) during the last four weeks to the designated groups. Subsequently, the expression of transforming growth factor-β (TGF-β1), inducible nitric oxide synthase (iNOS), neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), VD synthesising (Cyp27b1) and catabolizing (Cyp24a1) enzymes with VD receptor (VDR) and binding protein (VDBP) was measured in renal tissues. Similarly, renal expression of Ca voltage-dependent channels (Ca_V1.1/Ca_V3.1), store-operated channels (RyR1/ITPR1), and binding proteins (CAM/CAMKIIA/S100A1/S100B) were measured. Serum markers of renal function alongside several markers of oxidative stress (MDA/H₂O₂/GSH/GPx/CAT) and inflammation (IL-6/TNF-α/IL-10) together with renal cell apoptosis and expression of caspase-3 were also measured.

RESULTS

The PC group exhibited hypovitaminosis D, hypocalcaemia, hypercalciuria, proteinuria, reduced creatinine clearance, and increased renal apoptosis/necrosis with higher caspase-3 expression. Markers of renal tissue damage (TGF-β1/iNOS/NGAL/KIM-1), oxidative stress (MDA/H₂O₂), and inflammation (TNF-α/IL-1β/IL-6) increased, whilst the antioxidants (GSH/GPx/CAT) and IL-10 decreased, in the PC group. The PC renal tissues also showed abnormal expression of Cyp27b1, Cyp24a1, VDR, and VDBP, alongside Ca-membranous (Ca_V1.1/Ca_V3.1) and store-operated channels (RyR1/ITPR1) and cytosolic Ca-binding proteins (CAM/CAMKIIA/S100A1/S100B). Although VD was superior to Ca monotherapy, their combination revealed the best mitigation effects by attenuating serum and renal tissue Cd concentrations, inflammation and oxidative stress, alongside modulating the expression of VD/Ca-molecules.

CONCLUSIONS

This study is the first to show improved alleviations against Cd-nephropathy by co-supplementing VD and Ca, possibly by better regulation of Ca-dependent anti-oxidative and anti-inflammatory actions.

Ionic displacement of Ca2+ by Pb2+ in calmodulin is affected by arrhythmia-associated mutations

Lead is a highly toxic metal that severely perturbs physiological processes even at sub-micromolar levels, often by disrupting the Ca²⁺ signaling pathways. Recently, Pb²⁺-associated cardiac toxicity has emerged, with potential involvement of both the ubiquitous Ca²⁺ sensor protein calmodulin (CaM) and ryanodine receptors. In this work, we explored the hypothesis that Pb²⁺ contributes to the pathological phenotype of CaM variants associated with congenital arrhythmias. We performed a thorough spectroscopic and computational characterization of CaM conformational switches in the co-presence of Pb²⁺ and four missense mutations associated with congenital arrhythmias, namely N53I, N97S, E104A and F141L, and analyzed their effects on the recognition of a target peptide of RyR2. When bound to any of the CaM variants, Pb²⁺ is difficult to displace even under equimolar Ca²⁺ concentrations, thus locking all CaM variants in a specific conformation, which exhibits characteristics of coiled-coil assemblies. All arrhythmia-associated variants appear to be more susceptible to Pb²⁺ than WT CaM, as the conformational transition towards the coiled-coil conformation occurs at lower Pb²⁺, regardless of the presence of Ca²⁺, with altered cooperativity. The presence of arrhythmia-associated mutations specifically alters the cation coordination of CaM variants, in some cases involving allosteric communication between the EF-hands in the two domains. Finally, while wild type CaM increases the affinity for the RyR2 target in the presence of Pb²⁺, no specific pattern could be detected for all other variants, ruling out a synergistic effect of Pb²⁺ and mutations in the recognition process.

Characterization of CpCaM, a protein potentially involved in the growth of Cryptosporidium parvum

Cryptosporidium parvum is an important apicomplexan parasite causing severe diarrhea in both humans and animals. Calmodulin (CaM), a multifunctional and universal calcium-binding protein, contributes to the growth and development of apicomplexan parasites, but the role of CaM in C. parvum remains unknown. In this study, the CaM of C. parvum encoded by the cgd2_810 gene was expressed in Escherichia coli, and the biological functions of CpCaM were preliminarily investigated. The transcriptional level of the cgd2_810 gene peaked at 36 h post infection (pi), and the CpCaM protein was mainly located around the nucleus of the whole oocysts, in the middle of sporozoites and around the nucleus of merozoites. Anti-CpCaM antibody reduced the invasion of C. parvum sporozoites by 30.69%. The present study indicates that CpCaM is potentially involved in the growth of C. parvum. Results of the study expand our knowledge on the interaction between host and Cryptosporidium.

