Role Of Ca2 Research Articles

The Connections between Atrial Fibrillation and Mental Disorders: Role of Ca2+/cAMP Signalling

The Connections between Atrial Fibrillation and Mental Disorders: Role of Ca2+/cAMP Signalling

Analyzing Mitochondrial Calcium Influx in Isolated Mitochondria.

Mitochondria play a crucial role in Ca2+ signaling and homeostasis and can contribute to shaping the cytosolic Ca2+ landscape as well as regulate a variety of pathways including energy production and cell death. Dysregulation of mitochondrial Ca2+ homeostasis promotes pathologies including neurodegenerative diseases, cardiovascular disorders, and metabolic syndromes. The significance of mitochondria to Ca2+ signaling and regulation underscores the value of methods to assess mitochondrial Ca2+ import. Here we present a plate reader-based method using the Ca2+-sensitive fluorescent probe calcium green-5N to measure mitochondrial Ca2+ import in isolated cardiac mitochondria. This technique can be expanded to measure Ca2+ uptake in mitochondria isolated from other tissue types and from cultured cells.

Role of Ca in Ni-Ca/Fumed-SiO2 Catalysts for CO2 Catalytic Conversion to Methane

AbstractThis study investigates the role of calcium in facilitating the carbon dioxide methanation reaction over nickel supported on fumed-SiO2 catalysts. The wet impregnation method was used to prepare Ni/fumed-SiO2 catalysts with three different Ca loadings for CO2 conversion. As part of the investigation into the effects of Ca concentration and reaction conditions on the structural and morphological properties of the catalysts, various techniques including XRD, BET, SEM, TPR and TEM were used for both fresh and used catalyst samples. The findings showed that the addition of 0.5% Ca increases the catalyst reducibility, promotes dispersion of Ni sites on the surface of fumed SiO2 support and prevents the metal from agglomerating. Evaluation of catalytic results showed that the performance of 10%Ni-0.5Ca/fumed-SiO2 was superior to the other tested catalysts, with CO2 conversion and CH4 yield of 76% and ~ 40% at 650 °C, respectively.

Cadmium and calcium ions' effects on the growth of Pleurotus ostreatus mycelia are related to phosphatidylethanolamine content

Heavy metal Cd2+ can easily be accumulated by fungi, causing significant stress, with the fungal cell membrane being one of the primary targets. However, the understanding of the mechanisms behind this stress remains limited. This study investigated the changes in membrane lipid molecules of Pleurotus ostreatus mycelia under Cd2+ stress and the antagonistic effect of Ca2+ on this stress. Cd2+ in the growth media significantly inhibited mycelial growth, with increasing intensity at higher concentrations. The addition of Ca2+ mitigated this Cd2+-induced growth inhibition. Lipidomic analysis showed that Cd2+ reduced membrane lipid content and altered lipid composition, while Ca2+ counteracted these changes. The effects of both Cd2+ and Ca2+ on lipids are dose dependent and phosphatidylethanolamine appeared most affected. Cd2+ also caused a phosphatidylcholine/phosphatidylethanolamine ratio increase at high concentrations, but Ca2+ helped maintain normal levels. The acyl chain length and unsaturation of lipids remained unaffected, suggesting Cd2+ doesn't alter acyl chain structure of lipids. These findings suggest that Cd2+ may affect the growth of mycelia by inhibiting the synthesis of membrane lipids, particular the synthesis of phosphatidylethanolamine, providing novel insights into the mechanisms of Cd2+ stress in fungi and the role of Ca2+ in mitigating the stress.

Calcium Rescues Streptococcus pneumoniae D39 ΔmntE Manganese-Sensitive Growth Phenotype.

Calcium (Ca2+) functions as a universal signal messenger in eukaryotes but in bacteria, the physiological roles for Ca2+ are limited. Here, we examine the role of Ca2+ in Streptococcus pneumoniae during manganese (Mn2+) intoxication. S. pneumoniae mntE mutants, lacking the Mn2+ efflux transporter, exhibit impaired growth due to accumulation of Mn2+ when exposed to elevated exogenous Mn2+. This Mn2+-sensitive growth defect is restored to wild-type growth level by exogenous Ca2+, in a Ca2+-dependent manner. Despite growth restoration of the mntE mutant to wild-type levels, cellular Mn2+ remains elevated in this strain. Bacterial capsule production is also increased for the mntE mutant, resulting in reduced adherence capacity to surfaces and poor biofilm formation, which is consistent with it experiencing Mn2+ intoxication. Ca2+ presence did not significantly impact bacterial capsule production or biofilm formation. Further analysis of the cell morphology demonstrates that Ca2+ contributes to cell division and reduces cell chain lengths. Together, these data describe the first role of Ca in S. pneumoniae that has potential implications in bacterial virulence since Ca affects cell division and likely Mn2+-associated cellular processes.

