Synergistic effects of putative Ca2+-binding sites of calmodulin in fungal development, temperature stress and virulence of Aspergillus fumigatus

In pathogenic fungi, calcium-calmodulin-dependent serine-threonine-specific phosphatase calcineurin is involved in morphogenesis and virulence. Therefore, calcineurin and its tightly related protein complexes are attractive antifungal drug targets. However, there is limited knowledge available on the relationship between in vivo Ca2+-binding sites of calmodulin (CaM) and its functions in regulating stress responses, morphogenesis, and pathogenesis. In the current study, we demonstrated that calmodulin is required for hyphal growth, conidiation, and virulence in the human fungal pathogen, Aspergillus fumigatus. Site-directed mutations of calmodulin revealed that a single Ca2+-binding site mutation had no significant effect on A. fumigatus hyphal development, but multiple Ca2+-binding site mutations exhibited synergistic effects, especially when cultured at 42 °C, indicating that calmodulin function in response to temperature stress depends on its Ca2+-binding sites. Western blotting implied that mutations in Ca2+-binding sites caused highly degraded calmodulin fragments, suggesting that the loss of Ca2+-binding sites results in reduced protein stability. Moreover, normal intracellular calcium homeostasis and the nuclear translocation of the transcriptional factor CrzA are dependent on Ca2+-binding sites of AfCaM, demonstrating that Ca2+-binding sites of calmodulin are required for calcium signalling and its major transcription factor CrzA. Importantly, in situ mutations for four Ca2+-binding sites of calmodulin resulted in an almost complete loss of virulence in the Galleria mellonella wax moth model. This study shed more light on the functional characterization of putative calcium-binding sites of calmodulin in the morphogenesis and virulence of A. fumigatus, which enhances our understanding of calmodulin biological functions in cells of opportunistic fungal pathogens.

The nematode effector calreticulin competes with the high mobility group protein OsHMGB1 for binding to the rice calmodulin-like protein OsCML31 to enhance rice susceptibility to Meloidogyne graminicola

The root-knot nematode Meloidogyne graminicola secretes effectors into rice tissues to modulate host immunity. Here, we characterised MgCRT1, a calreticulin protein of M. graminicola, and identified its target in the plant. In situ hybridisation showed MgCRT1 mRNA accumulating in the subventral oesophageal gland in J2 nematodes. Immunolocalization indicated MgCRT1 localises in the giant cells during parasitism. Host-induced gene silencing of MgCRT1 reduced the infection ability of M. graminicola, while over-expressing MgCRT1 enhanced rice susceptibility to M. graminicola. A yeast two-hybrid approach identified the calmodulin-like protein OsCML31 as an interactor of MgCRT1. OsCML31 interacts with the high mobility group protein OsHMGB1 which is a conserved DNA binding protein. Knockout of OsCML31 or overexpression of OsHMGB1 in rice results in enhanced susceptibility to M. graminicola. In contrast, overexpression of OsCML31 or knockout of OsHMGB1 in rice decreases susceptibility to M. graminicola. The GST-pulldown and luciferase complementation imaging assay showed that MgCRT1 decreases the interaction of OsCML31 and OsHMGB1 in a competitive manner. In conclusion, when M. graminicola infects rice and secretes MgCRT1 into rice, MgCRT1 interacts with OsCML31 and decreases the association of OsCML31 with OsHMGB1, resulting in the release of OsHMGB1 to enhance rice susceptibility.

Understanding the pathogenic significance of altered calcium-calmodulin signaling in T cells in autoimmune diseases

Calcium/calmodulin-dependent protein kinase IV (CaMK4) serves as a pivotal mediator in the regulation of gene expression, influencing the activity of transcription factors within a variety of immune cells, including T cells. Altered CaMK4 signaling is implicated in autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and psoriasis, which are characterized by dysregulated immune responses and clinical complexity. These conditions share common disturbances in immune cell functionality, cytokine production, and autoantibody generation, all of which are associated with disrupted calcium-calmodulin signaling. This review underscores the consequences of dysregulated CaMK4 signaling across these diseases, with an emphasis on its impact on Th17 differentiation and T cell metabolism-processes central to maintaining immune homeostasis. A comprehensive understanding of roles of CaMK4 in gene regulation across various autoimmune disorders holds promise for the development of targeted therapies, particularly for diseases driven by Th17 cell dysregulation.

Control of Munc13-1 Activity by Autoinhibitory Interactions Involving the Variable N-terminal Region

Regulation of neurotransmitter release during presynaptic plasticity underlies varied forms of information processing in the brain. Munc13s play essential roles in release via their conserved C-terminal region, which contains a MUN domain involved in SNARE complex assembly, and controls multiple presynaptic plasticity processes. Munc13s also have a variable N-terminal region, which in Munc13-1 includes a calmodulin binding (CaMb) domain involved in short-term plasticity and a C2A domain that forms an inhibitory homodimer. The C2A domain is activated by forming a heterodimer with the zinc-finger domain of αRIMs, providing a link to αRIM-dependent short- and long-term plasticity. However, it is unknown how the functions of the N- and C-terminal regions are integrated, in part because of the difficulty of purifying Munc13-1 fragments containing both regions. We describe for the first time the purification of a Munc13-1 fragment spanning its entire sequence except for a flexible region between the C2A and CaMb domains. We show that this fragment is much less active than the Munc13-1 C-terminal region in liposome fusion assays and that its activity is strongly enhanced by the RIM2α zinc-finger domain together with calmodulin. NMR experiments show that the C2A and CaMb domains bind to the MUN domain and that these interactions are relieved by the RIM2α ZF domain and calmodulin, respectively. These results suggest a model whereby Munc13-1 activity in promoting SNARE complex assembly and neurotransmitter release are inhibited by interactions of the C2A and CaMb domains with the MUN domain that are relieved by αRIMs and calmodulin.

Functional characterization of calmodulin-like proteins, CML13 and CML14, as novel light chains of Arabidopsis class VIII myosins

Myosins are important motor proteins that associate with the actin cytoskeleton. Structurally, myosins function as heteromeric complexes where smaller light chains, such as calmodulin (CaM), bind to isoleucine-glutamine (IQ) domains in the neck region to facilitate mechano-enzymatic activity. We recently identified Arabidopsis CaM-like (CML) proteins CML13 and CML14 as interactors of proteins containing multiple IQ domains, including a myosin VIII. Here, we demonstrate that CaM, CML13, and CML14 bind the neck region of all four Arabidopsis myosin VIII isoforms. Among CMLs tested for binding to myosins VIIIs, CaM, CML13, and CML14 gave the strongest signals using in planta split-luciferase protein interaction assays. In vitro, recombinant CaM, CML13, and CML14 showed specific, high-affinity, calcium-independent binding to the IQ domains of myosin VIIIs. CaM, CML13, and CML14 co-localized to plasma membrane-bound puncta when co-expressed with red fluorescent protein-myosin fusion proteins containing IQ and tail domains of myosin VIIIs. In vitro actin motility assays using recombinant myosin VIIIs demonstrated that CaM, CML13, and CML14 function as light chains. Suppression of CML13 or CML14 expression using RNA silencing resulted in a shortened-hypocotyl phenotype, similar to that observed in a quadruple myosin mutant, myosin viii4KO. Collectively, our data indicate that Arabidopsis CML13 and CML14 are novel myosin VIII light chains.

The Calmodulin-interacting peptide Pcp4a regulates feeding state-dependent behavioral choice in zebrafish

Animals constantly need to judge the valence of an object in their environment: is it potential food or a threat? The brain makes fundamental decisions on the appropriate behavioral strategy by integrating external information from sensory organs and internal signals related to physiological needs. For example, a hungry animal may take more risks than a satiated one when deciding to approach or avoid an object. Using a proteomic profiling approach, we identified the Calmodulin-interacting peptide Pcp4a as a key regulator of foraging-related decisions. Food intake reduced abundance of protein and mRNA of pcp4a via dopamine D2-like receptor-mediated repression of adenylate cyclase. Accordingly, deleting the pcp4a gene made zebrafish larvae more risk averse in a binary decision assay. Strikingly, neurons in the tectum became less responsive to prey-like visual stimuli in pcp4a mutants, thus biasing the behavior toward avoidance. This study pinpoints a molecular mechanism modulating behavioral choice according to internal state.

