Regulatory functions of calmodulin

Investigation of the effectiveness of intermittent electromagnetic field stimulation for early internal cartilaginous ossification in prechondrocytic ATDC5 cells

Pulsed electromagnetic field (PEMF) stimulation has been widely applied clinically to promote bone healing; however, its detailed mechanism of action, particularly in endochondral ossification, remains elusive, and long-term stimulation is required for its satisfactory effect. The aim of this study was to investigate the involvement of the mammalian target of rapamycin (mTOR) pathway in chondrocyte differentiation and proliferation using a mouse prechondroblast cell line (ATDC5), and establish an efficient PEMF stimulation strategy for endochondral ossification. The changes in cell differentiation (gene expression levels of aggrecan, type II collagen, and type X collagen) and proliferation (cellular uptake of bromodeoxyuridine [BrdU]) in ATDC5 cells in the presence or absence of rapamycin, an mTOR inhibitor, was measured. The effects of continuous and intermittent PEMF stimulation on changes in cell differentiation and proliferation were compared. Rapamycin significantly suppressed the induction of cell differentiation markers and the cell proliferation activity. Furthermore, only intermittent PEMF stimulation continuously activated the mTOR pathway in ATDC5 cells, significantly promoting cell proliferation. These results demonstrate the involvement of the mTOR pathway in chondrocyte differentiation and proliferation and suggest that intermittent PEMF stimulation could be effective as a stimulus for endochondral ossification during fracture healing process, thereby reducing stimulation time.

Identifying Key Binding Interactions Between the Cardiac L-Type Calcium Channel and Calmodulin Using Molecular Dynamics Simulations

Defects in the binding of the calcium sensing protein calmodulin (CaM) to the L-type calcium channel (CaV1.2) or to the ryanodine receptor type 2 (RyR2) can lead to dangerous cardiac arrhythmias with distinct phenotypes, such as long-QT syndrome (LQTS) and catecholaminergic ventricular tachycardia (CPVT). Certain CaM mutations lead to LQTS while other mutations lead to CPVT, but the mechanisms by which a specific mutation can lead to each disease phenotype are not well-understood. In this study, we use long, 2 μs molecular dynamics simulations and a multitrajectory approach to identify the key binding interactions between the IQ domain of CaV1.2 and CaM. Five key interactions are found between CaV1.2 and CaM in the C-lobe, 1 in the central linker, and 2 in the N-lobe. In addition, while 5 key interactions appear between residues 120-149 in the C-lobe of CaM when it interacts with CaV1.2, only 1 key interaction is found within this region of CaM when it interacts with the RyR2. We show that this difference in the distribution of key interactions correlates with the known distribution of CaM mutations that lead to LQTS or CPVT. This correlation suggests that a disruption of key binding interactions is a plausible mechanism that can lead to these two different disease phenotypes.

Leishmania exploits host cAMP/EPAC/calcineurin signaling to induce an IL-33-mediated anti-inflammatory environment for the establishment of infection

Host anti-inflammatory responses are critical for the progression of visceral leishmaniasis, and the pleiotropic cytokine interleukin (IL)-33 was found to be upregulated in infection. Here, we documented that IL-33 induction is a consequence of elevated cAMP-mediated exchange protein activated by cAMP (EPAC)/calcineurin-dependent signaling and essential for the sustenance of infection. Leishmania donovani-infected macrophages showed upregulation of IL-33 and its neutralization resulted in decreased parasite survival and increased inflammatory responses. Infection-induced cAMP was involved in IL-33 production and of its downstream effectors PKA and EPAC, only the latter was responsible for elevated IL-33 level. EPAC initiated Rap-dependent phospholipase C activation, which triggered the release of intracellular calcium followed by calcium/calmodulin complex formation. Screening of calmodulin-dependent enzymes affirmed involvement of the phosphatase calcineurin in cAMP/EPAC/calcium/calmodulin signaling-induced IL-33 production and parasite survival. Activated calcineurin ensured nuclear localization of the transcription factors, nuclear factor of activated T cell 1 and hypoxia-inducible factor 1 alpha required for IL-33 transcription, and we further confirmed this by chromatin immunoprecipitation assay. Administering specific inhibitors of nuclear factor of activated T cell 1 and hypoxia-inducible factor 1 alpha in BALB/c mouse model of visceral leishmaniasis decreased liver and spleen parasite burden along with reduction in IL-33 level. Splenocyte supernatants of inhibitor-treated infected mice further documented an increase in tumor necrosis factor alpha and IL-12 level with simultaneous decrease of IL-10, thereby indicating an overall disease-escalating effect of IL-33. Thus, this study demonstrates that cAMP/EPAC/calcineurin signaling is crucial for the activation of IL-33 and in effect creates anti-inflammatory responses, essential for infection.

Chronic hyperactivation of midbrain dopamine neurons causes preferential dopamine neuron degeneration

Parkinson's disease (PD) is characterized by the death of substantia nigra (SNc) dopamine (DA) neurons, but the pathophysiological mechanisms that precede and drive their death remain unknown. The activity of DA neurons is likely altered in PD, but we understand little about if or how chronic changes in activity may contribute to degeneration. To address this question, we developed a chemogenetic (DREADD) mouse model to chronically increase DA neuron activity, and confirmed this increase using ex vivo electrophysiology. Chronic hyperactivation of DA neurons resulted in prolonged increases in locomotor activity during the light cycle and decreases during the dark cycle, consistent with chronic changes in DA release and circadian disturbances. We also observed early, preferential degeneration of SNc projections, recapitulating the PD hallmarks of selective vulnerability of SNc axons and the comparative resilience of ventral tegmental area axons. This was followed by eventual loss of midbrain DA neurons. Continuous DREADD activation resulted in a sustained increase in baseline calcium levels, supporting an important role for increased calcium in the neurodegeneration process. Finally, spatial transcriptomics from DREADD mice examining midbrain DA neurons and striatal targets, and cross-validation with human patient samples, provided insights into potential mechanisms of hyperactivity-induced toxicity and PD. Our results thus reveal the preferential vulnerability of SNc DA neurons to increased neural activity, and support a potential role for increased neural activity in driving degeneration in PD.