LaCo0.2Fe0.8O3 perovskites doped with natural Ca2+ as bifunctional electrocatalysts for oxygen evolution and reduction reactions.

Perovskite oxides are promising electrocatalysts for various energy applications due to their exceptional catalytic activity, flexible architecture, and low cost. In this study, LCFO was doped with different ratios of Ca2+ from eggshells, resulting in dual-purpose electrocatalysts for oxygen reduction and evolution processes. The nanoparticles were characterized using various techniques, including Brunauer-Emmett-Teller analysis and XRD. Results clarified the relative surface area and roughness, increasing with Ca2+ doping. LCFO also demonstrated highly magnetic properties, improved charge transfer, catalytic activity, and long-term durability. The results demonstrated the perovskite's cost-effectiveness as a bifunctional electrocatalyst, and the role of Ca2+ in enhancing its properties. La0.6Ca0.4Co0.2Fe0.8O3(LCCFO-0.4) showed higher magnetic properties (M s = 13.36 emu g-1 and M r = 2.54 emu g-1). The LCFO sample showed a current density of 5.13 mA cm-2 and 3 mA cm-2 for OER and ORR respectively, at E onset 1.7 V and 0.57 V (vs. RHE). The LCFO electrochemical active surface area is 0.033 cm2.

Orai1 and Orai3 act through distinct signalling axes to promote stemness and tumorigenicity of breast cancer stem cells

BackgroundOne of major challenges in breast tumor therapy is the existence of breast cancer stem cells (BCSCs). BCSCs are a small subpopulation of tumor cells that exhibit characteristics of stem cells. BCSCs are responsible for progression, recurrence, chemoresistance and metastasis of breast cancer. Ca2+ signalling plays an important role in diverse processes in cancer development. However, the role of Ca2+ signalling in BCSCs is still poorly understood.MethodsA highly effective 3D soft fibrin gel system was used to enrich BCSC-like cells from ER+ breast cancer lines MCF7 and MDA-MB-415. We then investigated the role of two Ca2+-permeable ion channels Orai1 and Orai3 in the growth and stemness of BCSC-like cells in vitro, and tumorigenicity in female NOD/SCID mice in vivo.ResultsOrai1 RNA silencing and pharmacological inhibition reduced the growth of BCSC-like cells in tumor spheroids, decreased the expression levels of BCSC markers, and reduced the growth of tumor xenografts in NOD/SCID mice. Orai3 RNA silencing also had similar inhibitory effect on the growth and stemness of BCSC-like cells in vitro, and tumor xenograft growth in vivo. Mechanistically, Orai1 and SPCA2 mediate store-operated Ca2+ entry. Knockdown of Orai1 or SPCA2 inhibited glycolysis pathway, whereas knockdown of Orai3 or STIM1 had no effect on glycolysis.ConclusionWe found that Orai1 interacts with SPCA2 to mediate store-independent Ca2+ entry, subsequently promoting the growth and tumorigenicity of BCSC-like cells via glycolysis pathway. In contrast, Orai3 and STIM1 mediate store-operated Ca2+ entry, promoting the growth and tumorigenicity of BCSC-like cells via a glycolysis-independent pathway. Together, our study uncovered a well-orchestrated mechanism through which two Ca2+ entry pathways act through distinct signalling axes to finely control the growth and tumorigenicity of BCSCs.