TRPV4-dependent Ca2+ influx determines cholesterol dynamics at the plasma membrane

The activities of the transient receptor potential vanilloid 4 (TRPV4), a Ca2+-permeable nonselective cation channel, are controlled by its surrounding membrane lipids (e.g., cholesterol, phosphoinositides). The transmembrane region of TRPV4 contains a cholesterol recognition amino acid consensus (CRAC) motif and its inverted (CARC) motif located in the plasmalemmal cytosolic leaflet. TRPV4 localizes in caveolae, a bulb-shaped cholesterol-rich domain at the plasma membrane. Here, we visualized the spatiotemporal interactions between TRPV4 and cholesterol at the plasma membrane in living cells by dual-color single-molecule imaging using total internal reflection fluorescence microscopy. To this aim, we labeled cholesterol at the cytosolic leaflets of the plasma membrane using a cholesterol biosensor, D4H. Our single-molecule tracking analysis showed that the TRPV4 molecules colocalize with D4H-accessible cholesterol molecules mainly in the low fluidity membrane domains in which both molecules are highly clustered. Colocalization of TRPV4 and D4H-accessible cholesterol was observed both inside and outside of caveolae. Agonist-evoked TRPV4 activation remarkably decreased colocalization probability and association rate between TRPV4 and D4H-accessible cholesterol molecules. Interestingly, upon TRPV4 activation, the particle density of D4H-accessible cholesterol molecules was decreased and the D4H-accessible cholesterol molecules in the fast-diffusing state were increased at the plasma membrane. The introduction of skeletal dysplasia-associated R616Q mutation into the CRAC/CARC motif of TRPV4, which reduced the interaction with cholesterol clusters, could not alter the D4H-accessible cholesterol dynamics. Mechanistically, TRPV4-mediated Ca2+ influx and the C-terminal calmodulin-binding site of TRPV4 are essential for modulating the plasmalemmal D4H-accessible cholesterol dynamics. We propose that TRPV4 remodels its surrounding plasmalemmal environment by manipulating cholesterol dynamics through Ca2+ influx.

Real-time single-molecule imaging of CaMKII-calmodulin interactions

The binding of calcium/calmodulin (CAM) to calcium/calmodulin-dependent protein kinase II (CaMKII) initiates an ATP-driven cascade that triggers CaMKII autophosphorylation. The autophosphorylation in turn increases the CaMKII affinity for CAM. Here, we studied the ATP dependence of CAM association with the actin-binding CaMKIIβ isoform using single-molecule total internal reflection fluorescence microscopy. Rhodamine-CAM associations/dissociations to surface-immobilized Venus-CaMKIIβ were resolved with 0.5 s resolution from video records, batch-processed with a custom algorithm. CAM occupancy was determined simultaneously with spot-photobleaching measurement of CaMKII holoenzyme stoichiometry. We show the ATP-dependent increase of the CAM association requires dimer formation for both the α and β isoforms. The study of mutant β holoenzymes revealed that the ATP-dependent increase in CAM affinity results in two distinct states. The phosphorylation-defective (T287.306-307A) holoenzyme resides only in the low-affinity state. CAM association is further reduced in the T287A holoenzyme relative to T287.306-307A. In the absence of ATP, the affinity of CAM for the T287.306-307A mutant and the wild-type monomer are comparable. The affinity of the ATP-binding impaired (K43R) mutant is even weaker. In ATP, the K43R holoenzyme resides in the low-affinity state. The phosphomimetic mutant (T287D) resides only in a 1000-fold higher-affinity state, with mean CAM occupancy of more than half of the 14-mer holoenzyme stoichiometry in picomolar CAM. ATP promotes T287D holoenzyme disassembly but does not elevate CAM occupancy. Single Poisson distributions characterized the ATP-dependent CAM occupancy of mutant holoenzymes. In contrast, the CAM occupancy of the wild-type population had a two-state distribution with both low- and high-affinity states represented. The low-affinity state was the dominant state, a result different from published in vitro assays. Differences in assay conditions can alter the balance between activating and inhibitory autophosphorylation. Bound ATP could be sufficient for CaMKII structural function, while antagonistic autophosphorylations may tune CaMKII kinase-regulated action-potential frequency decoding in vivo.

Dopamine D3 receptor modulates D2 receptor effects on cAMP and GABA release at striatopallidal terminals-Modulation by the Ca2+-Calmodulin-CaMKII system

Dopamine D2 receptor (D2R) is expressed in striatopallidal neurons and decreases forskolin-stimulated cyclic adenine monophosphate (cAMP) accumulation and gamma-aminobutyric acid (GABA) release. Dopamine D3 receptor (D3R) mRNA is expressed in a population of striatal D2R-expressing neurons. Also, D3R protein and binding have been reported in the neuropil of globus pallidus. We explore whether D2R and D3R colocalize in striatopallidal terminals and whether D3R modulates the D2R effect on forskolin-stimulated [3H]cAMP accumulation in pallidal synaptosomes and high K+ stimulated-[3H]GABA release in pallidal slices. Previous reports in heterologous systems indicate that calmodulin (CaM) and CaMKII modulate D2R and D3R functions; thus, we study whether this system regulates its functional interaction. D2R immunoprecipitates with CaM, and pretreatment with ophiobolin A or depolarization of synaptosomes with 15 mM of K+ decreases it. Both treatments increase the D2R inhibition of forskolin-stimulated [3H]cAMP accumulation when activated with quinpirole, indicating a negative modulation of CaM on D2R function. Quinpirole also activates D3R, potentiating D2R inhibition of cAMP accumulation in the ophiobolin A-treated synaptosomes. D2R and D3R immunoprecipitate in pallidal synaptosomes and decrease after the kainic acid striatal lesion, indicating the striatal origin of the presynaptic receptors. CaM-kinase II alfa (CaMKIIα) immunoprecipitates with D3R and increases after high K+ depolarization. In the presence of KN62, a CaMKIIα blocker, D3R potentiates D2R effects on cAMP accumulation in depolarized synaptosomes and GABA release in pallidal slices, indicating D3R function regulation by CaMKIIα. Our data indicate that D3R potentiates the D2R effect on cAMP accumulation and GABA release at pallidal terminals, an interaction regulated by the CaM-CaMKIIα system.

Non-fluorescent transient states of tyrosine as a basis for label-free protein conformation and interaction studies

The amino acids tryptophan, tyrosine, and phenylalanine have been extensively used for different label-free protein studies, based on the intensity, lifetime, wavelength and/or polarization of their emitted fluorescence. Similar to most fluorescent organic molecules, these amino acids can undergo transitions into dark meta-stable states, such as triplet and photo-radical states. On the one hand, these transitions limit the fluorescence signal, but they are also highly environment-sensitive and can offer an additional set of parameters, reflecting interactions, folding states, and immediate environments around the proteins. In this work, by analyzing the average intensity of tyrosine emission under different excitation modulations with the transient state monitoring (TRAST) technique, we explored the photo physics of tyrosine as a basis for such environment-sensitive readouts. From how the dark state transitions of tyrosine varied with excitation intensity and solvent conditions we first established a photophysical model for tyrosine. Next, we studied Calmodulin (containing two tyrosines), and how its conformation is changed upon calcium binding. From these TRAST experiments, performed with 280 nm time-modulated excitation, we show that tyrosine dark state transitions clearly change with the calmodulin conformation, and may thus represent a useful source of information for (label-free) analyses of protein conformations and interactions.

Hydrogen/Deuterium Exchange Mass Spectrometry Provides Insights into the Role of Drosophila Testis-Specific Myosin VI Light Chain AndroCaM

In Drosophila testis, myosin VI plays a special role, distinct from its motor function, by anchoring components to the unusual actin-based structures (cones) that are required for spermatid individualization. For this, the two calmodulin (CaM) light-chain molecules of myosin VI are replaced by androcam (ACaM), a related protein with 67% identity to CaM. Although ACaM has a similar bi-lobed structure to CaM, with two EF hand-type Ca2+ binding sites per lobe, only one functional Ca2+ binding site operates in the amino-terminus. To understand this light chain substitution, we used hydrogen-deuterium exchange mass spectrometry (HDX-MS) to examine dynamic changes in ACaM and CaM upon Ca2+ binding and interaction with the two CaM binding motifs of myosin VI (insert2 and IQ motif). HDX-MS reveals that binding of Ca2+ to ACaM destabilizes its N-lobe but stabilizes the entire C-lobe, whereas for CaM, Ca2+ binding induces a pattern of alternating stabilization/destabilization throughout. The conformation of this stable holo-C-lobe of ACaM seems to be a "prefigured" version of the conformation adopted by the holo-C-lobe of CaM for binding to insert2 and the IQ motif of myosin VI. Strikingly, the interaction of holo-ACaM with either peptide converts the holo-N-lobe to its Ca2+-free, more stable, form. Thus, ACaM in vivo should bind the myosin VI light chain sites in an apo-N-lobe/holo-C-lobe state that cannot fulfill the Ca2+-related functions of holo-CaM required for myosin VI motor assembly and activity. These findings indicate that inhibition of myosin VI motor activity is a precondition for transition to an anchoring function.