Life-threatening arrhythmogenic CaM mutations disrupt CaM binding to a distinct RyR2 CaM-binding pocket

Calmodulin (CaM) modulates the activity of several proteins that play a key role in excitation-contraction coupling (ECC). In cardiac muscle, the major binding partner of CaM is the type-2 ryanodine receptor (RyR2) and altered CaM binding contributes to defects in sarcoplasmic reticulum (SR) calcium (Ca²⁺) release. Many genetic studies have reported a series of CaM missense mutations in patients with a history of severe arrhythmogenic cardiac disorders. In the present study, we generated four missense CaM mutants (CaM^N98I, CaM^D132E, CaM^D134H and CaM^Q136P) and we used a CaM-RyR2 co-immunoprecipitation and a [³H]ryanodine binding assay to directly compare the relative RyR2-binding of wild type and mutant CaM proteins and to investigate the functional effects of these CaM mutations on RyR2 activity. Furthermore, isothermal titration calorimetry (ITC) experiments were performed to investigate and compare the interactions of the wild-type and mutant CaM proteins with various synthetic peptides located in the well-established RyR2 CaM-binding region (3584-3602aa), as well as another CaM-binding region (4255-4271aa) of human RyR2. Our data revealed that all four CaM mutants displayed dramatically reduced RyR2 interaction and defective modulation of [³H]ryanodine binding to RyR2, regardless of LQTS or CPVT association. Moreover, our isothermal titration calorimetry ITC data suggest that RyR2 3584-3602aa and 4255-4271aa regions interact with significant affinity with wild-type CaM, in the presence and absence of Ca²⁺, two regions that might contribute to a putative intra-subunit CaM-binding pocket. In contrast, screening the interaction of the four arrhythmogenic CaM mutants with two synthetic peptides that correspond to these RyR2 regions, revealed disparate binding properties and signifying differential mechanisms that contribute to reduced RyR2 association.

RyR2-targeting therapy prevents left ventricular remodeling and ventricular tachycardia in post-infarction heart failure

BACKGROUND

Dantrolene binds to the Leu⁶⁰¹-Cys⁶²⁰ region of the N-terminal domain of cardiac ryanodine receptor (RyR2), which corresponds to the Leu⁵⁹⁰-Cys⁶⁰⁹ region of the skeletal ryanodine receptor, and suppresses diastolic Ca²⁺ leakage through RyR2.

OBJECTIVE

We investigated whether the chronic administration of dantrolene prevented left ventricular (LV) remodeling and ventricular tachycardia (VT) after myocardial infarction (MI) by the same mechanism with the mutation V3599K of RyR2, which indicated that the inhibition of diastolic Ca²⁺ leakage occurred by enhancing the binding affinity of calmodulin (CaM) to RyR2.

METHODS AND RESULTS

A left anterior descending coronary artery ligation MI model was developed in mice. Wild-type (WT) were divided into four groups: sham-operated mice (WT-Sham), sham-operated mice treated with dantrolene (WT-Sham-DAN), MI mice (WT-MI), and MI mice treated with dantrolene (WT-MI-DAN). Homozygous V3599K RyR2 knock-in (KI) mice were divided into two groups: sham-operated mice (KI-Sham) and MI mice (KI-MI). The mice were followed for 12 weeks. Survival was significantly higher in the WT-MI-DAN (73%) and KI-MI groups (70%) than the WT-MI group (40%). Echocardiography, pathological tissue, and epinephrine-induced VT studies showed that LV remodeling and VT were prevented in the WT-MI-DAN and KI-MI groups compared to the WT-MI group. An increase in diastolic Ca²⁺ spark frequency and a decrease in the binding affinity of CaM to the RyR2 were observed at 12 weeks after MI in the WT-MI group, although significant improvements in these values were observed in the WT-MI-DAN and KI-MI groups.

CONCLUSIONS

Pharmacological or genetic stabilization of RyR2 tetrameric structure improves survival after MI by suppressing LV remodeling and proarrhythmia.

Overexpression of the elongation factor MtEF1A1 promotes salt stress tolerance in Arabidopsis thaliana and Medicago truncatula

BACKGROUND

Elongation factor 1 A (EF1A), an essential regulator for protein synthesis, has been reported to participate in abiotic stress responses and environmental adaption in plants. However, the role of EF1A in abiotic stress response was barely studied in Medicago truncatula. Here, we identified elongation factor (EF) genes of M. truncatula and studied the salt stress response function of MtEF1A1 (MTR_6g021805).