High-performance ultra-lean biodegradable Mg–Ca alloys and guidelines for their processing

High-performance ultra-lean binary Mg–Ca alloys are engineered by intelligent alloying and thermo-mechanical processing using hot-extrusion. With Ca-alloying contents as low as 0.2-0.6 wt.%, remarkable room-temperature tensile properties are obtained with tensile strength values as high as 380–420 MPa, or ductility values reaching a maximum of 36 %. By means of multiscale structural and chemical analysis using electron microscopy and energy dispersive X-ray spectroscopy, we show that multimodal strengthening mechanisms can be activated by modifying the spatial distribution of Ca as secondary phase. Our results indicate that strong precipitation strengthening is achieved when Mg2Ca phase particles are dispersed within the grains. On the other hand, preferential distribution of the Mg2Ca precipitates along grain boundaries imparts substantial grain-boundary strengthening by the Hall-Petch effect. Apart from secondary-phase precipitation, the role of Ca as solute atoms is paramount in promoting homogeneous deformation. The presence of Ca directly alters the intrinsic stacking fault energies and modifies the cross-slip energy barriers such that the slip-transition probability from pyramidal-to-basal and vice-versa becomes comparable. Both effects ensure competitive activation of basal and non-basal slip, thereby reducing the mechanical anisotropy. The mechanical performance in the current work, when compared to earlier reported studies of Mg alloys with similar or higher alloying content, shows a 2 to 10-fold increase in tensile strength without compromising ductility.

Structural characteristics and gelling properties of citrus pectins after chemical and enzymatic modifications: Conformation plays a vital role in Ca2+-induced gelation

Due to the excellent health benefits of rhamnogalacturonan I (RG-I)-enriched pectin, there has been increasing research interest in its gelling properties. To elucidate its structure–gelation relationship, chemical modifications were used to obtain RG-I-enriched pectin (P11). Then, enzymatic modification was performed to obtain debranched pectins GP11 and AP11, respectively. The effects of RG-I side chains on structural characteristics (especially spatial conformation) and gelling properties were investigated. Among the low-methoxylated pectins (LMPs), AP11, with a loose conformation (Dmax 52 nm) showed the poorest gelling, followed by GP11. In addition to primary structure, spatial conformation (Dmax and Rg) also showed strong correlations (r2 > 0.8) with gelation. We speculate that compact conformation may shorten distance between pectin chains and reduces steric hindrance, contributing to formation of strong gel network. This is particularly important in LMPs with abundant side chains. The results provide novel insights into relationship between spatial conformation and gelling properties of RG-I-enriched pectin.

P-type calcium ATPases play important roles in biotic and abiotic stress signaling.

Knowledge of Ca2+-ATPases is imperative for improving crop quality/ food security, highly threatened due to global warming. Ca2+-ATPases modulates calcium, essential for stress signaling and modulating growth, development, and immune activities. Calcium is considered a versatile secondary messenger and essential for short- and long-term responses to biotic and abiotic stresses in plants. Coordinated transport activities from both calcium influx and efflux channels are required to generate cellular calcium signals. Various extracellular stimuli cause an induction in cytosolic calcium levels. To cope with such stresses, it is important to maintain intracellular Ca2+ levels. Plants need to evolve efficient efflux mechanisms to maintain Ca2+ ion homeostasis. Plant Ca2+-ATPases are members of the P-type ATPase superfamily and localized in the plasma membrane and endoplasmic reticulum (ER). They are required for various cellular processes, including plant growth, development, calcium signaling, and even retorts to environmental stress. These ATPases play an essential role in Ca2+ homeostasis and are actively involved in Ca2+ transport. Plant Ca2+-ATPases are categorized into two major classes: type IIA and type IIB. Although these two classes of ATPases share similarities in protein sequence, they differ in their structure, cellular localization, and sensitivity to inhibitors. Due to the emerging role of Ca2+-ATPase in abiotic and biotic plant stress, members of this family may help promote agricultural improvement under stress conditions. This review provides a comprehensive overview of P-type Ca2+-ATPase, and their role in Ca2+ transport, stress signaling, and cellular homeostasis focusing on their classification, evolution, ion specificities, and catalytic mechanisms. It also describes the main aspects of the role of Ca2+-ATPase in transducing signals during plant biotic and abiotic stress responses and its role in plant development and physiology.