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.

Redundant role of OsCNGC4 and OsCNGC5 encoding cyclic nucleotide-gated channels in rice pollen germination and tube growth

In staple crops, such as rice (Oryza sativa L.), pollen plays a crucial role in seed production. However, the molecular mechanisms underlying rice pollen germination and tube growth remain underexplored. Notably, we recently uncovered the redundant expression and mutual interaction of two rice genes encoding cyclic nucleotide-gated channels (CNGCs), OsCNGC4 and OsCNGC5, in mature pollen. Building on these findings, the current study focused on clarifying the functional roles of these two genes in pollen germination and tube growth. To overcome functional redundancy, we produced gene-edited rice plants with mutations in both genes using the CRISPR-Cas9 system. The resulting homozygous OsCNGC4 and OsCNGC5 gene-edited mutants (oscngc4/5) exhibited significantly lower pollen germination rates than the wild type (WT), along with severely reduced fertility. Transcriptome analysis of the double oscngc4/5 mutant revealed downregulation of genes related to receptor kinases, transporters, and cell wall metabolism. To identify the direct regulators of OsCNGC4, which form a heterodimer with OsCNGC5, we screened a yeast two-hybrid library containing rice cDNAs from mature anthers. Subsequently, we identified two calmodulin isoforms (CaM1-1 and CaM1-2), NETWORKED 2 A (NET2A), and proline-rich extension-like receptor kinase 13 (PERK13) proteins as interactors of OsCNGC4, suggesting its roles in regulating Ca2+ channel activity and F-actin organization. Overall, our results suggest that OsCNGC4 and OsCNGC5 may play critical roles in pollen germination and elongation by regulating the Ca2+ gradient in growing pollen tubes.

The Quantitative Biotinylproteomics Studies Reveal a WInd-Related Kinase 1 (Raf-Like Kinase 36) Functioning as an Early Signaling Component in Wind-Induced Thigmomorphogenesis and Gravitropism

Wind is one of the most prevalent environmental forces entraining plants to develop various mechano-responses, collectively called thigmomorphogenesis. Largely unknown is how plants transduce these versatile wind force signals downstream to nuclear events and to the development of thigmomorphogenic phenotype or anemotropic response. To identify molecular components at the early steps of the wind force signaling, two mechanical signaling-related phosphoproteins, identified from our previous phosphoproteomic study of Arabidopsis touch response, mitogen-activated protein kinase kinase 1 (MKK1) and 2 (MKK2), were selected for performing in planta TurboID (ID)-based quantitative proximity-labeling (PL) proteomics. This quantitative biotinylproteomics was separately performed on MKK1-ID and MKK2-ID transgenic plants, respectively, using the genetically engineered TurboID biotin ligase expression transgenics as a universal control. This unique PTM proteomics successfully identified 11 and 71 MKK1 and MKK2 putative interactors, respectively. Biotin occupancy ratio (BOR) was found to be an alternative parameter to measure the extent of proximity and specificity between the proximal target proteins and the bait fusion protein. Bioinformatics analysis of these biotinylprotein data also found that TurboID biotin ligase favorably labels the loop region of target proteins. A WInd-Related Kinase 1 (WIRK1), previously known as rapidly accelerated fibrosarcoma (Raf)-like kinase 36 (RAF36), was found to be a putative common interactor for both MKK1 and MKK2 and preferentially interacts with MKK2. Further molecular biology studies of the Arabidopsis RAF36 kinase found that it plays a role in wind regulation of the touch-responsive TCH3 and CML38 gene expression and the phosphorylation of a touch-regulated PATL3 phosphoprotein. Measurement of leaf morphology and shoot gravitropic response of wirk1 (raf36) mutant revealed that the WIRK1 gene is involved in both wind-triggered rosette thigmomorphogenesis and gravitropism of Arabidopsis stems, suggesting that the WIRK1 (RAF36) protein probably functioning upstream of both MKK1 and MKK2 and that it may serve as the crosstalk point among multiple mechano-signal transduction pathways mediating both wind mechano-response and gravitropism.

Arabidopsis Calmodulin-like Proteins CML13 and CML14 Interact with Calmodulin-Binding Transcriptional Activators and Function in Salinity Stress Response

Eukaryotic cells use calcium ions (Ca2+) as second messengers, particularly in response to abiotic and biotic stresses. These signals are detected by Ca2+ sensor proteins, such as calmodulin (CaM), which regulate the downstream target proteins. Plants also possess many CaM-like proteins (CMLs), most of which remain unstudied. We recently demonstrated that Arabidopsis CML13 and CML14 interact with proteins containing isoleucine/glutamine (IQ) domains, including CaM-binding transcriptional activators (CAMTAs). Here, we show that CaM, CML13 and CML14 bind all six members of the Arabidopsis CAMTA family. Using a combination of in planta and in vitro protein-interaction assays, we tested 11 members of the CaM/CML family and demonstrated that only CaM, CML13 and CML14 bind to CAMTA IQ domains. CaM, CML13 and CML14 showed Ca2+-independent binding to the IQ region of CAMTA6 and CAMTA3, and CAMTA6 in vitro exhibited some specificity toward individual IQ domains within CAMTA6 in split-luciferase in planta assays. We show that cml13 mutants exhibited enhanced salinity tolerance during germination compared to wild-type plants, a phenotype similar to camta6 mutants. In contrast, plants overexpressing CML13-GFP or CML14-GFP in the wild-type background showed increased NaCl sensitivity. Under mannitol stress, cml13 mutants were more susceptible than camta6 mutants or wild-type plants. The phenotype of cml13 mutants could be rescued with the wild-type CML13 gene. Several salinity-marker genes under CAMTA6 control were similarly misregulated in both camta6 and cml13 mutants, further supporting a role for CML13 in CAMTA6 function. Collectively, our data suggest that CML13 and CML14 participate in abiotic stress signaling as CAMTA effectors.

Calcium- and calmodulin-dependent inhibition of NMDA receptor currents

Calcium ions (Ca2+) reduce NMDA receptor currents through several distinct mechanisms. Among these, calmodulin (CaM)-dependent inhibition (CDI) accomplishes rapid, reversible, and incomplete reduction of the NMDA receptor currents in response to elevations in intracellular Ca2+. Quantitative and mechanistic descriptions of CDI of NMDA receptor-mediated signals have been marred by variability originating, in part, from differences in the conditions and metrics used to evaluate this process across laboratories. Recent ratiometric approaches to measure the magnitude and kinetics of NMDA receptor CDI have facilitated rapid insights into this phenomenon. Notably, the kinetics and magnitude of NMDA receptor CDI depend on the degree of saturation of its CaM binding sites, which represent the bona fide calcium sensor for this type of inhibition, the kinetics and magnitude of the Ca2+ signal, which depends on the biophysical properties of the NMDA receptor or of adjacent Ca2+ sources, and on the relative distribution of Ca2+ sources and CaM molecules. Given that all these factors vary widely during development, across cell types, and with physiological and pathological states, it is important to understand how NMDA receptor CDI develops and how it contributes to signaling in the central nervous system. Here, we review briefly these recent advances and highlight remaining questions about the structural and kinetic mechanisms of NMDA receptor CDI. Given that pathologies can arise from several sources, including mutations in the NMDA receptor and in CaM, understanding how CaM responds to intracellular Ca2+ signals to initiate conformational changes in NMDA receptors, and mapping the structural domains responsible will help to envision novel therapeutic strategies to neuropsychiatric diseases, which presently have limited available treatments.

Electroacupuncture at GB20 improves cognitive ability and synaptic plasticity via the CaM-CaMKII-CREB signaling pathway following cerebral ischemia-reperfusion injury in rats

BACKGROUND

This study aimed to investigate the effects of electroacupuncture (EA) on cognitive recovery and synaptic remodeling in a rat model of middle cerebral artery occlusion (MCAO) followed by reperfusion and explore the possible mechanism.

METHOD

Focal cerebral ischemia was modeled in healthy adult Sprague-Dawley rats by MCAO. The MCAO rats were classified into four groups: sham, MCAO, MCAO + GB20 (receiving EA at GB20) and MCAO + NA (receiving EA at a "non-acupoint" location not corresponding to any traditional acupuncture point location about 10 mm above the iliac crest). Neurological deficit scores and behavior were assessed before and during the treatment. After intervention for 7 days, the hippocampus was dissected to analyze growth-associated protein (GAP)-43, synaptophysin (SYN) and postsynaptic density protein (PSD)-95 expression levels by Western blotting. Bioinformatic analysis and primary hippocampal neurons with calcium-voltage gated channel subunit alpha 1B (CACNA1B) gene overexpression were used to screen the target genes for EA against MCAO.