Calcium Signalling in Heart and Vessels: Role of Calmodulin and Downstream Calmodulin-Dependent Protein Kinases

Cardiovascular disease is the major cause of death worldwide. The success of medication and other preventive measures introduced in the last century have not yet halted the epidemic of cardiovascular disease. Although the molecular mechanisms of the pathophysiology of the heart and vessels have been extensively studied, the burden of ischemic cardiovascular conditions has risen to become a top cause of morbidity and mortality. Calcium has important functions in the cardiovascular system. Calcium is involved in the mechanism of excitation-contraction coupling that regulates numerous events, ranging from the production of action potentials to the contraction of cardiomyocytes and vascular smooth muscle cells. Both in the heart and vessels, the rise of intracellular calcium is sensed by calmodulin, a protein that regulates and activates downstream kinases involved in regulating calcium signalling. Among them is the calcium calmodulin kinase family, which is involved in the regulation of cardiac functions. In this review, we present the current literature regarding the role of calcium/calmodulin pathways in the heart and vessels with the aim to summarize our mechanistic understanding of this process and to open novel avenues for research.

Fibrillarin RNA methylase is an interacting protein of Cryptosporidium parvum calmodulin-like protein (CpCML)

Cryptosporidium parvum is an obligate protozoan parasite invading epithelial cells of small intestine of human and animals, and causing diarrheal disease. In apicomplexan parasites, calcium signaling can regulate many essential biological processes such as invasion and migration. As the main intracellular receptor for calcium ions, calmodulins control the activities of hundreds of enzymes and proteins. Calmodulin-like protein (CML) is an important member of the calmodulin family and may play a key role in C. parvum, however, the actual situation is still not clear. The present study aimed to identify the parasite interaction partner proteins of C. parvum calmodulin-like protein (CpCML). By constructing the cpcml bait plasmid, 5 potential CpCML - interacting proteins in C. parvum oocyst were screened by yeast-two-hybrid system (Y2H). Bimolecular fluorescence complementation (BiFC) and Co-immunoprecipitation (Co-IP) were performed as subsequent validations. Fibrillarin RNA methylase (FBL) was identified via this screening method as CpCML interacting protein in C. parvum. The identification of this interaction made it possible to get a further understanding of the function of CpCML and its contribution to the pathogenicity of C. parvum.

Potential protein markers in children with Autistic Spectrum Disorder (ASD) revealed by salivary proteomics

The lack of specific pharmacological therapy for Autistic Spectrum Disorder (ASD) and its clinical heterogeneity demand efforts directed toward the identification of biomarkers to aid in diagnosis. Proteomics offers a new perspective for studying the altered proteins associated with autism spectrum disorders (ASD) and we have saliva as an easy-to-collect biological fluid with important biomolecules for investigating biomarkers in various diseases. In this sense, saliva could be used to identify potential biomarkers of ASD. In the current work, saliva samples were collected from children with different degrees of ASD and healthy children and proteomics approaches were applied to generate data on differentially expressed proteins between groups which will serve as a basis for future validation studies as protein markers. Data are available via ProteomeXchange with identifier PXD030065. As results, 132 proteins were present in 80% of the saliva pools of all analyzed groups. Twenty-five proteins were identified as overexpressed in the group of severe and mild/moderate ASD carriers, among which, eight were identified as potential biomarkers for ASD.

Acetylation stabilises calmodulin-regulated calcium signalling

Calmodulin is a conserved calcium signalling protein that regulates a wide range of cellular functions. Amino‐terminal acetylation is a ubiquitous post‐translational modification that affects the majority of human proteins, to stabilise structure, as well as regulate function and proteolytic degradation. Here, we present data on the impact of amino‐terminal acetylation upon structure and calcium signalling function of fission yeast calmodulin. We show that NatA‐dependent acetylation stabilises the helical structure of the Schizosaccharomyces pombe calmodulin, impacting its ability to associate with myosin at endocytic foci. We go on to show that this conserved modification impacts both the calcium‐binding capacity of yeast and human calmodulins. These findings have significant implications for research undertaken into this highly conserved essential protein.

Mechanistic link between CaM-RyR2 interactions and the genesis of cardiac arrhythmia

In this study, we develop a computational model of the interaction between ryanodine receptor type 2 (RyR2) and calmodulin (CaM) to explore the mechanistic link between CaM-RyR2 interactions and cardiac arrhythmia. Our starting point is a biophysically based computational model of CaM binding to a single RyR2 subunit, which reproduces single-channel RyR2 measurements in lipid bilayers. We then integrate this CaM-RyR2 model into a spatially distributed whole-cell model of Ca cycling, which is used to investigate the relationship between CaM and Ca cycling homeostasis. We show that a reduction in CaM concentration leads to a substantial increase in the rate of spontaneous Ca sparks, and this induces a marked reduction in sarcoplasmic reticulum Ca load during steady-state pacing. Also, we show that a reduction in CaM modifies the RyR2 open probability, which makes the cell more prone to Ca wave propagation. These results indicate that aberrant Ca cycling activity during pacing is determined by the interplay between sarcoplasmic reticulum load reduction and the threshold for Ca wave propagation. Based on these results, we show that when CaM is reduced, Ca waves can occur in a cell and induce action potential perturbations that are arrhythmogenic. Thus, this study outlines a novel, to our knowledge, mechanistic link between CaM-RyR2 binding kinetics and the induction of arrhythmias in the heart.

Calcium ion binding to calmodulin: binding free energy calculation using the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method by incorporating implicit polarization

Binding of calcium ion to calcium-binding proteins (CBP) triggers a large number of biological processes in a cell. CBP are known to play important roles in various diseases, such as cancer, alzheimer, and neuronal problems. However, the calculation of the binding affinity of calcium ion to CBP still possesses a significant challenge to the computational investigators. One of the main reasons for this difficulty is the polarization of CBP due to the binding of calcium. In the current work, we have used the implicit polarization method of Leontyev et al. (PCCP, 13.7 (2011): 2613-2626) to calculate the binding free energy of calcium ion binding to calmodulin, an important CBP. We have used the widely used MM-PBSA method to find a good protocol of calculation with implicit polarization. We have also optimized the best value of the calcium radius to match the experimental results. Our results show incorporation of polarization improves the agreement between the calculated and experimental results, although still, some discrepancy remains. On the whole, this work shows implicit polarization when combined with the MM-PBSA method can give results better than calculation without any polarization, and further improvement is necessary to get a quantitative match with experiments.Communicated by Ramaswamy H. Sarma.