Structural insights into the regulation of RyR1 by S100A1

S100A1, a small homodimeric EF-hand Ca2+-binding protein (~21 kDa), plays an important regulatory role in Ca2+ signaling pathways involved in various biological functions including Ca2+ cycling and contractile performance in skeletal and cardiac myocytes. One key target of the S100A1 interactome is the ryanodine receptor (RyR), a huge homotetrameric Ca2+ release channel (~2.3 MDa) of the sarcoplasmic reticulum. Here, we report cryoelectron microscopy structures of S100A1 bound to RyR1, the skeletal muscle isoform, in absence and presence of Ca2+. Ca2+-free apo-S100A1 binds beneath the bridging solenoid (BSol) and forms contacts with the junctional solenoid and the shell-core linker of RyR1. Upon Ca2+-binding, S100A1 undergoes a conformational change resulting in the exposure of the hydrophobic pocket known to serve as a major interaction site of S100A1. Through interactions of the hydrophobic pocket with RyR1, Ca2+-bound S100A1 intrudes deeper into the RyR1 structure beneath BSol than the apo-form and induces sideways motions of the C-terminal BSol region toward the adjacent RyR1 protomer resulting in tighter interprotomer contacts. Interestingly, the second hydrophobic pocket of the S100A1-dimer is largely exposed at the hydrophilic surface making it prone to interactions with the local environment, suggesting that S100A1 could be involved in forming larger heterocomplexes of RyRs with other protein partners. Since S100A1 interactions stabilizing BSol are implicated in the regulation of RyR-mediated Ca2+ release, the characterization of the S100A1 binding site conserved between RyR isoforms may provide the structural basis for the development of therapeutic strategies regarding treatments of RyR-related disorders.

Catalysts with Trimetallic Sites on Graphene-like C2N for Electrocatalytic Nitrogen Reduction Reaction: A Theoretical Investigation.

Electrocatalytic nitrogen reduction reaction (NRR) is a green and highly efficient way to replace the industrial Haber-Bosch process. Herein, clusters consisting of three transition metal atoms loaded on C2N as NRR electrocatalysts are investigated using density functional theory (DFT). Meanwhile, Ca was introduced as a promoter and the role of Ca in NRR was investigated. It was found that Ca anchored to the catalyst can act as an electron donor and effectively promote the activation of N2 on M3. In both M3@C2N and M3Ca@C2N (M=Fe, Co, Ni), the limiting potential (UL) is less negative than that of the Ru(0001) surface and has the ability to suppress the competitive hydrogen evolution reaction (HER). Among them, Fe3@C2N is suggested to be the most promising candidate for NRR with high thermal stability, strong N2 adsorption ability, low limiting potential, and good NRR selectivity. The concepts of trimetallic sites and alkaline earth metal promoters in this work provide theoretical guidance for the rational design of atomically active sites in electrocatalytic NRR.

The role of calcium stores in long-term potentiation and synaptic tagging and capture in mouse hippocampus.

The roles of Ca2+-induced calcium release in synaptic plasticity and metaplasticity are poorly understood. The present study has addressed the role of intracellular Ca2+ stores in long-term potentiation (LTP) and a form of heterosynaptic metaplasticity known as synaptic tagging and capture (STC) at CA1 synapses in mouse hippocampal slices. The effects of two compounds, ryanodine and cyclopiazonic acid (CPA), were examined on LTP induced by three distinct induction protocols: weak (w), compressed (c) and spaced (s) theta-burst stimulation (TBS). These compounds did not significantly affect LTP induced by the wTBS (one episode of TBS; 25 stimuli) or cTBS (three such episodes with a 10 s inter-episode interval (IEI); 75 stimuli) but substantially inhibited LTP induced by a sTBS (10 min IEI; 75 stimuli). Ryanodine and CPA also prevented a small heterosynaptic potentiation that was observed with the sTBS protocol. Interestingly, these compounds also prevented STC when present during either the sTBS or the subsequent wTBS, applied to an independent input. All of these effects of ryanodine and CPA were similar to that of a calcium-permeable AMPA receptor blocker. In conclusion, Ca2+ stores provide one way in which signals are propagated between synaptic inputs and, by virtue of their role in STC, may be involved in associative long-term memories. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Early screening and staging of melanoma using blood based on laser-induced breakdown spectroscopy

For melanoma, early screening could increase the cure rate, while staging helps to make treatment strategies. Blood sampling has advantages of little damage, convenient operation and low cost, which combined with laser-induced breakdown spectroscopy (LIBS) has been utilized for tumor diagnoses. Here, we proposed to accurately attain early screening and staging of melanoma blood using LIBS. The serum was collected from 25 melanoma mice and 10 healthy controls on the 7th, 14th, 21st and 28th days. Compared with k nearest neighbor (kNN), support vector machine (SVM) and back propagation neural network (BPNN) models, the adaptive boosting of BPNN (BP_AdaBoost) models had the best accuracies of 83.37 % for early screening and 96.18 % for staging, respectively. Using mutual information (MI) method to select features, the accuracies of BP_AdaBoost models were improved to 86.11 % for early screening and 96.91 % for staging, respectively. Besides, the difference significance of elements and molecular bands in the serum was examined by the Kruskal-Wallis (K-W) test. The test results showed that obvious differences of Ca and Na existed in both early screening and staging, while K and Mg made significant differences in staging, consistent with roles of Ca and Na in the whole process of tumor development and roles of K and Mg in tumor proliferation and metastasis. Overall, all results demonstrated that early screening and staging of melanoma could be accurately realized using blood based on LIBS.