RESULTS

A total of 34 EF genes were identified in the M. truncatula genome. Protein domains and motifs of EFs were highly conserved in plants. MtEF1A1 has the highest expression levels in root nodules and roots, followed by the leaves and stems. Transgenic Arabidopsis thaliana overexpressing MtEF1A1 was more resistant to salt stress treatment, with higher germination rate, longer roots, and more lateral roots than wild type plant. In addition, lower levels of H₂O₂ and malondialdehyde (MDA) were also detected in transgenic Arabidopsis. Similarly, MtEF1A1 overexpressing M. truncatula was more resistant to salt stress and had lower levels of reactive oxygen species (ROS) in leaves. Furthermore, the expression levels of abiotic stress-responsive genes (MtRD22A and MtCOR15A) and calcium-binding genes (MtCaM and MtCBL4) were upregulated in MtEF1A1 overexpressing lines of M. truncatula.

CONCLUSION

These results suggested that MtEF1A1 play a positive role in salt stress regulation. MtEF1A1 may realize its function by binding to calmodulin (CaM) or by participating in Ca²⁺-dependent signaling pathway. This study revealed that MtEF1A1 is an important regulator for salt stress response in M. truncatula, and provided potential strategy for salt-tolerant plant breeding.

Development of indolealkylamine derivatives as potential multi-target agents for COVID-19 treatment

COVID-19 is a complex disease with short-term and long-term respiratory, inflammatory and neurological symptoms that are triggered by the infection with SARS-CoV-2. As many drugs targeting single targets showed only limited effectiveness against COVID-19, here, we aimed to explore a multi-target strategy. We synthesized a focused compound library based on C2-substituted indolealkylamines (tryptamines and 5-hydroxytryptamines) with activity for three potential COVID-19-related proteins, namely melatonin receptors, calmodulin and human angiotensin converting enzyme 2 (hACE2). Two molecules from the library, 5e and h, exhibit affinities in the high nanomolar range for melatonin receptors, inhibit the calmodulin-dependent calmodulin kinase II activity and the interaction of the SARS-CoV-2 Spike protein with hACE2 at micromolar concentrations. Both compounds inhibit SARS-CoV-2 entry into host cells and 5h decreases SARS-CoV-2 replication and M^Pro enzyme activity in addition. In conclusion, we provide a proof-of-concept for the successful design of multi-target compounds based on the tryptamine scaffold. Optimization of these preliminary hit compounds could potentially provide drug candidates to treat COVID-19 and other coronavirus diseases.

Nano-calcium alleviates the cracking of nectarine fruit and improves fruit quality

To explore the use of L-aspartic acid nano-calcium (nano-Ca) to reduce nectarine fruit-cracking, we sprayed the crack-susceptible nectarine cultivar 'Huaguang' [Prunus persica (L.) Batsch var. nectarina (Ait.) Maxim.] with nano-Ca. The results showed that nano-Ca could reduce the fruit-cracking percentage of nectarine by more than 20%. Nano-Ca was effective because it increased the calcium pectinate content of the peel, reduced the activity of cell-wall metabolic enzymes, and changed the peel structure and enhanced its toughness. We also found that nano-Ca enhanced calmodulin activity in leaves, upregulated key genes of sucrose synthesis in leaves and sucrose transport in stem phloem, and significantly increased the soluble sugar content in the fruit by more than 2%. In addition, Nano-Ca also enhanced calmodulin activity in peel and up-regulated key genes related to anthocyanin-synthesis, promoting anthocyanin accumulation in the peel. The result will lay a theoretical foundation for the physiological and molecular mechanisms of nectarine-cracking and its prevention.

CaCl(2) treatment effectively delays postharvest senescence of passion fruit

This study aimed to systematically investigate the changes in peel color, physicochemical characteristics, textural properties, and peel ultrastructure between CaCl₂-treated and water-soaked passion fruit under short-term storage at room temperature (20 °C) for eight days. The fruit peel was further analyzed and compared for the differences in calmodulin (CaM) gene expression between the two groups. The data were analyzed using principal component analysis. The results confirmed that CaCl₂ treatment effectively maintained the appearance and color of passion fruit, inhibited peel browning, and improved fruit quality. The treatment had an effect on maintaining the physiological properties of passion fruit parenchyma, effectively delayed the passion fruit senescence, and kept the structural integrity of the fruit peel. The relative expression of PeCaM gene in the CaCl₂-treated fruit peels was higher than that of the control peels. The Ca²⁺ stimulated the relative expression of the PeCaM gene, which delayed the senescence of passion fruit.