The EF-Hand Protein CALML6 Suppresses Antiviral Innate Immunity by Impairing IRF3 Dimerization

The transcription factor IRF3 is phosphorylated in response to viral infection, and it subsequently forms a homodimer and translocates into the nucleus to induce the transcription of genes important for antiviral immunity, such as type I interferons (IFNs). This multistep process is essential for host defense against viral infection, but its regulation remains elusive. Here, we report that the EF-hand protein calmodulin-like 6 (CALML6) directly bound to the phosphorylated serine-rich (SR) region of IRF3 and impaired its dimerization and nuclear translocation. Enforced CALML6 expression suppressed viral infection-induced production of IFN-β and expression of IFN-stimulated genes (ISGs), whereas CALML6 deficiency had the opposite effect. In addition, impaired IFN-β and ISG expression in bone-marrow-derived macrophages and tissues of CALML6 transgenic mice promoted viral replication. These findings identify a phosphorylation-dependent negative feedback loop that maintains the homeostasis of antiviral innate immunity.

Calmodulin Mutations Associated with Heart Arrhythmia: A Status Report

Calmodulin (CaM) is a ubiquitous intracellular Ca²⁺ sensing protein that modifies gating of numerous ion channels. CaM has an extraordinarily high level of evolutionary conservation, which led to the fundamental assumption that mutation would be lethal. However, in 2012, complete exome sequencing of infants suffering from recurrent cardiac arrest revealed de novo mutations in the three human CALM genes. The correlation between mutations and pathophysiology suggests defects in CaM-dependent ion channel functions. Here, we review the current state of the field for all reported CaM mutations associated with cardiac arrhythmias, including knowledge of their biochemical and structural characteristics, and progress towards understanding how these mutations affect cardiac ion channel function.

Gene and Biochemical Pathway Evaluation of Burns Injury via Protein-Protein Interaction Network Analysis

Background:

Severe burns injury can affect several vital systems in the body and can cause inflammation in organs such as the heart, liver, and kidney. Many inflammatory mediators and regulatory hormones related to burn injuries are recognized. In this study, the genes related to burn injury interacted via network analysis, and the central nodes were enriched through gene ontology (GO).

Materials and Methods:

Disease query of STRING database was used for data gathering, and the network was constructed using Cytoscape software version 3.6.0. After gene screening, the central nodes were enriched via GO analysis by ClueGO. The highlighted genes and pathways were clustered and analyzed in detail.

Results:

Among 1067 genes, 35 critical genes that are involved in the 14 highlighted biochemical pathways were recognized. Interpretation of the finding indicates that a number of central genes can be considered as potential biomarkers related to burn injury.

Conclusion:

Can we revise to "Burn injuries have features that are common to several diseases and increases their risk.

Atrial Infarction-Induced Spontaneous Focal Discharges and Atrial Fibrillation in Sheep: Role of Dantrolene-Sensitive Aberrant Ryanodine Receptor Calcium Release

BACKGROUND

The mechanisms underlying spontaneous atrial fibrillation (AF) associated with atrial ischemia/infarction are incompletely elucidated. Here, we investigate the mechanisms underlying spontaneous AF in an ovine model of left atrial myocardial infarction (LAMI).

METHODS AND RESULTS

LAMI was created by ligating the atrial branch of the left anterior descending coronary artery. ECG loop recorders were implanted to monitor AF episodes. In 7 sheep, dantrolene-a ryanodine receptor blocker-was administered in vivo during the 8-day observation period (LAMI-D, 2.5 mg/kg, IV, BID). LAMI animals experienced numerous spontaneous AF episodes during the 8-day monitoring period that were suppressed by dantrolene (LAMI, 26.1±5.1; sham, 4.3±1.1; LAMI-D, 2.8±0.8; mean±SEM episodes per sheep, P<0.01). Optical mapping showed spontaneous focal discharges (SFDs) originating from the ischemic/normal-zone border. SFDs were calcium driven, rate dependent, and enhanced by isoproterenol (0.03 µmol/L, from 210±87 to 3816±1450, SFDs per sheep) but suppressed by dantrolene (to 55.8±32.8, SFDs per sheep, mean±SEM). SFDs initiated AF-maintaining reentrant rotors anchored by marked conduction delays at the ischemic/normal-zone border. NOS1 (NO synthase-1) protein expression decreased in ischemic zone myocytes, whereas NADPH (nicotinamide adenine dinucleotide phosphate, reduced form) oxidase and xanthine oxidase enzyme activities and reactive oxygen species (DCF [6-carboxy-2',7'-dichlorodihydrofluorescein diacetate]-fluorescence) increased. CaM (calmodulin) aberrantly increased [³H]ryanodine binding to cardiac RyR2 (ryanodine receptors) in the ischemic zone. Dantrolene restored the physiological binding of CaM to RyR2.

CONCLUSIONS

Atrial ischemia causes spontaneous AF episodes in sheep, caused by SFDs that initiate reentry. Nitroso-redox imbalance in the ischemic zone is associated with intense reactive oxygen species production and altered RyR2 responses to CaM. Dantrolene administration normalizes the CaM response, prevents LAMI-related SFDs, and AF initiation. These findings provide novel insights into the mechanisms underlying ischemia-related atrial arrhythmias.

Pep5, a Fragment of Cyclin D2, Shows Antiparasitic Effects in Different Stages of the Trypanosoma cruzi Life Cycle and Blocks Parasite Infectivity

Pep5 (WELVVLGKL) is a fragment of cyclin D2 that exhibits a 2-fold increase in the S phase of the HeLa cell cycle. When covalently bound to a cell-penetrating peptide (Pep5-cpp), the nonapeptide induces cell death in several tumor cells, including breast cancer and melanoma cells. Additionally, Pep5-cpp reduces the in vivo tumor volume of rat glioblastoma. Chagas disease, which is caused by the flagellated parasite Trypanosoma cruzi, is a neglected disease that occurs mainly in the Americas, where it is considered an important public health issue. Given that there are only two options for treating the disease, it is exceptionally crucial to search for new molecules with potential pharmacological action against the parasites. In this study, we demonstrate that Pep5-cpp induces cell death in epimastigote, trypomastigote, and amastigote forms of T. cruzi The Pep5-cpp peptide was also able to decrease the percentage of infected cells without causing any detectable toxic effects in mammalian host cells. The infective, i.e., trypomastigote form of T. cruzi pretreated with Pep5-cpp was unable to infect LLC-MK₂ monkey kidney cells. Also, Pep5-binding proteins were identified by mass spectrometry, including calmodulin-ubiquitin-associated protein, which is related to the virulence and parasitemia of T. cruzi Taken together, these data suggest that Pep5 can be used as a novel alternative for the treatment of Chagas disease.