RESULTS

Significant amelioration of neurological deficits and learning/memory were found in MCAO + GB20 rats compared with MCAO or MCAO + NA rats. Protein levels of GAP-43, SYN and PSD-95 were significantly improved in MCAO + GB20-treated rats together with an increase in the number of synapses in the hippocampal CA1 region. CACNA1B appeared to be a target gene of EA in MCAO. There were increased mRNA levels of CACNA1B, calmodulin (CaM), Ca2+/calmodulin-dependent protein kinase type II (CaMKII) and cyclic adenosine monophosphate response element binding (CREB) and increased phosphorylation of CaM, CaMKII and CREB in the hippocampal region in MCAO + GB20 versus MCAO and MCAO + NA groups. CACNA1B overexpression modulated expression of the CaM-CaMKII-CREB axis.

CONCLUSION

EA treatment at GB20 may ameliorate the negative effects of MCAO on cognitive function in rats by enhancing synaptic plasticity. EA treatment at GB20 may exert this neuroprotective effect by regulating the CACNA1B-CaM-CaMKII-CREB axis.

Sphingosylphosphorylcholine alleviates pressure overload-induced myocardial remodeling in mice via inhibiting CaM-JNK/p38 signaling pathway

Apoptosis plays a critical role in the development of heart failure, and sphingosylphosphorylcholine (SPC) is a bioactive sphingolipid naturally occurring in blood plasma. Some studies have shown that SPC inhibits hypoxia-induced apoptosis in myofibroblasts, the crucial non-muscle cells in the heart. Calmodulin (CaM) is a known SPC receptor. In this study we investigated the role of CaM in cardiomyocyte apoptosis in heart failure and the associated signaling pathways. Pressure overload was induced in mice by trans-aortic constriction (TAC) surgery. TAC mice were administered SPC (10 μM·kg-1·d-1) for 4 weeks post-surgery. We showed that SPC administration significantly improved survival rate and cardiac hypertrophy, and inhibited cardiac fibrosis in TAC mice. In neonatal mouse cardiomyocytes, treatment with SPC (10 μM) significantly inhibited Ang II-induced cardiomyocyte hypertrophy, fibroblast-to-myofibroblast transition and cell apoptosis accompanied by reduced Bax and phosphorylation levels of CaM, JNK and p38, as well as upregulated Bcl-2, a cardiomyocyte-protective protein. Thapsigargin (TG) could enhance CaM functions by increasing Ca2+ levels in cytoplasm. TG (3 μM) annulled the protective effect of SPC against Ang II-induced cardiomyocyte apoptosis. Furthermore, we demonstrated that SPC-mediated inhibition of cardiomyocyte apoptosis involved the regulation of p38 and JNK phosphorylation, which was downstream of CaM. These results offer new evidence for SPC regulation of cardiomyocyte apoptosis, potentially providing a new therapeutic target for cardiac remodeling following stress overload.

Revealing eEF-2 kinase: recent structural insights into function

The α-kinase eukaryotic elongation factor 2 kinase (eEF-2K) regulates translational elongation by phosphorylating its ribosome-associated substrate, the GTPase eEF-2. eEF-2K is activated by calmodulin (CaM) through a distinctive mechanism unlike that in other CaM-dependent kinases (CAMK). We describe recent structural insights into this unique activation process and examine the effects of specific regulatory signals on this mechanism. We also highlight key unanswered questions to guide future structure-function studies. These include structural mechanisms which enable eEF-2K to interact with upstream/downstream partners and facilitate its integration of diverse inputs, including Ca2+ transients, phosphorylation mediated by energy/nutrient-sensing pathways, pH changes, and metabolites. Answering these questions is key to establishing how eEF-2K harmonizes translation with cellular requirements within the boundaries of its molecular landscape.

Oomycete effector AVRblb2 targets cyclic nucleotide-gated channels through calcium sensors to suppress pattern-triggered immunity

Transient and rapid increase in cytosolic Ca2+ plays a crucial role in plant-pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). Cyclic nucleotide-gated channels (CNGCs) have been implicated in mediating this Ca2+ influx; however, their regulatory mechanisms remain poorly understood. Here, we have found that AVRblb2 requires the calmodulin (CaM) and calmodulin-like (CML) proteins as co-factors to interact with the NbCNGCs, resulting in the formation of AVRblb2-CaM/CML-NbCNGCs complex. Furthermore, CaM and CML are dissociated from NbCNGC18 during PTI response to increase Ca2+ influx; however, Avrblb2 inhibits calcium channel activation by disrupting the release of CaM and CML from NbCNGC18. Following recognition of PAMP, NbCNGC18 forms active heteromeric channels with other NbCNGCs, which may give selectivity of CNGC complex against diverse signals for fine-tuning of cytosolic Ca2+ level to mediate appropriate responses. Silencing of multiple NbCNGCs compromised the function of AVRblb2 on the pathogenicity of Phytophthora infestans, confirming that AVRblb2 contributes to pathogen virulence by targeting CNGCs. Our findings provide new insights into the regulation of CNGCs in PTI and the role of pathogen effectors in manipulating host cell physiology to promote infection.

The Complex Interplay between Toxic Hallmark Proteins, Calmodulin-Binding Proteins, Ion Channels, and Receptors Involved in Calcium Dyshomeostasis in Neurodegeneration

Calcium dyshomeostasis is an early critical event in neurodegeneration as exemplified by Alzheimer's (AD), Huntington's (HD) and Parkinson's (PD) diseases. Neuronal calcium homeostasis is maintained by a diversity of ion channels, buffers, calcium-binding protein effectors, and intracellular storage in the endoplasmic reticulum, mitochondria, and lysosomes. The function of these components and compartments is impacted by the toxic hallmark proteins of AD (amyloid beta and Tau), HD (huntingtin) and PD (alpha-synuclein) as well as by interactions with downstream calcium-binding proteins, especially calmodulin. Each of the toxic hallmark proteins (amyloid beta, Tau, huntingtin, and alpha-synuclein) binds to calmodulin. Multiple channels and receptors involved in calcium homeostasis and dysregulation also bind to and are regulated by calmodulin. The primary goal of this review is to show the complexity of these interactions and how they can impact research and the search for therapies. A secondary goal is to suggest that therapeutic targets downstream from calcium dyshomeostasis may offer greater opportunities for success.

The role of phosphorylation in calmodulin-mediated gating of human AQP0

Aquaporin-0 (AQP0) is the main water channel in the mammalian lens and is involved in accommodation and maintaining lens transparency. AQP0 binds the Ca2+-sensing protein calmodulin (CaM) and this interaction is believed to gate its water permeability by closing the water-conducting pore. Here, we express recombinant and functional human AQP0 in Pichia pastoris and investigate how phosphorylation affects the interaction with CaM in vitro as well as the CaM-dependent water permeability of AQP0 in proteoliposomes. Using microscale thermophoresis and surface plasmon resonance technology we show that the introduction of the single phospho-mimicking mutations S229D and S235D in AQP0 reduces CaM binding. In contrast, CaM interacts with S231D with similar affinity as wild type, but in a different manner. Permeability studies of wild-type AQP0 showed that the water conductance was significantly reduced by CaM in a Ca2+-dependent manner, whereas AQP0 S229D, S231D and S235D were all locked in an open state, insensitive to CaM. We propose a model in which phosphorylation of AQP0 control CaM-mediated gating in two different ways (1) phosphorylation of S229 or S235 abolishes binding (the pore remains open) and (2) phosphorylation of S231 results in CaM binding without causing pore closure, the functional role of which remains to be elucidated. Our results suggest that site-dependent phosphorylation of AQP0 dynamically controls its CaM-mediated gating. Since the level of phosphorylation increases towards the lens inner cortex, AQP0 may become insensitive to CaM-dependent gating along this axis.

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.

Megalencephalic leukoencephalopathy with subcortical cysts protein-1: A new calcium-sensitive protein functionally activated by endoplasmic reticulum calcium release and calmodulin binding in astrocytes

BACKGROUND

MLC1 is a membrane protein highly expressed in brain perivascular astrocytes and whose mutations account for the rare leukodystrophy (LD) megalencephalic leukoencephalopathy with subcortical cysts disease (MLC). MLC is characterized by macrocephaly, brain edema and cysts, myelin vacuolation and astrocyte swelling which cause cognitive and motor dysfunctions and epilepsy. In cultured astrocytes, lack of functional MLC1 disturbs cell volume regulation by affecting anion channel (VRAC) currents and the consequent regulatory volume decrease (RVD) occurring in response to osmotic changes. Moreover, MLC1 represses intracellular signaling molecules (EGFR, ERK1/2, NF-kB) inducing astrocyte activation and swelling following brain insults. Nevertheless, to date, MLC1 proper function and MLC molecular pathogenesis are still elusive. We recently reported that in astrocytes MLC1 phosphorylation by the Ca2+/Calmodulin-dependent kinase II (CaMKII) in response to intracellular Ca2+ release potentiates MLC1 activation of VRAC. These results highlighted the importance of Ca2+ signaling in the regulation of MLC1 functions, prompting us to further investigate the relationships between intracellular Ca2+ and MLC1 properties.