NaV1.6 dysregulation within myocardial T-tubules by D96V calmodulin enhances proarrhythmic sodium and calcium mishandling

Calmodulin (CaM) plays critical roles in cardiomyocytes, regulating Na+ (NaV) and L-type Ca2+ channels (LTCC). LTCC dysregulation by mutant CaMs has been implicated in action potential duration (APD) prolongation and arrhythmogenic long QT (LQT) syndrome. Intriguingly, D96V-CaM prolongs APD more than other LQT-associated CaMs despite inducing comparable levels of LTCC dysfunction, suggesting dysregulation of other depolarizing channels. Here, we provide evidence implicating NaV dysregulation within transverse (T)-tubules in D96V-CaM-associated arrhythmias. D96V-CaM induces pro-arrhythmic late Na+ current (INa) by impairing inactivation of NaV1.6, but not the predominant cardiac NaV isoform, NaV1.5. We investigated arrhythmia mechanisms using mice with cardiac-specific expression of D96V-CaM (cD96V). Super-resolution microscopy revealed close proximity of NaV1.6 and RyR2 within T-tubules. NaV1.6 density within these regions increased in cD96V relative to WT. Consistent with NaV1.6 dysregulation by D96V-CaM in these regions, we observed increased late NaV activity in T-tubules. The resulting late INa promoted aberrant Ca2+ release and prolonged APD in myocytes, leading to LQT and ventricular tachycardia (VT) in vivo. Cardiac-specific NaV1.6 knockout protected cD96V mice from increased T-tubular late NaV activity, and its arrhythmogenic consequences. In summary, we demonstrate that D96V-CaM promotes arrhythmias by dysregulating LTCC and NaV1.6 within T-tubules and thereby, facilitating aberrant Ca2+ release.

Stabilizing cardiac ryanodine receptor with dantrolene treatment prevents left ventricular remodeling in pressure-overloaded heart failure mice

Dantrolene (DAN) directly binds to cardiac ryanodine receptor 2 (RyR2) through Leu⁶⁰¹-Cys⁶²⁰ in the N-terminal domain and subsequently inhibits diastolic Ca²⁺ leakage through RyR2. We previously reported that therapy using RyR2 V3599K mutation, which inhibits diastolic Ca²⁺ leakage by enhancing calmodulin (CaM) binding ability to RyR2, prevents left ventricular (LV) remodeling in transverse aortic constriction (TAC) heart failure. Here, we examined whether chronic administration of DAN prevents LV remodeling in TAC heart failure via the same mechanism as genetic therapy. A pressure-overloaded hypertrophy mouse model was developed using TAC. Wild-type (WT) mice were divided into three groups: sham-operated mice (Sham group), TAC mice (TAC group), and TAC mice treated with DAN (TAC-DAN group, 20 mg/kg/day, i.p.). They were then followed up for 8 weeks. The survival rate was higher in the TAC-DAN group (83%) than in the TAC group (49%), and serial echocardiography studies and pathological tissue analysis showed that LV remodeling was significantly prevented in the TAC-DAN group compared to the TAC group. An increase in the diastolic Ca²⁺ spark frequency and a decrease in the binding affinity of CaM to RyR2 were observed at 8 weeks in the TAC group but not in the TAC-DAN group. Stabilization of RyR2 with DAN prevented LV remodeling and improved survival after TAC by enhancing CaM binding to RyR2 and inhibiting RyR2-mediated diastolic Ca²⁺ leakage.

Regulation of Presynaptic Calcium Channels

Voltage-gated calcium channels (VGCCs), especially Cav2.1 and Cav2.2, are the major mediators of Ca2+ influx at the presynaptic membrane in response to neuron excitation, thereby exerting a predominant control on synaptic transmission. To guarantee the timely and precise release of neurotransmitters at synapses, the activity of presynaptic VGCCs is tightly regulated by a variety of factors, including auxiliary subunits, membrane potential, G protein-coupled receptors (GPCRs), calmodulin (CaM), Ca2+-binding proteins (CaBP), protein kinases, various interacting proteins, alternative splicing events, and genetic variations.

Hydrophobic interactions within the C terminus pole helices tunnel regulate calcium-dependent inactivation of TRPC3 in a calmodulin-dependent manner

Recent structural studies have shown that the carboxyl-terminus of many TRP channels, including TRPC3, are folded into a horizontal rib helix that is connected to the vertical pole helix, which play roles in inter-structural interactions and multimerization. In a previous work we identified I807 located in the pole helix with a role in regulation of TRPC3 by STIM1 (Lee et al., 2014, Liu et al., 2022). To further determine the role of the pole helix in TRPC3 function, here we identified key hydrophobic residues in the pole helix that form tight tunnel-like structure and used mutations to probe their role in TRPC3 regulation by Ca2+ and Calmodulin. Our findings suggest that the hydrophobic starch formed by the I807-L818 residues has several roles, it modulates gating of TRPC3 by Ca2+, affects channel selectivity and the channel Ca2+ permeability. Mutations of I807, I811, L814 and L818 all attenuated the Ca2+-dependent inactivation (CDI) of TRPC3, with I807 having the most prominent effect. The extent of modulation of the CDI depended on the degree of hydrophobicity of I807. Moreover, the TRPC3(I807S) mutant showed altered channel monovalent ion selectivity and increased Ca2+ permeability, without affecting the channel permeability to Mg2+ and Ba2+ and without changing the pore diameter. The CDI of TRPC3 was reduced by an inactive calmodulin mutant and by a pharmacological inhibitor of calmodulin, which was eliminated by the I807S mutation. Notably, deletion of STIM1 caused similar alteration of TRPC3 properties. Taken together, these findings reveal a role of the pole helix in CDI, in addition to its potential role in channel multimerization that required gating of TRPC3 by STIM1. Since all TRPC and most TRP channels have pole helix structures, our findings raise the possibility that the pole helix may have similar roles in all the TRP family.