Secondary structures in synthetic polypeptides from N-carboxyanhydrides: design, modulation, association, and material applications

This article highlights the conformation-specific properties and functions of synthetic polypeptides derived from N-carboxyanhydrides.

Divergent Soybean Calmodulins Respond Similarly to Calcium Transients: Insight into Differential Target Regulation

Plants commonly respond to stressors by modulating the expression of a large family of calcium binding proteins including isoforms of the ubiquitous signaling protein calmodulin (CaM). The various plant CaM isoforms are thought to differentially regulate the activity of specific target proteins to modulate cellular stress responses. The mechanism(s) behind differential target activation by the plant CaMs is unknown. In this study, we used steady-state and stopped-flow fluorescence spectroscopy to investigate the strategy by which two soybean CaMs (sCaM1 and sCaM4) have evolved to differentially regulate NAD kinase (NADK), which is activated by sCaM1 but inhibited by sCaM4. Although the isolated proteins have different cation binding properties, in the presence of Mg2+ and the CaM binding domains from proteins that are differentially regulated, the two plant CaMs respond nearly identically to rapid and slow Ca2+ transients. Our data suggest that the plant CaMs have evolved to bind certain targets with comparable affinities, respond similarly to a particular Ca2+ signature, but achieve different structural states, only one of which can activate the enzyme. Understanding the basis for differential enzyme regulation by the plant CaMs is the first step to engineering a vertebrate CaM that will selectively alter the CaM signaling network.

ALG-2 activates the MVB sorting function of ALIX through relieving its intramolecular interaction

The modular adaptor protein ALIX is critically involved in endosomal sorting complexes required for transport (ESCRT)-mediated multivesicular body (MVB) sorting of activated epidermal growth factor receptor (EGFR); however, ALIX contains a default intramolecular interaction that renders ALIX unable to perform this ESCRT function. The ALIX partner protein ALG-2 is a calcium-binding protein that belongs to the calmodulin superfamily. Prompted by a defined biological function of calmodulin, we determined the role of ALG-2 in regulating ALIX involvement in MVB sorting of activated EGFR. Our results show that calcium-dependent ALG-2 interaction with ALIX completely relieves the intramolecular interaction of ALIX and promotes CHMP4-dependent ALIX association with the membrane. EGFR activation induces increased ALG-2 interaction with ALIX, and this increased interaction is responsible for increased ALIX association with the membrane. Functionally, inhibition of ALIX activation by ALG-2 inhibits MVB sorting of activated EGFR as effectively as inhibition of ALIX interaction with CHMP4 does; however, inhibition of ALIX activation by ALG-2 does not affect cytokinetic abscission or equine infectious anemia virus (EIAV) budding. These findings indicate that calcium-dependent ALG-2 interaction with ALIX is specifically responsible for generating functional ALIX that supports MVB sorting of ubiquitinated membrane receptors.

Effects of low seawater pH on the marine polychaete Platynereis dumerilii

An important priority for any organism is to maintain internal cellular homeostasis including acid-base balance. Yet, the molecular level impacts of changing environmental conditions, such as low pH, remain uncharacterised. Herein, we isolate partial Na(+)/H(+)exchangers (NHE), carbonic anhydrase (CA), and calmodulin (CaM) genes from a polychaete, Platynereis dumerilii and investigate their relative expression in acidified seawater conditions. mRNA expression of NHE was significantly down-regulated after 1h and up-regulated after 7days under low pH treatment (pH 7.8), indicating changes in acid-base transport. Furthermore, the localisation of NHE expression was also altered. A trend of down regulation in CA after 1h was also observed, suggesting a shift in the CO2 and HCO3(-) balance. No change in CaM expression was detected after 7days exposure to acidified seawater. This study provides insight into the molecular level changes taking place following exposure to acidified seawater in a non-calcifying, ubiquitous, organism.

Melatonin improves experimental colitis with sleep deprivation

Sleep deprivation (SD) is an epidemic phenomenon in modern countries, and its harmful effects are well known. SD acts as an aggravating factor in inflammatory bowel disease. Melatonin is a sleep-related neurohormone, also known to have antioxidant and anti-inflammatory effects in the gastrointestinal tract; however, the effects of melatonin on colitis have been poorly characterized. Thus, in this study, we assessed the measurable effects of SD on experimental colitis and the protective effects of melatonin. For this purpose, male imprinting control region (ICR) mice (n=24) were used; the mice were divided into 4 experimental groups as follows: the control, colitis, colitis with SD and colitis with SD and melatonin groups. Colitis was induced by the administration of 5% dextran sulfate sodium (DSS) in the drinking water for 6 days. The mice were sleep-deprived for 3 days. Changes in body weight, histological analyses of colon tissues and the expression levels of pro-inflammatory cytokines and genes were evaluated. SD aggravated inflammation and these effects were reversed by melatonin in the mice with colitis. In addition, weight loss in the mice with colitis with SD was significantly reduced by the injection of melatonin. Treatment with melatonin led to high survival rates in the mice, in spite of colitis with SD. The levels of pro-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, IL-17, interferon-γ and tumor necrosis factor-α, in the serum of mice were significantly increased by SD and reduced by melatonin treatment. The melatonin-treated group showed a histological improvement of inflammation. Upon gene analysis, the expression of the inflammatory genes, protein kinase Cζ (PKCζ) and calmodulin 3 (CALM3), was increased by SD, and the levels decreased following treatment with melatonin. The expression levels of the apoptosis-related inducible nitric oxide synthase (iNOS) and wingless-type MMTV integration site family, member 5A (Wnt5a) genes was decreased by SD, but increased following treatment with melatonin. Treatment with melatonin reduced weight loss and prolonged survival in mice with colitis with SD. Melatonin exerted systemic anti-inflammatory effects. Gene analysis revealed a possible mechanism of action of melatonin in inflammation and sleep disturbance. Thus, melatonin may be clinically applicable for patients with inflammatory bowel disease, particulary those suffering from sleep disturbances.