METHODS

We used U251 astrocytoma cells stably expressing wild-type (WT) or mutated MLC1, primary mouse astrocytes and mouse brain tissue, and applied biochemistry, molecular biology, video imaging and electrophysiology techniques.

RESULTS

We revealed that WT but not mutant MLC1 oligomerization and trafficking to the astrocyte plasma membrane is favored by Ca2+ release from endoplasmic reticulum (ER) but not by capacitive Ca2+ entry in response to ER depletion. We also clarified the molecular events underlining MLC1 response to cytoplasmic Ca2+ increase, demonstrating that, following Ca2+ release, MLC1 binds the Ca2+ effector protein calmodulin (CaM) at the carboxyl terminal where a CaM binding sequence was identified. Using a CaM inhibitor and generating U251 cells expressing MLC1 with CaM binding site mutations, we found that CaM regulates MLC1 assembly, trafficking and function, being RVD and MLC-linked signaling molecules abnormally regulated in these latter cells.

CONCLUSION

Overall, we qualified MLC1 as a Ca2+ sensitive protein involved in the control of volume changes in response to ER Ca2+ release and astrocyte activation. These findings provide new insights for the comprehension of the molecular mechanisms responsible for the myelin degeneration occurring in MLC and other LD where astrocytes have a primary role in the pathological process.

Mapping interactions of calmodulin and neuronal NO synthase by crosslinking and mass spectrometry

Neuronal nitric oxide synthase (nNOS) is a homodimeric cytochrome P450-like enzyme that catalyzes the conversion of L-arginine to nitric oxide in the presence of NADPH and molecular oxygen. The binding of calmodulin (CaM) to a linker region between the FAD/FMN-containing reductase domain, and the heme-containing oxygenase domain is needed for electron transfer reactions, reduction of the heme, and NO synthesis. Due to the dynamic nature of the reductase domain and low resolution of available full-length structures, the exact conformation of the CaM-bound active complex during heme reduction is still unresolved. Interestingly, hydrogen-deuterium exchange and mass spectrometry studies revealed interactions of the FMN domain and CaM with the oxygenase domain for iNOS, but not nNOS. This finding prompted us to utilize covalent crosslinking and mass spectrometry to clarify interactions of CaM with nNOS. Specifically, MS-cleavable bifunctional crosslinker disuccinimidyl dibutyric urea was used to identify thirteen unique crosslinks between CaM and nNOS as well as 61 crosslinks within the nNOS. The crosslinks provided evidence for CaM interaction with the oxygenase and reductase domain residues as well as interactions of the FMN domain with the oxygenase dimer. Cryo-EM studies, which gave a high-resolution model of the oxygenase domain, along with crosslink-guided docking provided a model of nNOS that brings the FMN within 15 Å of the heme in support for a more compact conformation than previously observed. These studies also point to the utility of covalent crosslinking and mass spectrometry in capturing transient dynamic conformations that may not be captured by hydrogen-deuterium exchange and mass spectrometry experiments.

ATP-mediated increase in H+ efflux from retinal Müller cells of the axolotl

Previous work has shown that activation of tiger salamander retinal radial glial cells by extracellular ATP induces a pronounced extracellular acidification, which has been proposed to be a potent modulator of neurotransmitter release. This study demonstrates that low micromolar concentrations of extracellular ATP similarly induce significant H+ effluxes from Müller cells isolated from the axolotl retina. Müller cells were enzymatically isolated from axolotl retina and H+ fluxes were measured from individual cells using self-referencing H+-selective microelectrodes. The increased H+ efflux from axolotl Müller cells induced by extracellular ATP required activation of metabotropic purinergic receptors and was dependent upon calcium released from internal stores. We further found that the ATP-evoked increase in H+ efflux from Müller cells of both tiger salamander and axolotl were sensitive to pharmacological agents known to interrupt calmodulin and protein kinase C (PKC) activity: chlorpromazine (CLP), trifluoperazine (TFP), and W-7 (all calmodulin inhibitors) and chelerythrine, a PKC inhibitor, all attenuated ATP-elicited increases in H+ efflux. ATP-initiated H+ fluxes of axolotl Müller cells were also significantly reduced by amiloride, suggesting a significant contribution by sodium-hydrogen exchangers (NHEs). In addition, α-cyano-4-hydroxycinnamate (4-cin), a monocarboxylate transport (MCT) inhibitor, also reduced the ATP-induced increase in H+ efflux in both axolotl and tiger salamander Müller cells, and when combined with amiloride, abolished ATP-evoked increase in H+ efflux. These data suggest that axolotl Müller cells are likely to be an excellent model system to understand the cell-signaling pathways regulating H+ release from glia and the role this may play in modulating neuronal signaling.NEW & NOTEWORTHY Glial cells are a key structural part of the tripartite synapse and have been suggested to regulate synaptic transmission, but the regulatory mechanisms remain unclear. We show that extracellular ATP, a potent glial cell activator, induces H+ efflux from axolotl retinal Müller (glial) cells through a calcium-dependent pathway that is likely to involve calmodulin, PKC, Na+/H+ exchange, and monocarboxylate transport, and suggest that such H+ release may play a key role in modulating neuronal transmission.

Hypothesis paper: the development of a regulatory layer in P2B autoinhibited Ca2+-ATPases may have facilitated plant terrestrialization and animal multicellularization

With the appearance of plants and animals, new challenges emerged. These multicellular eukaryotes had to solve for example the difficulties of multifaceted communication between cells and adaptation to new habitats. In this paper, we are looking for one piece of the puzzle that made the development of complex multicellular eukaryotes possible with a focus on regulation of P2B autoinhibited Ca²⁺-ATPases. P2B ATPases pump Ca²⁺ out of the cytosol at the expense of ATP hydrolysis, and thereby maintain a steep gradient between the extra- and intracytosolic compartments which is utilized for Ca²⁺-mediated rapid cell signaling. The activity of these enzymes is regulated by a calmodulin (CaM)-responsive autoinhibitory region, which can be located in either termini of the protein, at the C-terminus in animals and at the N-terminus in plants. When the cytoplasmic Ca²⁺ level reaches a threshold, the CaM/Ca²⁺ complex binds to a calmodulin-binding domain (CaMBD) in the autoinhibitor, which leads to the upregulation of pump activity. In animals, protein activity is also controlled by acidic phospholipids that bind to a cytosolic portion of the pump. Here, we analyze the appearance of CaMBDs and the phospholipid-activating sequence and show that their evolution in animals and plants was independent. Furthermore, we hypothesize that different causes may have initiated the appearance of these regulatory layers: in animals, it is linked to the appearance of multicellularity, while in plants it co-occurs with their water-to-land transition.

Molecular Insights into the MLCK Activation by CaM

Calmodulin (CaM) is a universal regulatory protein that modulates numerous cellular processes by using calcium (Ca2+) as the signal. In smooth muscle cells (SMC), one major target of CaM is myosin light chain kinase (MLCK), a kinase that phosphorylates the myosin regulatory light chain and thereby regulates cell contraction. In the absence of CaM, MLCK remains inhibited by its autoinhibitory domain (AID). While it is well established that CaM activates MLCK, the molecular interactions between these two proteins remain elusive due to the lack of structural data. In this work, we constructed a molecular model of mammalian CaM (mCaM) in complex with MLCK leveraging AlphaFold, published biochemical data, and protein-protein docking. The model, along with a strategic set of CaM mutants including a inhibitory variant soybean CaM isoform 4 (sCaM-4), was subject to molecular dynamics (MD) simulations. Using principal component analysis (PCA), we mapped out the transition path for the removal of the AID from the MLCK kinase domain to provide molecular basis of MLCK activation. Additionally, we established MLCK conformations that correspond to the active and inactive states of the kinase. We showed that mCaM and sCaM-4 cause MLCK to undergo the transition to the active and inactive states, respectively. Using two structural metrics, we computed the probabilities of MLCK activation by different CaM variants, which were in good agreement with the experimental data. Distributions along these metrics revealed that different inhibitory CaM variants impair MLCK activation through unique mechanisms. We finally identified molecular contacts that contribute to the MLCK activation by CaM. Overall, we report a de novo molecular model of CaM-MLCK that provides insights into the molecular mechanism of MLCK activation by CaM. The mechanism requires effective removal of the AID while preserving an active configuration of the kinase domain. This mechanism may be shared by other MLCK isoforms and potentially other structurally similar kinases with CaM-mediated regulatory domains.