Identification of Saccharum CaM gene family and function characterization of ScCaM1 during cold and oxidant exposure in Pichia pastoris

BACKGROUND

Calmodulin (CaM) plays an essential role in binding calcium ions and mediating the interpretation of Ca²⁺ signals in plants under various stresses. However, the evolutionary relationship of CaM family proteins in Saccharum has not been elucidated.

OBJECTIVE

To deduce and explore the evolution and function of Saccharum CaM family.

METHODS

A total of 104 typical CaMs were obtained from Saccharum spontaneum and other 18 plant species. The molecular characteristics and evolution of those CaM proteins were analyzed. A typical CaM gene, ScCaM1, was subsequently cloned from sugarcane (Saccharum spp. hybrid). Its expression patterns in different tissues and under various abiotic stresses were assessed by quantitative real-time PCR. Then the green fluorescent protein was used to determine the subcellular localization of ScCaM1. Finally, the function of ScCaM1 was evaluated via heterologous yeast expression systems.

RESULTS

Three typical CaM members (SsCaM1, SsCaM2, and SsCaM3) were identified from the S. spontaneum genome database. CaMs were originated from the two last common ancestors before the origin of angiosperms. The number of CaM family members did not correlate to the genome size but correlated with allopolyploidization events. The ScCaM1 was more highly expressed in buds and roots than in other tissues. The expression patterns of ScCaM1 suggested that it was involved in responses to various abiotic stresses in sugarcane via different hormonal signaling pathways. Noteworthily, its expression levels appeared relatively stable during the cold exposure in the cold-tolerant variety but significantly suppressed in the cold-susceptible variety. Moreover, the recombinant yeast (Pichia pastoris) overexpressing ScCaM1 grew better than the wild-type yeast strain under cold and oxidative stresses. It was revealed that the ScCaM1 played a positive role in reactive oxygen species scavenging and conferred enhanced cold and oxidative stress tolerance to cells.

CONCLUSION

This study provided comprehensive information on the CaM gene family in Saccharum and would facilitate further investigation of their functional characterization.

Genome-wide identification and expression analysis of calmodulin and calmodulin-like genes in wheat (Triticum aestivum L.)

Calmodulin (CaM) and calmodulin-like (CML) genes are widely involved in plant growth and development and mediating plant stress tolerance. However, the whole genome scale studies about CaM and CML gene families have not been done in wheat, and the possible functions of most wheat CaM/CML gene members are still unknown. In this study, a total of 18 TaCaM and 230 TaCML gene members were identified in wheat genome. Among these genes, 28 TaCaM/CML gene members have 74 duplicated copies, while 21 genes have 48 transcript variants, resulting in 321 putative TaCaM/CML transcripts totally. Phylogenetic tree analysis showed that they can be classified into 7 subfamilies. Similar gene structures and protein domains can be found in members of the same gene cluster. The TaCaM/CML genes were spread among all 21 chromosomes with unbalanced distributions, while most of the gene clusters contained 3 homoeologous genes located in the same homoeologous chromosome group. Synteny analysis showed that most of TaCaM/CMLs gene members can be found with 1-4 paralogous genes in T. turgidum and Ae. Tauschii. High numbers of cis-acting elements related to plant hormones and stress responses can be observed in the promoters of TaCaM/CMLs. The spatiotemporal expression patterns showed that most of the TaCaM/TaCML genes can be detected in at least one tissue. The expression levels of TaCML17, 21, 30, 50, 59 and 75 in the root or shoot can be up-regulated by abiotic stresses, suggesting that TaCML17, 21, 30, 50, 59 and 75 may be related with responses to abiotic stresses in wheat. The spatiotemporal expression patterns of TaCaM/CML genes indicated they may be involved widely in wheat growth and development. Our results provide important clues for exploring functions of TaCaMs/CMLs in growth and development as well as responses to abiotic stresses in wheat in the future.