Calcium rapidly down-regulates human renal epithelial sodium channels via a W-7-sensitive mechanism

Increases in intracellular calcium (Ca(2+)) inhibit renal sodium (Na(+)) absorption in cortical collecting ducts, but the precise mechanism is unclear. We, therefore, studied the effects of raising intracellular Ca(2+) (using 10 µmol/L A23187, a Ca(2+) ionophore) on wild-type and Liddle-mutated human epithelial Na(+) channels (hENaC) expressed in Xenopus oocytes, using the dual-electrode voltage clamp technique. A23187 decreased amiloride-sensitive Na(+) current by 55% in oocytes expressing wild-type hENaC, an effect prevented by co-exposure to 50 μmol/L W-7 (to inhibit the Ca(2+)/calmodulin complex). By contrast, co-exposure to 50 μmol/L calphostin (to inhibit protein kinase C) or 5 μmol/L KN-62 (to inhibit Ca(2+)/calmodulin-dependent protein kinase II) had no effect on the decrease in amiloride-sensitive Na(+) current elicited by A23187 alone. Whereas A23187 reduced amiloride-sensitive Na(+) current in oocytes expressing wild-type hENaC, it had no similar effect in those expressing Liddle-mutated hENaCs, suggesting that the activity of individual Na(+) channels in situ was unchanged by the rise in intracellular Ca(2+). These data suggest that the A23187-induced rise in intracellular Ca(2+) inhibited wild-type hENaC through a W-7-sensitive mechanism, which likely reflected enhanced removal of Na(+) channels from the cell membrane by endocytosis. We, therefore, propose that Na(+) absorption in cortical collecting duct cells is inhibited by Ca(2+), possibly when complexed with calmodulin.

The calmodulin-like protein CML43 functions as a salicylic-acid-inducible root-specific Ca(2+) sensor in Arabidopsis

Many signalling pathways in plants are regulated by the second messenger calcium (Ca(2+)). In the standard model, Ca(2+)-sensor proteins, such as CaM (calmodulin), detect Ca(2+) signals and subsequently regulate downstream targets to advance the signal transduction cascade. In addition to CaM, plants possess many CMLs (CaM-like proteins) that are predicted to function as Ca(2+) sensors, but which remain largely uncharacterized. In the present study, we examined the biochemical properties, subcellular localization and tissue-specific distribution of Arabidopsis CML43. Our data indicate that CML43 displays characteristics typical of Ca(2+) sensors, including high-affinity Ca(2+) binding, conformational changes upon Ca(2+) binding that expose hydrophobic regions and stabilization of structure in the presence of Mg(2+) or Ca(2+). In vivo localization analysis demonstrates that CML43 resides in cytosolic and nuclear compartments. Transgenic plants expressing a CML43:GUS (β-glucoronidase) promoter reporter gene revealed that CML43 promoter activity is restricted almost exclusively to root tips under normal growth conditions. GUS reporter activity in these transgenic plants was strongly increased when exposed to the defence compound SA (salicylic acid). Furthermore, immunoblot analysis revealed that the CML43 protein accumulates following treatment with SA. Collectively, our findings suggest that CML43 functions as a Ca(2+) sensor in root tips during both normal growth and plant immune response.

Two-photon fluorescence spectroscopy and imaging of 4-dimethylaminonaphthalimide peptide and protein conjugates

We report detailed photophysical studies on the two-photon fluorescence processes of the solvatochromic fluorophore 4-DMN as a conjugate of the calmodulin (CaM) and the associated CaM-binding peptide M13. Strong two-photon fluorescence enhancement has been observed which is associated with calcium binding. It is found that the two-photon absorption cross-section is strongly dependent on the local environment surrounding the 4-DMN fluorophore in the CaM conjugates, providing sensitivity between sites of fluorophore attachment. Utilizing time-resolved measurements, the emission dynamics of 4-DMN under various environmental (solvent) conditions are analyzed. In addition, anisotropy measurements reveal that the 4-DMN-S38C-CaM system has restricted rotation in the calcium-bound calmodulin. To establish the utility for cellular imaging, two-photon fluorescence microscopy studies were also carried out with the 4-DMN-modified M13 peptide in cells. Together, these studies provide strong evidence that 4-DMN is a useful probe in two-photon imaging, with advantageous properties for cellular experiments.

Cardiac myocyte Z-line calmodulin is mainly RyR2-bound, and reduction is arrhythmogenic and occurs in heart failure

RATIONALE

Calmodulin (CaM) associates with cardiac ryanodine receptor type-2 (RyR2) as an important regulator. Defective CaM-RyR2 interaction may occur in heart failure, cardiac hypertrophy, and catecholaminergic polymorphic ventricular tachycardia. However, the in situ binding properties for CaM-RyR2 are unknown.

OBJECTIVE

We sought to measure the in situ binding affinity and kinetics for CaM-RyR2 in normal and heart failure ventricular myocytes, estimate the percentage of Z-line-localized CaM that is RyR2-bound, and test cellular function of defective CaM-RyR2 interaction.

METHODS AND RESULTS

Using fluorescence resonance energy transfer in permeabilized myocytes, we specifically resolved RyR2-bound CaM from other potential binding targets and measured CaM-RyR2 binding affinity in situ (Kd=10-20 nmol/L). Using RyR2(ADA/+) knock-in mice, in which half of the CaM-RyR2 binding is suppressed, we estimated that >90% of Z-line CaM is RyR2-bound. Functional tests indicated a higher propensity for Ca2+ wave production and stress-induced ventricular arrhythmia in RyR2(ADA/+) mice. In a post-myocardial infarction rat heart failure model, we detected a decrease in the CaM-RyR2 binding affinity (Kd≈51 nmol/L; ≈3-fold increase) and unaltered RyR2 affinity for the FK506-binding protein FKBP12.6 (Kd~0.8 nmol/L).

CONCLUSIONS

CaM binds to RyR2 with high affinity in cardiac myocytes. Physiologically, CaM is bound to >70% of RyR2 monomers and inhibits sarcoplasmic reticulum Ca2+ release. RyR2 is the major binding site for CaM along the Z-line in cardiomyocytes, and dissociating CaM from RyR2 can cause severe ventricular arrhythmia. In heart failure, RyR2 shows decreased CaM affinity, but unaltered FKBP 12.6 affinity.