Ca2+ Signaling and Src Functions in Tumor Cells

Signaling by calcium ion (Ca2+) plays a prominent role in cell physiology, and these mechanisms are frequently altered in tumor cells. In this review, we consider the interplay of Ca2+ signaling and the functions of the proto-oncogene non-receptor tyrosine kinase c-Src in tumor cells, and the viral oncogenic variant v-Src in transformed cells. Also, other members of the Src-family kinases are considered in this context. The role of Ca2+ in the cell is frequently mediated by Ca2+-binding proteins, where the Ca2+-sensor protein calmodulin (CaM) plays a prominent, essential role in many cellular signaling pathways. Thus, we cover the available information on the role and direct interaction of CaM with c-Src and v-Src in cancerous cells, the phosphorylation of CaM by v-Src/c-Src, and the actions of different CaM-regulated Ser/Thr-protein kinases and the CaM-dependent phosphatase calcineurin on v-Src/c-Src. Finally, we mention some clinical implications of these systems to identify mechanisms that could be targeted for the therapeutic treatment of human cancers.

Role of Phosphodiesterase 1 in the Regulation of Real-Time cGMP Levels and Contractility in Adult Mouse Cardiomyocytes

In mouse cardiomyocytes, the expression of two subfamilies of the calcium/calmodulin-regulated cyclic nucleotide phosphodiesterase 1 (PDE1)-PDE1A and PDE1C-has been reported. PDE1C was found to be the major subfamily in the human heart. It is a dual substrate PDE and can hydrolyze both 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP). Previously, it has been reported that the PDE1 inhibitor ITI-214 shows positive inotropic effects in heart failure patients which were largely attributed to the cAMP-dependent protein kinase (PKA) signaling. However, the role of PDE1 in the regulation of cardiac cGMP has not been directly addressed. Here, we studied the effect of PDE1 inhibition on cGMP levels in adult mouse ventricular cardiomyocytes using a highly sensitive fluorescent biosensor based on Förster resonance energy transfer (FRET). Live-cell imaging in paced and resting cardiomyocytes showed an increase in cGMP after PDE1 inhibition with ITI-214. Furthermore, PDE1 inhibition and PDE1A knockdown amplified the cGMP-FRET responses to the nitric oxide (NO)-donor sodium nitroprusside (SNP) but not to the C-type natriuretic peptide (CNP), indicating a specific role of PDE1 in the regulation of the NO-sensitive guanylyl cyclase (NO-GC)-regulated cGMP microdomain. ITI-214, in combination with CNP or SNP, showed a positive lusitropic effect, improving the relaxation of isolated myocytes. Immunoblot analysis revealed increased phospholamban (PLN) phosphorylation at Ser-16 in cells treated with a combination of SNP and PDE1 inhibitor but not with SNP alone. Our findings reveal a previously unreported role of PDE1 in the regulation of the NO-GC/cGMP microdomain and mouse ventricular myocyte contractility. Since PDE1 serves as a cGMP degrading PDE in cardiomyocytes and has the highest hydrolytic activities, it can be expected that PDE1 inhibition might be beneficial in combination with cGMP-elevating drugs for the treatment of cardiac diseases.

Calmodulin and calmodulin-like protein-mediated plant responses to biotic stresses

Plants have evolved a set of finely regulated mechanisms to respond to various biotic stresses. Transient changes in intracellular calcium (Ca2+ ) concentration have been well documented to act as cellular signals in coupling environmental stimuli to appropriate physiological responses with astonishing accuracy and specificity in plants. Calmodulins (CaMs) and calmodulin-like proteins (CMLs) are extensively characterized as important classes of Ca2+ sensors. The spatial-temporal coordination between Ca2+ transients, CaMs/CMLs and their target proteins is critical for plant responses to environmental stresses. Ca2+ -loaded CaMs/CMLs interact with and regulate a broad spectrum of target proteins, such as ion transporters (including channels, pumps, and antiporters), transcription factors, protein kinases, protein phosphatases, metabolic enzymes and proteins with unknown biological functions. This review focuses on mechanisms underlying how CaMs/CMLs are involved in the regulation of plant responses to diverse biotic stresses including pathogen infections and herbivore attacks. Recent discoveries of crucial functions of CaMs/CMLs and their target proteins in biotic stress resistance revealed through physiological, molecular, biochemical, and genetic analyses have been described, and intriguing insights into the CaM/CML-mediated regulatory network are proposed. Perspectives for future directions in understanding CaM/CML-mediated signalling pathways in plant responses to biotic stresses are discussed. The application of accumulated knowledge of CaM/CML-mediated signalling in biotic stress responses into crop cultivation would improve crop resistance to various biotic stresses and safeguard our food production in the future.

FAM71D is dispensable for spermatogenesis and male fertility in mice

In mammals, the generation of sperm cells capable of fertilization is a highly complex process including spermatogenesis in the testis and maturation in the epididymis. In our previous study, we have demonstrated that FAM71D (Family with sequence similarity 71, member D), which could interact with calmodulin, was highly expressed in human and mouse testis. To investigate the physiological role of FAM71D in spermatogenesis, we next generate Fam71d loss-of-function mouse model using CRISPR/Cas9 technology. We performed immunofluorescence and RT-qPCR to examine the protein and mRNA expression in testicular cells. We found that FAM71D was predominantly localized in the round and elongated spermatids. And FAM71D KO mice displayed normal development of germ cell and fertility. Furthermore, testicular histology and sperm concentration showed no significant difference between WT and KO mice. These data demonstrate that FAM71D is dispensable for mouse spermatogenesis and male fertility.

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.

Downregulated calmodulin expression contributes to endothelial cell impairment in diabetes

Endothelial dysfunction, a central hallmark of cardiovascular pathogenesis in diabetes mellitus, is characterized by impaired endothelial nitric oxide synthase (eNOS) and NO bioavailability. However, the underlying mechanisms remain unclear. Here in this study, we aimed to identify the role of calmodulin (CaM) in diabetic eNOS dysfunction. Human umbilical vein endothelial cells and murine endothelial progenitor cells (EPCs) treated with high glucose (HG) exhibited downregulated CaM mRNA/protein and vascular endothelial growth factor (VEGF) expression with impeded eNOS phosphorylation and cell migration/tube formation. These perturbations were reduplicated in CALM1-knockdown cells but prevented in CALM1-overexpressing cells. EPCs from type 2 diabetes animals behaved similarly to HG-treated normal EPCs, which could be rescued by CALM1-gene transduction. Consistently, diabetic animals displayed impaired eNOS phosphorylation, endothelium-dependent dilation, and CaM expression in the aorta, as well as deficient physical interaction of CaM and eNOS in the gastrocnemius. Local CALM1 gene delivery into a diabetic mouse ischemic hindlimb improved the blunted limb blood perfusion and gastrocnemius angiogenesis, and foot injuries. Diabetic patients showed insufficient foot microvascular autoregulation, eNOS phosphorylation, and NO production with downregulated CaM expression in the arterial endothelium, and abnormal CALM1 transcription in genome-wide sequencing analysis. Therefore, our findings demonstrated that downregulated CaM expression is responsible for endothelium dysfunction and angiogenesis impairment in diabetes, and provided a novel mechanism and target to protect against diabetic endothelial injury.

Calmodulin regulates protease versus co-chaperone activity of a metacaspase

Metacaspases are ancestral homologs of caspases that can either promote cell death or confer cytoprotection. Furthermore, yeast (Saccharomyces cerevisiae) metacaspase Mca1 possesses dual biochemical activity: proteolytic activity causing cell death and cytoprotective, co-chaperone-like activity retarding replicative aging. The molecular mechanism favoring one activity of Mca1 over another remains elusive. Here, we show that this mechanism involves calmodulin binding to the N-terminal pro-domain of Mca1, which prevents its proteolytic activation and promotes co-chaperone-like activity, thus switching from pro-cell death to anti-aging function. The longevity-promoting effect of Mca1 requires the Hsp40 co-chaperone Sis1, which is necessary for Mca1 recruitment to protein aggregates and their clearance. In contrast, proteolytically active Mca1 cleaves Sis1 both in vitro and in vivo, further clarifying molecular mechanism behind a dual role of Mca1 as a cell-death protease versus gerontogene.