Structure and function of the N-terminal extension of the formin INF2

In INF2—a formin linked to inherited renal and neurological disease in humans—the DID is preceded by a short N-terminal extension of unknown structure and function. INF2 activation is achieved by Ca²⁺-dependent association of calmodulin (CaM). Here, we show that the N-terminal extension of INF2 is organized into two α-helices, the first of which is necessary to maintain the perinuclear F-actin ring and normal cytosolic F-actin content. Biochemical assays indicated that this helix interacts directly with CaM and contains the sole CaM-binding site (CaMBS) detected in INF2. The residues W11, L14 and L18 of INF2, arranged as a 1-4-8 motif, were identified as the most important residues for the binding, W11 being the most critical of the three. This motif is conserved in vertebrate INF2 and in the human population. NMR and biochemical analyses revealed that CaM interacts directly through its C-terminal lobe with the INF2 CaMBS. Unlike control cells, INF2 KO cells lacked the perinuclear F-actin ring, had little cytosolic F-actin content, did not respond to increased Ca²⁺ concentrations by making more F-actin, and maintained the transcriptional cofactor MRTF predominantly in the cytoplasm. Whereas expression of intact INF2 restored all these defects, INF2 with inactivated CaMBS did not. Our study reveals the structure of the N-terminal extension, its interaction with Ca²⁺/CaM, and its function in INF2 activation.

Chemical shift assignments of the C-terminal domain of CaBP1 bound to the IQ-motif of voltage-gated Ca2+ channel (CaV1.2)

The neuronal L-type voltage-gated Ca²⁺ channel (Ca_V1.2) interacts with Ca²⁺ binding protein 1 (CaBP1), that promotes Ca²⁺-induced channel activity. The binding of CaBP1 to the IQ-motif in Ca_V1.2 (residues 1644-1665) blocks the binding of calmodulin and prevents Ca²⁺-dependent inactivation of Ca_V1.2. This Ca²⁺-induced binding of CaBP1 to Ca_V1.2 is important for modulating neuronal synaptic plasticity, which may serve a role in learning and memory. Here we report NMR assignments of the C-terminal domain of CaBP1 (residues 99-167, called CaBP1C) that contains two Ca²⁺ bound at the third and fourth EF-hands (EF3 and EF4) and is bound to the Ca_V1.2 IQ-motif from Ca_V1.2 (BMRB accession no. 51518).

Time-resolved solid state NMR of biomolecular processes with millisecond time resolution

We review recent efforts to develop and apply an experimental approach to the structural characterization of transient intermediate states in biomolecular processes that involve large changes in molecular conformation or assembly state. This approach depends on solid state nuclear magnetic resonance (ssNMR) measurements that are performed at very low temperatures, typically 25-30 K, with signal enhancements from dynamic nuclear polarization (DNP). This approach also involves novel technology for initiating the process of interest, either by rapid mixing of two solutions or by a rapid inverse temperature jump, and for rapid freezing to trap intermediate states. Initiation by rapid mixing or an inverse temperature jump can be accomplished in approximately-one millisecond. Freezing can be accomplished in approximately 100 microseconds. Thus, millisecond time resolution can be achieved. Recent applications to the process by which the biologically essential calcium sensor protein calmodulin forms a complex with one of its target proteins and the process by which the bee venom peptide melittin converts from an unstructured monomeric state to a helical, tetrameric state after a rapid change in pH or temperature are described briefly. Future applications of millisecond time-resolved ssNMR are also discussed briefly.

Dynamics and structural changes of calmodulin upon interaction with the antagonist calmidazolium

Background

Calmodulin (CaM) is an evolutionarily conserved eukaryotic multifunctional protein that functions as the major sensor of intracellular calcium signaling. Its calcium-modulated function regulates the activity of numerous effector proteins involved in a variety of physiological processes in diverse organs, from proliferation and apoptosis, to memory and immune responses. Due to the pleiotropic roles of CaM in normal and pathological cell functions, CaM antagonists are needed for fundamental studies as well as for potential therapeutic applications. Calmidazolium (CDZ) is a potent small molecule antagonist of CaM and one the most widely used inhibitors of CaM in cell biology. Yet, CDZ, as all other CaM antagonists described thus far, also affects additional cellular targets and its lack of selectivity hinders its application for dissecting calcium/CaM signaling. A better understanding of CaM:CDZ interaction is key to design analogs with improved selectivity. Here, we report a molecular characterization of CaM:CDZ complexes using an integrative structural biology approach combining SEC-SAXS, X-ray crystallography, HDX-MS, and NMR.

Results

We provide evidence that binding of a single molecule of CDZ induces an open-to-closed conformational reorientation of the two domains of CaM and results in a strong stabilization of its structural elements associated with a reduction of protein dynamics over a large time range. These CDZ-triggered CaM changes mimic those induced by CaM-binding peptides derived from physiological protein targets, despite their distinct chemical natures. CaM residues in close contact with CDZ and involved in the stabilization of the CaM:CDZ complex have been identified.