A signal processing method to explore similarity in protein flexibility

Understanding mechanisms of protein flexibility is of great importance to structural biology. The ability to detect similarities between proteins and their patterns is vital in discovering new information about unknown protein functions. A Distance Constraint Model (DCM) provides a means to generate a variety of flexibility measures based on a given protein structure. Although information about mechanical properties of flexibility is critical for understanding protein function for a given protein, the question of whether certain characteristics are shared across homologous proteins is difficult to assess. For a proper assessment, a quantified measure of similarity is necessary. This paper begins to explore image processing techniques to quantify similarities in signals and images that characterize protein flexibility. The dataset considered here consists of three different families of proteins, with three proteins in each family. The similarities and differences found within flexibility measures across homologous proteins do not align with sequence-based evolutionary methods.

Molecular properties, functions, and potential applications of NAD kinases

NAD kinase catalyzes the phosphorylation of NAD(H) to form NADP(H), using ATP as phosphoryl donor. It is the only key enzyme leading to the de novo NADP(+)/NADPH biosynthesis. Coenzymes such as NAD(H) and NADP(H) are known for their important functions. Recent studies have partially demonstrated that NAD kinase plays a crucial role in the regulation of NAD(H)/NADP(H) conversion. Here, the molecular properties, physiologic functions, and potential applications of NAD kinase are discussed.

Calcium signaling in liver

In hepatocytes, hormones linked to the formation of the second messenger inositol 1,4,5-trisphosphate (InsP3) evoke transient increases or spikes in cytosolic free calcium ([Ca2+]i), that increase in frequency with the agonist concentration. These oscillatory Ca2+ signals are thought to transmit the information encoded in the extracellular stimulus to down-stream Ca2+-sensitive metabolic processes. We have utilized both confocal and wide field fluorescence microscopy techniques to study the InsP3-dependent signaling pathway at the cellular and subcellular levels in the intact perfused liver. Typically InsP3-dependent [Ca2+]i spikes manifest as Ca2+ waves that propagate throughout the entire cytoplasm and nucleus, and in the intact liver these [Ca2+]i increases are conveyed through gap junctions to encompass entire lobular units. The translobular movement of Ca2+ provides a means to coordinate the function of metabolic zones of the lobule and thus, liver function. In this article, we describe the characteristics of agonist-evoked [Ca2+]i signals in the liver and discuss possible mechanisms to explain the propagation of intercellular Ca2+ waves in the intact organ.

Calmodulin-binding proteins in the model organism Dictyostelium: a complete & critical review

Calmodulin is an essential protein in the model organism Dictyostelium discoideum. As in other organisms, this small, calcium-regulated protein mediates a diversity of cellular events including chemotaxis, spore germination, and fertilization. Calmodulin works in a calcium-dependent or -independent manner by binding to and regulating the activity of target proteins called calmodulin-binding proteins. Profiling suggests that Dictyostelium has 60 or more calmodulin-binding proteins with specific subcellular localizations. In spite of the central importance of calmodulin, the study of these target proteins is still in its infancy. Here we critically review the history and state of the art of research into all of the identified and presumptive calmodulin-binding proteins of Dictyostelium detailing what is known about each one with suggestions for future research. Two individual calmodulin-binding proteins, the classic enzyme calcineurin A (CNA; protein phosphatase 2B) and the nuclear protein nucleomorphin (NumA), which is a regulator of nuclear number, have been particularly well studied. Research on the role of calmodulin in the function and regulation of the various myosins of Dictyostelium, especially during motility and chemotaxis, suggests that this is an area in which future active study would be particularly valuable. A general, hypothetical model for the role of calmodulin in myosin regulation is proposed.

W-7 modulates Kv4.3: pore block and Ca2+-calmodulin inhibition

Ca(+)-calmodulin (Ca(2+)-CaM)-dependent protein kinase II (Ca(2+)/CaMKII) is an important regulator of cardiac ion channels, and its inhibition may be an approach for treatment of ventricular arrhythmias. Using the two-electrode voltage-clamp technique, we investigated the role of W-7, an inhibitor of Ca(2+)-occupied CaM, and KN-93, an inhibitor of Ca(2+)/CaMKII, on the K(v)4.3 channel in Xenopus laevis oocytes. W-7 caused a voltage- and concentration-dependent decrease in peak current, with IC(50) of 92.4 muM. The block was voltage dependent, with an effective electrical distance of 0.18 +/- 0.05, and use dependence was observed, suggesting that a component of W-7 inhibition of K(v)4.3 current was due to open-channel block. W-7 made recovery from open-state inactivation a biexponential process, also suggesting open-channel block. We compared the effects of W-7 with those of KN-93 after washout of 500 muM BAPTA-AM. KN-93 reduced peak current without evidence of voltage or use dependence. Both W-7 and KN-93 accelerated all components of inactivation. We used wild-type and mutated K(v)4.3 channels with mutant CaMKII consensus phosphorylation sites to examine the effects of W-7 and KN-93. In contrast to W-7, KN-93 at 35 muM selectively accelerated open-state inactivation in the wild-type vs. the mutant channel. W-7 had a significantly greater effect on recovery from inactivation in wild-type than in mutant channels. We conclude that, at certain concentrations, KN-93 selectively inhibits Ca(2+)/CaMKII activity in Xenopus oocytes and that the effects of W-7 are mediated by direct interaction with the channel pore and inhibition of Ca(2+)-CaM, as well as a change in activity of Ca(2+)-CaM-dependent enzymes, including Ca(2+)/CaMKII.

Monitoring conformational changes in protein complexes using chemical cross-linking and Fourier transform ion cyclotron resonance mass spectrometry: the effect of calcium binding on the calmodulin-melittin complex

Calmodulin is an EF hand calcium binding protein. Its binding affinities to various protein/peptide targets often depend on the conformational changes induced by the binding of calcium. One such target is melittin, which binds tightly to calmodulin in the presence of calcium, and inhibits its function. Chemical cross-linking combined with Fourier transform ion cyclotron resonance mass spectrometry has been employed to investigate the coordination of calmodulin and melittin in the complex at different concentrations of calcium. This methodology can be used to monitor structural changes of proteins induced by ligand binding, and study the effects these changes have on non- covalent interactions between proteins. Cross-linking results indicate that the binding place of the first melittin in the calcium free calmodulin form is the same as in the calcium loaded calmodulin/melittin complex.