Rcn1, the fission yeast homolog of human DSCR1, regulates arsenite tolerance independently from calcineurin.

Calcineurin (CN) is a conserved Ca2+/calmodulin-dependent phosphoprotein phosphatase that plays a key role in Ca2+ signaling. Regulator of calcineurin 1 (RCAN1), also known as Down syndrome critical region gene 1 (DSCR1), interacts with calcineurin and inhibits calcineurin-dependent signaling in various organisms. Ppb1, the fission yeast calcineurin regulates Cl--homeostasis, and Ppb1 deletion induces MgCl2 hypersensitivity. Here, we characterize the conserved and novel roles of the fission yeast RCAN1 homolog rcn1+. Consistent with its role as an endogenous calcineurin inhibitor, Rcn1 overproduction reproduced the calcineurin-null phenotypes, including MgCl2 hypersensitivity and inhibition of calcineurin signaling upon extracellular Ca2+ stimuli as evaluated by the nuclear translocation and transcriptional activation of the calcineurin substrate Prz1. Notably, overexpression of rcn1+ causes hypersensitivity to arsenite, whereas calcineurin deletion induces arsenite tolerance, showing a phenotypic discrepancy between Rcn1 overexpression and calcineurin deletion. Importantly, although Rcn1 deletion induces modest sensitivities to arsenite and MgCl2 in wild-type cells, the arsenite tolerance, but not MgCl2 sensitivity, associated with Ppb1 deletion was markedly suppressed by Rcn1 deletion. Collectively, our findings reveal a previously unrecognized functional collaboration between Rcn1 and calcineurin, wherein Rcn1 not only negatively regulates calcineurin in the Cl- homeostasis, but also Rcn1 mediates calcineurin signaling to modulate arsenite cytotoxicity.

The role of Ca2+ signalling and InsP3R in the pathogenesis of intrahepatic cholestasis of pregnancy

Background In order to contribute new insights for future prevention and treatment of intrahepatic cholestasis of pregnancy (ICP), and to promote positive pregnancy outcomes, we evaluated serum Ca2+ levels and inositol 1,4,5-trisphosphate receptor (InsP3R) expression in the liver tissue of a rat ICP model. Methods After establishing the model by injection of oestradiol benzoate and progesterone into pregnant rats, animals were divided into normal control (n = 5) and ICP model groups (n = 5). The expression of InsP3R protein in the liver, and serum levels of Ca2+, glycocholic acid and bile acid were detected. Results InsP3R mRNA and protein were significantly lower in the ICP model group compared to the normal group, as determined by qPCR and immunohistochemistry, respectively. Serum enzyme-linked immunosorbent assay results revealed significantly higher levels of glycocholic acid and bile acid in the ICP model group compared to the normal group, while Ca2+ levels were significantly lower. The levers of Ca2+ were significantly and negatively correlated with the levels of glycocholic acid. The observed decrease in Ca2+ was associated with an increase in total bile acids, but there was no significant correlation. Conclusions Our results revealed that the expression of InsP3R and serum Ca2+ levels was significantly decreased in the liver tissue of ICP model rats. Additionally, Ca2+ levels were found to be negatively correlated with the level of glycocholic acid.

10th European Calcium Society symposium: The Ca2+-signaling toolkit in cell function, health and disease.

The 10th European Calcium Society symposium, organized in Leuven, Belgium on November 15-17, 2023, focused on the role of Ca2+ signaling in cell function, health and disease. The symposium featured six scientific sessions, 16 invited speakers - of whom two were postdoctoral researchers - and 14 short talks. The talks covered various aspects of intracellular Ca2+ signaling and its implications in pathology. Each session was opened by one or more invited speakers, followed by a series of presentations from speakers selected from submitted abstracts. Through short talks, poster presentations, awards, and sustainable travel fellowships, the symposium also fostered opportunities for the active participation of early-career researchers. At least half of the short talks were allocated to early-career researchers, thereby offering a platform for the presentation of ongoing work and unpublished results. Presentations were also broadcast in real-time for online attendees. In this Meeting Review, we aim to capture the spirit of the meeting and discuss the main take-home messages that emerged during the symposium.