Calmodulin-Targeting Molecules from Ageratina grandifolia

Four new natural chemical entities, including 2-hydroxy-α-truxillic acid (2), (3R,4S)-2,2-dimethyl-3-hydroxy-4-(1-angeloyloxy)-6-acetyl-7-methoxychromane (3), N-tricosanoyltyramine (4), and grandifolamide (5), were isolated along with 11 known compounds (1, 6-15) from the aerial parts of Ageratina grandifolia. The chemical structures were elucidated using chemical derivatization and HR-MS, NMR, and DFT-calculated chemical shifts, combined with DP4+ statistical analysis. It was found that 2 decomposed into its biogenetic precursor, o-coumaric acid, upon standing at room temperature for a few weeks. 3,5-Diprenyl-4-hydroxyacetophenone (8), O-methylencecalinol (10), encecalin (11), and encecalinol (12) bound to calmodulin (CaM) with higher affinity than chlorpromazine, a well-known CaM inhibitor. Molecular dynamics studies revealed that the complexes of these compounds with CaM remained stable during the simulation. Altogether these results revealed the therapeutic and research tool potential of compounds 8, 10, 11, and 12.

Calmodulinopathy in Japanese Children - Their Cardiac Phenotypes Are Severe and Show Early Onset in Fetal Life and Infancy

BACKGROUND

Cardiac calmodulinopathy, characterized by a life-threatening arrhythmia and sudden death in the young, is extremely rare and caused by genes encoding calmodulin, namely calmodulin 1 (CALM1), CALM2, and CALM3.Methods and Results: We screened 195 symptomatic children (age 0-12 years) who were suspected of inherited arrhythmias for 48 candidate genes, using a next-generation sequencer. Ten probands were identified as carrying variants in any of CALM1-3 (5%; median age 5 years), who were initially diagnosed with long QT syndrome (LQTS; n=5), catecholaminergic polymorphic ventricular tachycardia (CPVT; n=3), and overlap syndrome (n=2). Two probands harbored a CALM1 variant and 8 probands harbored 6 CALM2 variants. There were 4 clinical phenotypes: (1) documented lethal arrhythmic events (LAEs): 4 carriers of N98S in CALM1 or CALM2; (2) suspected LAEs: CALM2 p.D96G and D132G carriers experienced syncope and transient cardiopulmonary arrest under emotional stimulation; (3) critical cardiac complication: CALM2 p.D96V and p.E141K carriers showed severe cardiac dysfunction with QTc prolongation; and (4) neurological and developmental disorders: 2 carriers of CALM2 p.E46K showed cardiac phenotypes of CPVT. Beta-blocker therapy was effective in all cases except cardiac dysfunction, especially in combination with flecainide (CPVT-like phenotype) and mexiletine (LQTS-like).

CONCLUSIONS

Calmodulinopathy patients presented severe cardiac features, and their onset of LAEs was earlier in life, requiring diagnosis and treatment at the earliest age possible.

Osteoblast-lineage calcium/calmodulin-dependent kinase 2 delta and gamma regulates bone mass and quality

Bone regulates its mass and quality in response to diverse mechanical, hormonal, and local signals. The bone anabolic or catabolic responses to these signals are often received by osteocytes, which then coordinate the activity of osteoblasts and osteoclasts on bone surfaces. We previously established that calcium/calmodulin-dependent kinase 2 (CaMKII) is required for osteocytes to respond to some bone anabolic cues in vitro. However, a role for CaMKII in bone physiology in vivo is largely undescribed. Here, we show that conditional codeletion of the most abundant isoforms of CaMKII (delta and gamma) in mature osteoblasts and osteocytes [Ocn-cre:Camk2d/Camk2g double-knockout (dCKO)] caused severe osteopenia in both cortical and trabecular compartments by 8 wk of age. In addition to having less bone mass, dCKO bones are of worse quality, with significant deficits in mechanical properties, and a propensity to fracture. This striking skeletal phenotype is multifactorial, including diminished osteoblast activity, increased osteoclast activity, and altered phosphate homeostasis both systemically and locally. These dCKO mice exhibited decreased circulating phosphate (hypophosphatemia) and increased expression of the phosphate-regulating hormone fibroblast growth factor 23. Additionally, dCKO mice expressed less bone-derived tissue nonspecific alkaline phosphatase protein than control mice. Consistent with altered phosphate homeostasis, we observed that dCKO bones were hypo-mineralized with prominent osteoid seams, analogous to the phenotypes of mice with hypophosphatemia. Altogether, these data reveal a fundamental role for osteocyte CaMKIIδ and CaMKIIγ in the maintenance of bone mass and bone quality and link osteoblast/osteocyte CaMKII to phosphate homeostasis.

Anti-inflammatory activity of calmodulin-lysine N-methyltransferase through suppressing the caspase-11 non-canonical inflammasome

Calmodulin (CaM)-lysine N-methyltransferase (CAMKMT) is a novel methyltransferase that catalyzes lysine trimethylation in CaM. However, its specific roles in inflammatory responses and diseases remain unclear. In this study, we investigated the effects of CAMKMT on caspase-11 non-canonical inflammasomes. CAMKMT expression levels were significantly decreased during inflammatory responses activated by caspase-11 non-canonical inflammasome in macrophages. Moreover, CaM lysine trimethylation was markedly inhibited, but no change was observed in CaM expression during these inflammatory responses in macrophages. Activation of the CaM downstream effectors, CaM-dependent proteinkinase kinase 2 and CaM-dependent proteinkinase type IV, was also inhibited during inflammatory responses activated by caspase-11 non-canonical inflammasome in macrophages. Notably, forced expression of CAMKMT restrained caspase-11 non-canonical inflammasome activation via inhibiting proteolytic activation of caspase-11 and gasdermin D (GSDMD), which in turn suppressed pyroptosis and the release of interleukin (IL)-1β and IL-18 in macrophages. Finally, an in vivo study revealed that CAMKMT ameliorated lipopolysaccharide (LPS)-stimulated acute lethal sepsis in mice by increasing the survival rate and reducing the serum levels of IL-1 β. These findings suggest CAMKMT as a novel methyltransferase that plays an anti-inflammatory role through restraining caspase-11 non-canonical inflammasome in macrophages.

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.

The Ca2+/Calmodulin-dependent Calcineurin/NFAT Signaling Pathway in the Pathogenesis of Insulin Resistance in Skeletal Muscle

Skeletal muscle is the tissue directly involved in insulin-stimulated glucose uptake. Glucose is the primary energy substrate for contracting muscles, and proper metabolism of glucose is essential for health. Contractile activity and the associated Ca2+signaling regulate functional capacity and muscle mass. A high concentration of Ca2+and the presence of calmodulin (CaM) leads to the activation of calcineurin (CaN), a protein with serine-threonine phosphatase activity. The signaling pathway linked with CaN and transcription factors like the nuclear factor of activated T cells (NFAT) is essential for skeletal muscle development and reprogramming of fast-twitch to slow-twitch fibers. CaN activation may promote metabolic adaptations in muscle cells, resulting in better insulin-stimulated glucose transport. The molecular mechanisms underlying the altered insulin response remain unclear. The role of the CaN/NFAT pathway in regulating skeletal muscle hypertrophy is better described than its involvement in the pathogenesis of insulin resistance. Thus, there are opportunities for future research in that field. This review presents the role of CaN/NFAT signaling and suggests the relationship with insulin-resistant muscles.

Comprehensive comparative assessment of the Arabidopsis thaliana MLO2-CALMODULIN2 interaction by various in vitro and in vivo protein-protein interaction assays

Mildew resistance locus o (MLO) proteins are heptahelical integral membrane proteins of which some isoforms act as susceptibility factors for the powdery mildew pathogen. In many angiosperm plant species, loss-of-function mlo mutants confer durable broad-spectrum resistance against the fungal disease. Barley Mlo is known to interact via a cytosolic carboxyl-terminal domain with the intracellular calcium sensor calmodulin (CAM) in a calcium-dependent manner. Site-directed mutagenesis has revealed key amino acid residues in the barley Mlo calmodulin-binding domain (CAMBD) that, when mutated, affect the MLO-CAM association. We here tested the respective interaction between Arabidopsis thaliana MLO2 and CAM2 using seven different types of in vitro and in vivo protein-protein interaction assays. In each assay, we deployed a wild-type version of either the MLO2 carboxyl terminus (MLO2CT), harboring the CAMBD, or the MLO2 full-length protein and corresponding mutant variants in which two key residues within the CAMBD were substituted by non-functional amino acids. We focused in particular on the substitution of two hydrophobic amino acids (LW/RR mutant) and found in most protein-protein interaction experiments reduced binding of CAM2 to the corresponding MLO2/MLO2CT-LW/RR mutant variants in comparison with the respective wild-type versions. However, the Ura3-based yeast split-ubiquitin system and in planta bimolecular fluorescence complementation (BiFC) assays failed to indicate reduced CAM2 binding to the mutated CAMBD. Our data shed further light on the interaction of MLO and CAM proteins and provide a comprehensive comparative assessment of different types of protein-protein interaction assays with wild-type and mutant versions of an integral membrane protein.