Differential calmodulin gene expression in the nuclei of the rat midbrain-brain stem region

We investigated the expression patterns of the three calmodulin (CaM) genes, using in situ hybridization techniques, to detect gene-specific [(35)S]- and digoxigenin-labeled cRNA probes complementary to the multiple CaM mRNAs in the nuclei of the midbrain-brain stem region of the adult rat. The distinct CaM genes were widely expressed throughout this region with moderate intensities. In spite of the similar general pattern, significant differences in the distributions of the multiple CaM mRNA species were found in certain areas. In general, the CaM III mRNAs were most abundant, followed by the CaM I and CaM II mRNA populations. Most of the transcripts were found in the neuronal somata comprising the medullar nuclei, while much less label was detected in the neuropil. The CaM III mRNAs were more than 2.5 times more abundant than the CaM II mRNAs in the nucleus of the trapezoid body, and more than two times more abundant in the motor trigeminal nucleus, the principal sensory trigeminal nucleus and the olivary nucleus. The CaM III mRNAs were less dominant in the medial lemniscus, the inferior colliculus and the pontine reticular nucleus than those of the other CaM gene-specific transcripts. The CaM mRNA levels were low to moderate, without significant differences, in the mesencephalic trigeminal nucleus. The differential control of the expression of the CaM genes may contribute to the regulation of the multiple neuronal functions linked to this complex brain region and regulated by different CaM-dependent mechanisms via its target proteins.

Free and bound intracellular calmodulin measurements in cardiac myocytes

Calmodulin (CaM) is a ubiquitous Ca2+ binding protein and Ca2+-CaM activates many cellular targets and functions. While much of CaM is thought to be protein bound, quantitative data in cardiac myocytes is lacking regarding CaM location, [CaM]free and CaM redistribution during changes in [Ca2+]i. Here, we demonstrated that in adult rabbit cardiac myocytes, CaM is highly concentrated at Z-lines (confirmed by Di-8-ANEPPS staining of transverse tubules) using three different approaches: immunocytochemistry (endogenous CaM), Alexa Fluor 488 conjugate CaM (F-CaM) in both permeabilized cells (exogenous CaM) and in patch clamped intact cells (via pipette dialysis). Using 100 nM [CaM]free we washed F-CaM into permeabilized myocytes and saw a two-phase (fast and slow) CaM binding curve with a plateau after 40 min of F-CaM wash-in. We also measured myocyte [CaM]free using two modified null-point titration methods, finding [CaM]free to be 50-75 nM (which is only 1% of total [CaM]). Higher [Ca2+]i increased CaM binding especially in the nucleus and at Z-lines and significantly slowed F-CaM dissociation rate when F-CaM was washed out of permeabilized myocytes. Additionally, in both permeabilized and intact myocytes, CaM moved into the nucleus when [Ca2+]i was elevated, and this was reversible. We conclude that [CaM]free is very low in myocytes even at resting [Ca2+]i, indicating intense competition of CaM targets for free CaM. Bound CaM is relatively concentrated at Z-lines at rest but translocates significantly to the nucleus upon elevation of [Ca2+]i, which may influence activation of different targets and cellular functions.

Antipsychotic drugs disrupt normal development in Caenorhabditis elegans via additional mechanisms besides dopamine and serotonin receptors

Antipsychotic drugs may produce adverse effects during development in humans and rodents. However, the extent of these effects has not been systematically characterized nor have molecular mechanisms been identified. Consequently, we sought to evaluate the effects of an extensive panel of antipsychotic drugs in a model organism, Caenorhabditis elegans, whose development is well characterized and which offers the possibility of identifying novel molecular targets. For these studies, animals were grown from hatching in the presence of vehicle (control) or antipsychotic drugs over a range of concentrations (20-160microM) and growth was analyzed by measuring head-to-tail length at various intervals. First-generation antipsychotics (e.g., fluphenazine) generally slowed growth and maturation more than second-generation drugs such as quetiapine and olanzapine. This is consistent with in vitro effects on human neuronal cell lines. Clozapine, a second-generation drug, produced similar growth deficits as haloperidol. Converging lines of evidence, including the failure to rescue growth with high concentrations of agonists, suggested that the drug-induced delay in development was not mediated by the major neurotransmitter receptors recognized by the antipsychotic drugs. Moreover, in serotonin-deficient tph-1 mutants, the drugs dramatically slowed development and led to larval arrest (including dauer formation) and neuronal abnormalities. Evaluation of alternative targets of the antipsychotics revealed a potential role for calmodulin and underscored the significance of Ca(2+)-calmodulin signaling in development. These findings suggest that antipsychotic drugs may interfere with normal developmental processes and provide a tool for investigating the key signaling pathways involved.

Prediction of three dimensional structure of calmodulin

Calmodulin (CaM) is an important human protein, which has multiple structures. Numerous researchers studied the CaM structures in the past, and about 50 different structures in complex with fragments derived from CaM-regulated proteins have been discovered. Discovery and analysis of existing and new CaM structures is difficult due to the inherent complexity, i.e. flexibility of 6 loops and a central linker that constitute part of the CaM structure. The extensive interest in CaM structure analysis and discovery calls for a comprehensive study, which based on the accumulated expertise would design a method for prediction and analysis of future and existing CaM structures. It is also important to find the mechanisms by which the protein adjusts its structure with respect to various factors. To this end, this paper analyzes the known CaM structures and finds four factors that influence CaM structure, which include existence of Ca2+ binding, different binding segments, measuring surroundings, and sequence mutation. The degree of influence of specific factors on different structural regions is also investigated. Based on the analysis of the relation between the four factors and the corresponding CaM structure a novel method for prediction of the CaM structure in complex with novel segments, given that the surroundings of the complex, is developed. The developed prediction method is tested on a set aside, newest CaM structure. The prediction results provide useful and accurate information about the structure verifying high quality of the proposed prediction method and performed structural analysis.