Conclusion

Our results provide molecular insights into CDZ-induced dynamics and structural changes of CaM leading to its inhibition and open the way to the rational design of more selective CaM antagonists.

Graphical abstract

Calmidazolium is a potent and widely used inhibitor of calmodulin, a major mediator of calcium-signaling in eukaryotic cells. Structural characterization of calmidazolium-binding to calmodulin reveals that it triggers open-to-closed conformational changes similar to those induced by calmodulin-binding peptides derived from enzyme targets. These results provide molecular insights into CDZ-induced dynamics and structural changes of CaM leading to its inhibition and open the way to the rational design of more selective CaM antagonists.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01381-5.

Neurogranin inhibits calcineurin in murine soleus muscle: Effects of heterozygous knockdown on muscle adaptations to tenotomy and fatigue resistance

Neurogranin (Ng) is a calmodulin (CaM) binding protein that negatively regulates calcineurin - a Ca²⁺/CaM-dependent phosphatase that can mitigate the slow-to-fast fibre type shift observed with muscle unloading. Here, we questioned whether heterozygous deletion of Ng (Ng^+/-) would enhance calcineurin activity, thereby minimizing the slow-to-fast fibre type shift caused by muscle unloading. As expected, soleus muscles from young adult (3-4 months old) Ng^± mice had lowered Ng content and enhanced calcineurin activity when compared to soleus muscles obtained from male age-matched wild-type (WT) mice. Two weeks after tenotomy surgery, where the soleus and gastrocnemius tendons were severed, soleus total fibre count were found to be similarly reduced across both genotypes. However, significant reductions in myofibre cross-sectional area were only found in WT mice and not Ng^± mice. Furthermore, while soleus muscles from both WT and Ng^± mice exhibited a slow-to-fast fibre type shift with tenotomy, soleus muscles from Ng^± mice, in both sham and tenotomized conditions, had a greater proportion of oxidative fibres (type I and IIA) compared with that of WT mice. Corresponding well with this, we found that soleus muscles from Ng^± mice were more fatigue resistant compared with those obtained from their WT counterparts. Collectively, these findings show that heterozygous Ng deletion increases calcineurin activation, preserves myofibre size in response to unloading, and promotes the oxidative fibre type to ultimately enhance fatigue resistance. This study demonstrates the role of Ng in regulating calcineurin in vivo and its influence on skeletal muscle form and function.

Calcium/calmodulin-dependent protein kinase kinase 2 mediates pleiotropic effects of epidermal growth factor in cancer cells

AIMS

Engagement of epidermal growth factor (EGF) with its receptor (EGFR) produces a broad range of cancer phenotypes. The overriding aim of this study was to understand EGFR signaling and its regulation by the Ca²⁺/calmodulin (CaM) dependent protein kinase kinase 2 (CaMKK2) in cancer cells.

RESULTS

In ovarian cancer cells and other cancer cell types, EGF-induced activation of oncogenic Akt is mediated by both the canonical PI3K-PDK1 pathway and by CaMKK2. Akt activation induced by EGF occurs by both calcium-dependent and calcium-independent mechanisms. In contrast to the canonical pathway, CaMKK2 neither binds to, nor is regulated by phosphoinositides but is activated by Ca²⁺/CaM. Akt activation at its primary activation site, T308 occurs by direct phosphorylation by CaMKK2, but activation at its secondary site (S473), is through an indirect mechanism requiring mTORC2. In cells in which another CaMKK2 target, 5'AMP-dependent protein kinase (AMPK) was deleted, Akt activation and calcium-dependency of activation were still observed. CaMKK2 accumulates in the nucleus in response to EGF and regulates transcription of phosphofructokinase platelet (PFKP) a glycolytic regulator. CaMKK2 is required for optimal PFK activity. CaMKK2 regulates transcription of plasminogen activator, urokinase (PLAU) a metastasis regulator. The EGFR inhibitor gefitinib synergizes with CaMKK2 inhibition in the regulation of cell survival and increases the dose-reduction index. CRISPR/Cas9 knockout of CaMKK2 leads to compensatory PTEN downregulation and upregulation of Akt activation.

CONCLUSIONS

CaMKK2-mediation of EGFR action may enable cancer cells to use intracellular calcium elevation as a signal for growth and survival.