Unraveling the intrinsic mechanism behind the retention of arsenic in the co-gasification of coal and sewage sludge: Focus on the role of Ca and Fe compounds

Minimizing the emission of arsenic (As) is one of the urgent problems during co-gasification of Shenmu coal (SM) and sewage sludge (SS). The intrinsic mechanism of As retention was obtained by analyzing the effect of different SM addition ratios on the As form transformation during co-gasification at 1000 °C under CO2 atmosphere. The results showed that the addition of SM effectively promoted the enrichment of As in the co-gasified residues. Especially, the best As retention rate of 65.71% was achieved with the 70 wt% addition ratio of SM. The addition of SM promoted the adsorption and chemical oxidation of As(III) to the less toxic As(V) through the coupling of Ca and Fe compounds in the co-gasified residues. XRD and XPS results indicated that Fe2O3 adsorbed As2O3(g) after partial conversion to Fe3O4 by the Boudouard reaction, while part of As2O3 was oxidized to As2O5 by lattice oxygen. Finally, the generated As2O5 was successively trapped by CaO and Fe2O3 to form stable Ca3(AsO4)2 and FeAsO4. HRTEM and TEM analysis comprehensively proved that As(III) was stabilized by the lattice cage of CaAl2Si2O8. In conclusion, the co-oxidation of Ca and Fe compounds and lattice stabilization simultaneously played a crucial role in the retention of As2O3(g) during co-gasification.

First-principles investigation on adsorption poisoning and heterogeneous nucleation mechanisms in Ca modified primary Mg2Si phase

We employed first-principles calculations to investigate the adsorption poisoning and heteroepitaxial nucleation mechanisms in the Ca modification of the primary Mg2Si phase. The extensive computations considering various factors such as lattice mismatch, interface energy, adsorption energy, charge density, work of adhesion, and interface mechanical properties, as well as comparisons of interface stacking modes reveal that Ca modification of the primary Mg2Si phase can occur through both adsorption poisoning and heteroepitaxial nucleation mechanisms simultaneously. The adsorption poisoning mechanism implies that Ca preferentially adsorbs on the Mg-terminated surfaces of Mg2Si(100) and Mg2Si(111). Meanwhile, the heteroepitaxial nucleation mechanism indicates the nucleation interface of Mg2Si(100)//CaSi2(001), where the Mg2Si(100) surface is terminated by Si, and the CaSi2(001) surface is terminated by Ca, with stacking modes of Si-Top and Si-Center. In addition, the inclusion of Ca in the primary Mg2Si phase through heteroepitaxial nucleation not only leads to refinement of the primary Mg2Si phase but also displays excellent interface mechanical properties, which suggests that Ca can be considered as an optimal modifier for the primary Mg2Si phase. This study provides a fundamental insight into the role of Ca in modifying the primary Mg2Si phase and has potential implications for the development of Si-containing magnesium alloys.

Phospholipids Differentially Regulate Ca2+ Binding to Synaptotagmin-1.

Synaptotagmin-1 (Syt-1) is a calcium sensing protein that is resident in synaptic vesicles. It is well established that Syt-1 is essential for fast and synchronous neurotransmitter release. However, the role of Ca2+ and phospholipid binding in the function of Syt-1, and ultimately in neurotransmitter release, is unclear. Here, we investigate the binding of Ca2+ to Syt-1, first in the absence of lipids, using native mass spectrometry to evaluate individual binding affinities. Syt-1 binds to one Ca2+ with a KD ∼ 45 μM. Each subsequent binding affinity (n ≥ 2) is successively unfavorable. Given that Syt-1 has been reported to bind anionic phospholipids to modulate the Ca2+ binding affinity, we explored the extent that Ca2+ binding was mediated by selected anionic phospholipid binding. We found that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and dioleoylphosphatidylserine (DOPS) positively modulated Ca2+ binding. However, the extent of Syt-1 binding to phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) was reduced with increasing [Ca2+]. Overall, we find that specific lipids differentially modulate Ca2+ binding. Given that these lipids are enriched in different subcellular compartments and therefore may interact with Syt-1 at different stages of the synaptic vesicle cycle, we propose a regulatory mechanism involving Syt-1, Ca2+, and anionic phospholipids that may also control some aspects of vesicular exocytosis.