Alterations of FSH-stimulated progesterone production and calcium homeostasis in primarily cultured human luteinizing-granulosa cells induced by fenvalerate

Fenvalerate, a synthetic pyrethroid, is widely used in agriculture and other domestic applications in China. Recently, Fenvalerate has been suspected to be one of the endocrine-disrupting chemicals (EDC). In this study, we investigated the effects of fenvalerate on follicle-stimulating hormone (FSH)-stimulated progesterone (P4) production by human ovarian luteinizing-granulosa cells (hGLCs). After 24 h incubation, fenvalerate inhibited FSH-stimulated P4 production. At the same time, FSH-stimulated cAMP also decreased. Due to calcium and Ca2+ -calmodulin (CaM) system involving gonadotropin-stimulated steroidogenesis by granulosa cells, we then evaluated the effects of fenvalerate on trifluoperazine (TFP)- and verapamil-driven FSH-stimulated P4 production. The results showed that calcium or calmodulin might play a role in fenvalerate-induced alterations in FSH-stimulated P4 biosynthesis. Then, the effects of fenvalerate on calcium homeostasis in hGLCs were studied. The result showed that 5 microM fenvalerate induced a slow increase in [Ca2+]i in hGLCs by using a fluorescent Ca2+ indicator fluo-3/AM. The changes in total concentration of CaM in hGLCs induced by fenvalerate were evaluated by a method of immunofluorescence. There is a significant increase in all treated groups. In summary, fenvalerate could inhibit FSH-stimulated P4 production. Also, fenvalerate interferes with calcium homeostasis in hGLCs. The effects of fenvalerate on FSH-stimulated ovarian steroidogenesis may be mediated partly through calcium signal.

Target recognition by calmodulin: the role of acid region contiguous to the calmodulin-binding domain of calcineurin A

Small-angle X-ray scattering was used to investigate the role of acid region contiguous to the calmodulin-binding domain (391-414) of calcineurin in the target recognition by calmodulin. Three synthetic peptides with the residues 385-414, 380-414 and 374-414 of calcineurin A were used for this aim. The X-ray data are consistent with the fact that calmodulin binds all three peptides with or without Ca2+. Without Ca2+, the whole peptide including acid residues interacts with dumbbell shaped calmodulin, while the acid region is extruded from globular shaped calmodulin with Ca2+. Consequently, a conformation of sequence 374-414 in calcineurin might be changed by Ca2+-signal via calmodulin, suggesting the consequence of this region with acid residues in the full activation mechanism of calcineurin by Ca2+-bound calmodulin.

Membrane trafficking of G protein-coupled receptors

G protein-coupled receptors (GPCRs) modulate diverse physiological and behavioral signaling pathways by virtue of changes in receptor activation and inactivation states. Functional changes in receptor properties include dynamic interactions with regulatory molecules and trafficking to various cellular compartments at various stages of the life cycle of a GPCR. This review focuses on trafficking of GPCRs to the cell surface, stabilization there, and agonist-regulated turnover. GPCR interactions with a variety of newly revealed partners also are reviewed with the intention of provoking further analysis of the relevance of these interactions in GPCR trafficking, signaling, or both. The disease consequences of mislocalization of GPCRs also are described.

Distinct roles of Ca2+, calmodulin, and protein kinase C in H2O2-induced activation of ERK1/2, p38 MAPK, and protein kinase B signaling in vascular smooth muscle cells

We have shown earlier that extracellular signal-regulated kinases 1 and 2 (ERK1/2) and protein kinase B (PKB), two key mediators of growth-promoting and proliferative responses, are activated by hydrogen peroxide (H(2)O(2)) in A10 vascular smooth muscle cells (VSMC). In the present studies, using a series of pharmacological inhibitors, we explored the upstream mechanisms responsible for their activation in response to H(2)O(2). H(2)O(2) treatment of VSMC stimulated ERK1/2, p38 mitogen-activated protein kinase (MAPK), and PKB phosphorylation in a dose- and time-dependent fashion. BAPTA-AM and EGTA, chelators of intracellular and extracellular Ca(2+), respectively, inhibited H(2)O(2)-stimulated ERK1/2, p38 MAPK, and PKB phosphorylation. Fluphenazine, an antagonist of the Ca(2+)-binding protein calmodulin, also suppressed the enhanced phosphorylation of ERK1/2, p38 MAPK, and PKB. In contrast, the protein kinase C (PKC) inhibitors Gö 6983 and Rö 31-8220 attenuated H(2)O(2)-induced ERK1/2 phosphorylation, but had no effect on p38 MAPK and PKB phosphorylation. Taken together, these data demonstrate that the activation of Ca(2+)/calmodulin-dependent pathways represents a key component mediating the stimulatory action of H(2)O(2) on ERK1/2, p38 MAPK, and PKB phosphorylation. On the other hand, PKC appears to be an upstream modulator of the increased ERK1/2 phosphorylation, but not of p38 MAPK and PKB in response to H(2)O(2) in VSMC.

Integrin-mediated adhesion and signaling during blastocyst implantation

Blastocyst implantation in rodents and primates depends on adhesive interactions between trophoblast cells and the endometrial extracellular matrix. As the blastocyst contacts the uterine basal lamina, cells of the trophectoderm become adhesion-competent and conclude their phenotypic conversion from a polarized epithelium to invasive trophoblast cells that anchor the embryo in the uterine wall and eventually infiltrate the endometrium. Trophoblast cells become capable of adhesion to fibronectin as alpha(5)beta(1) integrins traffick to their apical surfaces. While integrin trafficking may be required for trophoblast adhesion to the endometrium, accumulating evidence indicates that, in response to contact with the extracellular matrix, additional molecules must be recruited to the apical surface before strong adhesion is attained. Based on the known interactions of integrins with cytoplasmic regulatory proteins, we propose that extracellular matrix-bound integrins mediate intracellular signaling cascades that strengthen their adhesive activity. We will review some of the known integrin signaling pathways that could regulate trophoblast adhesion and differentiation.

Cloning and expression of the gene for a novel protein from Mycobacterium smegmatis with functional similarity to eukaryotic calmodulin

A calmodulin-like protein (CAMLP) from Mycobacterium smegmatis was purified to homogeneity and partially sequenced; these data were used to produce a full-length clone, whose DNA sequence contained a 55-amino-acid open reading frame. M. smegmatis CAMLP, expressed in Escherichia coli, exhibited properties characteristic of eukaryotic calmodulin: calcium-dependent stimulation of eukaryotic phosphodiesterase, which was inhibited by the calmodulin antagonist trifluoperazine, and reaction with anti-bovine brain calmodulin antibodies. Consistent with the presence of nine acidic amino acids (16%) in M. smegmatis CAMLP, there is one putative calcium-binding domain in this CAMLP, compared to four such domains for eukaryotic calmodulin, reflecting the smaller molecular size (approximately 6 kDa) of M. smegmatis CAMLP. Ultracentrifugation and mass spectral studies excluded the possibility that calcium promotes oligomerization of purified M. smegmatis CAMLP.