Direct binding of calmodulin to the cytosolic C-terminal regions of sweet/umami taste receptors

Sweet and umami taste receptors recognize chemicals such as sugars and amino acids on their extracellular side and transmit signals into the cytosol of the taste cell. In contrast to ligands that act on the extracellular side of these receptors, little is known regarding the molecules that regulate receptor functions within the cytosol. In this study, we analysed the interaction between sweet and umami taste receptors and calmodulin, a representative Ca2+-dependent cytosolic regulatory protein. High prediction scores for calmodulin binding were observed on the C-terminal cytosolic side of mouse taste receptor type 1 subunit 3 (T1r3), a subunit that is common to both sweet and umami taste receptors. Pull-down assay and surface plasmon resonance analyses showed different affinities of calmodulin to the C-terminal tails of distinct T1r subtypes. Furthermore, we found that T1r3 and T1r2 showed the highest and considerable binding to calmodulin, whereas T1r1 showed weaker binding affinity. Finally, the binding of calmodulin to T1rs was consistently higher in the presence of Ca2+ than in its absence. The results suggested a possibility of the Ca2+-dependent feedback regulation process of sweet and umami taste receptor signaling by calmodulin.

Involvement of the Calmodulin-like Protein Gene VaCML92 in Grapevine Abiotic Stress Response and Stilbene Production

Calmodulin-like proteins (CMLs) are an important family of plant calcium sensor proteins that sense and decode changes in the intracellular calcium concentration in response to environmental and developmental stimuli. Nonetheless, the specific functions of individual CML family members remain largely unknown. This study aims to explore the role of the Vitis amurensis VaCML92 gene in the development of its high stress resistance and the production of stilbenes. The expression of VaCML92 was sharply induced in V. amurensis cuttings after cold stress. The VaCML92 gene was cloned and its role in the abiotic stress responses and stilbene production in grapevine was further investigated. The VaCML92-overexpressing callus cell cultures of V. amurensis and soil-grown plants of Arabidopsis thaliana exhibited enhanced tolerance to cold stress and, to a lesser extent, to the drought, while their tolerance to heat stress and high salinity was not affected. In addition, the overexpression of VaCML92 increased stilbene production in the V. amurensis cell cultures by 7.8-8.7-fold. Taken together, the data indicate that the VaCML92 gene is involved as a strong positive regulator in the rapid response to cold stress, the induction of cold stress resistance and in stilbene production in wild grapevine.

Arrhythmia-Associated Calmodulin E105A Mutation Alters the Binding Affinity of CaM to a Ryanodine Receptor 2 CaM-Binding Pocket

Calmodulin (CaM) is a small, multifunctional calcium (Ca2+)-binding sensor that binds and regulates the open probability of cardiac ryanodine receptor 2 (RyR2) at both low and high cytosolic Ca2+ concentrations. Recent isothermal titration calorimetry (ITC) studies of a number of peptides that correspond to different regions of human RyR2 showed that two regions of human RyR2 (3584-3602aa and 4255-4271aa) bind with high affinity to CaM, suggesting that these two regions might contribute to a putative RyR2 intra-subunit CaM-binding pocket. Moreover, a previously characterized de novo long QT syndrome (LQTS)-associated missense CaM mutation (E105A) which was identified in a 6-year-old boy, who experienced an aborted first episode of cardiac arrest revealed that this mutation dysregulates normal cardiac function in zebrafish by a complex mechanism that involves alterations in both CaM-Ca2+ and CaM-RyR2 interactions. Herein, to gain further insight into how the CaM E105A mutation leads to severe cardiac arrhythmia, we generated large quantities of recombinant CaMWT and CaME105A proteins. We then performed ITC experiments to investigate and compare the interactions of CaMWT and CaME105A mutant protein with two synthetic peptides that correspond to the two aforementioned human RyR2 regions, which we have proposed to contribute to the RyR2 CaM-binding pocket. Our data reveal that the E105A mutation has a significant negative effect on the interaction of CaM with both RyR2 regions in the presence and absence of Ca2+, highlighting the potential contribution of these two human RyR2 regions to an RyR2 CaM-binding pocket, which may be essential for physiological CaM/RyR2 association and thus channel regulation.

Interaction of Calmodulin with TRPM: An Initiator of Channel Modulation

Transient receptor potential melastatin (TRPM) channels, a subfamily of the TRP superfamily, constitute a diverse group of ion channels involved in mediating crucial cellular processes like calcium homeostasis. These channels exhibit complex regulation, and one of the key regulatory mechanisms involves their interaction with calmodulin (CaM), a cytosol ubiquitous calcium-binding protein. The association between TRPM channels and CaM relies on the presence of specific CaM-binding domains in the channel structure. Upon CaM binding, the channel undergoes direct and/or allosteric structural changes and triggers down- or up-stream signaling pathways. According to current knowledge, ion channel members TRPM2, TRPM3, TRPM4, and TRPM6 are directly modulated by CaM, resulting in their activation or inhibition. This review specifically focuses on the interplay between TRPM channels and CaM and summarizes the current known effects of CaM interactions and modulations on TRPM channels in cellular physiology.

Molecular regulatory mechanism of human myosin-7a

Myosin-7a is an actin-based motor protein essential for vision and hearing. Mutations of myosin-7a cause type 1 Usher syndrome, the most common and severe form of deafblindness in humans. The molecular mechanisms that govern its mechanochemistry remain poorly understood, primarily because of the difficulty of purifying stable intact protein. Here, we recombinantly produce the complete human myosin-7a holoenzyme in insect cells and characterize its biochemical and motile properties. Unlike the Drosophila ortholog that primarily associates with calmodulin (CaM), we found that human myosin-7a utilizes a unique combination of light chains including regulatory light chain, CaM, and CaM-like protein 4. Our results further reveal that CaM-like protein 4 does not function as a Ca2+ sensor but plays a crucial role in maintaining the lever arm's structural-functional integrity. Using our recombinant protein system, we purified two myosin-7a splicing isoforms that have been shown to be differentially expressed along the cochlear tonotopic axis. We show that they possess distinct mechanoenzymatic properties despite differing by only 11 amino acids at their N termini. Using single-molecule in vitro motility assays, we demonstrate that human myosin-7a exists as an autoinhibited monomer and can move processively along actin when artificially dimerized or bound to cargo adaptor proteins. These results suggest that myosin-7a can serve multiple roles in sensory systems such as acting as a transporter or an anchor/force sensor. Furthermore, our research highlights that human myosin-7a has evolved unique regulatory elements that enable precise tuning of its mechanical properties suitable for mammalian auditory functions.

Understanding the mechanism of pathogenicity through interactome studies between Arachis hypogaea L. and Aspergillus flavus

Aspergillus flavus (A. flavus) infects the peanut seeds during pre-and post-harvest stages, causing seed quality destruction for humans and livestock consumption. Even though many resistant varieties were developed, the molecular mechanism of defense interactions of peanut against A. flavus still needs further investigation. Hence, an interologous host-pathogen protein interaction (HPPI) network was constructed to understand the subcellular level interaction mechanism between peanut and A. flavus. Out of the top 10 hub proteins of both organisms, protein phosphatase 2C and cyclic nucleotide-binding/kinase domain-containing protein and different ribosomal proteins were identified as candidate proteins involved in defense. Functional annotation and subcellular localization based characterization of HPPI identified protein SGT1 homolog, calmodulin and Rac-like GTP-binding proteins to be involved in defense response against fungus. The relevance of HPPI in infectious conditions was assessed using two transcriptome data which identified the interplay of host kinase class R proteins, bHLH TFs and cell wall related proteins to impart resistance against pathogen infection. Further, the pathogenicity analysis identified glycogen phosphorylase and molecular chaperone and allergen Mod-E/Hsp90/Hsp1 as potential pathogen targets to enhance the host defense mechanism. Hence, the computationally predicted host-pathogen PPI network could provide valuable support for molecular biology experiments to understand the host-pathogen interaction. SIGNIFICANCE: Protein-protein interactions execute significant cellular interactions in an organism and are influenced majorly by stress conditions. Here we reported the host-pathogen protein-protein interaction between peanut and A. flavus, and a detailed network analysis based on function, subcellular localization, gene co-expression, and pathogenicity was performed. The network analysis identified key proteins such as host kinase class R proteins, calmodulin, SGT1 homolog, Rac-like GTP-binding proteins bHLH TFs and cell wall related to impart resistance against pathogen infection. We observed the interplay of defense related proteins and cell wall related proteins predominantly, which could be subjected to further studies. The network analysis described in this study could be applied to understand other host-pathogen systems generally.

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.