Engineering tropane alkaloid production and glyphosate resistance by overexpressing AbCaM1 and G2-EPSPS in Atropa belladonna

Atropa belladonna is an important industrial crop for producing anticholinergic tropane alkaloids (TAs). Using glyphosate as selection pressure, transgenic homozygous plants of A. belladonna are generated, in which a novel calmodulin gene (AbCaM1) and a reported EPSPS gene (G2-EPSPS) are co-overexpressed. AbCaM1 is highly expressed in secondary roots of A. belladonna and has calcium-binding activity. Three transgenic homozygous lines were generated and their glyphosate tolerance and TAs' production were evaluated in the field. Transgenic homozygous lines produced TAs at much higher levels than wild-type plants. In the leaves of T2GC02, T2GC05, and T2GC06, the hyoscyamine content was 8.95-, 10.61-, and 9.96 mg/g DW, the scopolamine content was 1.34-, 1.50- and 0.86 mg/g DW, respectively. Wild-type plants of A. belladonna produced hyoscyamine and scopolamine respectively at the levels of 2.45 mg/g DW and 0.30 mg/g DW in leaves. Gene expression analysis indicated that AbCaM1 significantly up-regulated seven key TA biosynthesis genes. Transgenic homozygous lines could tolerate a commercial recommended dose of glyphosate in the field. In summary, new varieties of A. belladonna not only produce pharmaceutical TAs at high levels but tolerate glyphosate, facilitating industrial production of TAs and weed management at a much lower cost.

Highly conserved protein Rv1211 in Mycobacterium tuberculosis is a natively unfolded protein that binds to a calmodulin antagonist, trifluoperazine

Rv1211 is a conserved hypothetical protein in Mycobacterium tuberculosis and is required for the growth and pathogenesis of the bacteria. The protein has been suggested as a calmodulin-like calcium-binding protein with an EF-hand motif and as a target of trifluoperazine, a calmodulin antagonist in eukaryotes that inhibits mycobacterial growth. Here, we expressed the recombinant protein of Rv1211 and performed structural and biochemical studies of Rv1211 and its interaction with Ca²⁺ or trifluoperazine. Surprisingly, Rv1211 exhibited an elution property typical of a natively unfolded protein. Subsequent circular dichroism experiments with temperature elevation and trifluoroethanol treatment showed that Rv1211 has unfolded structure. Additional NMR experiment confirmed the unfolded state of the protein and further showed that it does not bind to Ca²⁺. Still, Rv1211 did bind to trifluoperazine, as evidenced by the two-dimensional NMR spectra of ¹⁵N-labeled Rv1211. However, there were no peak shifts upon binding, showing that Rv1211 retained its unfolded state even after the trifluoperazine binding. The residues involved in the binding were clustered in the C-terminal region, as identified by the sequence assignment. Isothermal titration calorimetry showed that the K_d of trifluoperazine-Rv1211 binding is 41 μM and that the stoichiometry is 1 : 2 (Rv1211: trifluoperazine). Our results argue against the suggestion of Rv1211 as a Ca²⁺-binding calmodulin-like protein, and show that Rv1211 is a natively unfolded protein that binds to trifluoperazine. In addition, our results suggest the evidence of the "Fuzziness" in the Rv1211-trifluoperazine interaction that differs from the conventional binding-induced folding of natively unfolded proteins.

Ca2+ participates in the regulation of microalgae triacylglycerol metabolism under heat stress

Microalgae are the largest CO₂ fixer and O₂ producer on the earth and occupy an increasingly important position in human life and production. Various environmental factors have a significant impact on the growth and metabolism of microalgae. As global warming intensifies, heat stress has become a crucial factor affecting the microalgae industry. However, till now, it has not been clear how microalgae sensed the temperature stress, transmitted stress signals and adjusted in intracellular metabolic pathways. In this study, the growth of microalgae Auxenochlorella protothecoides UTEX2341 was inhibited at 32 °C, but the single cell dry weight increased. The cell component analyses showed that both the carbohydrate and total protein content decreased significantly, while the lipid content increased by 158%. Meanwhile, the intracellular Ca²⁺ concentration increased continuously, with a maximum increase of 1.65 times. According to the transcriptome analyses, the up-regulation of Ca²⁺ influx channel protein mid1-complementing activity 1 (MCA1) gene and the down-regulation of efflux channel protein cation exchanger 1(CAX) and autoinhibited Ca²⁺-ATPase 1 (ACA1) genes in cytoplasmic membrane jointly facilitated the increase of Ca²⁺ in the cytoplasm. Coexpression network analysis indicated that the fluctuation of Ca²⁺ in the cytoplasm could activate the expression of transcription factors MYB3 and AP2-4 through calmodulin (CAM) and calcium-dependent protein kinase (CDPK), and then regulate glycerol-3-phosphate acyltransferases (GPAT) at the beginning of TAG synthesis and diacylglycerol acyltransferase (DGAT)/phospholipid: diacylglycerol acyltransferase (PDAT) in the last step of TAG synthesis. Furthermore, the addition of Ca²⁺ specific chelator BAPTA-AM inhibited the expression of GPAT, which was consistent with the decrease in microalgae lipid content. The results proved that Ca²⁺ participated in the regulation of microalgae TAG synthesis under heat stress, which provided a new view for the understanding of the microalgae lipid accumulation mechanism.