Neuronal Calcium Sensor Family Research Articles

Conformational Structural Alteration of NCS1 Protein Through Pb2+and Mn2+ Association

NCS1 (Frequenin) is a member of neuronal calcium sensor (NCS) family. This globular protein contains four EF-hand motifs and an amino-terminal myristylation sequence. Pb2+has been widely viewed as a health concern for its anthropogenic toxicity. It has been observed that Pb2+ modulates interactions between calcium-binding protein calmodulin (CaM) and its binding partners through binding in the EF-hands of CaM and it may play a significant role in Pb2+-induced neurotoxicity. Mn is a highly abundant metal in nature which has been found in human brain and associated with the several diseases like multiple sclerosis, Alzheimer's and Parkinson's disease and is considered as potential toxic element. Previous studies from our group showed Pb2+ and Cd2+ binding to DREAM protein that can contribute to Pb2+/Cd2+ induced neurotoxicity. Here we showed that Pb2+ binds to EF-hands in apo-NCS1with a high affinity (Kd = 7.0±1.5 nM) whereas Cd2+ did not show any binding with NCS1. For the first time we investigated the Mn2+ association to NCS1 protein. This cation binds with an apparent equilibrium dissociation constant of 340±67 µM. Pb2+ and Mn2+binding trigger secondary and tertiary structural rearrangements of NCS1 that are analogous to those observed for Ca2+ association. In addition, Pb2+ as well as Mn2+ promote NCS1 interaction with hydrophobic molecule 1,8-ANS. Interestingly,Ca2+NCS1:1,8-ANS complex exhibits a co-operative binding of Pb2+ with Kd = 103±23 µM whereas Mn2+ showed apparent Kd value 924±185 µM with Ca2+NCS1:1,8-ANS complex. These results suggest allosteric interactions between the 1,8-ANS binding site and Pb2+ binding EF-hands. Data provided here points towards ability of EF-hands in NCS-1 to interact with various metals and a possible role of NCS1 in Pb2+/Mn2+ neurotoxicity.

EF-hands in Neuronal Calcium Sensor Downstream Regulatory Element Antagonist Modulator Demonstrate Submillimolar Affinity for Li+: A New Prospect for Li+ Therapy.

Lithium has been used for the treatment of mood disorders for decades though the molecular mechanism of its therapeutic action and intracellular targets remain furtive. We report that neurotropic agent Li+ binds to the neuronal calcium sensor, Downstream Regulatory Element Antagonist Modulator (DREAM), with an equilibrium dissociation constant of 34 ± 4 μM and impacts DREAM structural and dynamic properties in a similar manner as observed for its physiological ligand, Ca2+. Results of fluorescence spectroscopy and molecular dynamics are consistent with Li+ binding at EF-hands. In the Li+ bound form, DREAM association to peptides mimicking DREAM binding sites in a voltage-gated potassium channel is enhanced compared to the apoprotein, whereas DREAM affinity for the presenilin binding site, helix-9, is impeded. These results suggest that DREAM and possibly other members of the neuronal calcium sensor family belong to Li+ intracellular targets and interactions between Li+ and NCS provide a molecular basis for Li+ neuroprotective action.

Cadmium association with DREAM promotes DREAM interactions with intracellular partners in a similar manner to its physiological ligand, calcium.

Cd2+ exposure has been associated with neurodegenerative diseases and other pathologies, but the underlying mechanism through which it exerts toxic effects remain unresolved. Using calorimetric and spectroscopic techniques, we show that Cd2+ binds to EF-hands in DREAM (downstream regulatory element antagonist modulator) with an equilibrium dissociation constant of 89 ± 10 nM, which is superior to that determined for Ca2+ (Kd = 1000 nM). Analogous to Ca2+ binding, Cd2+ binding triggers changes in the protein secondary and tertiary structure, including increased exposure of the hydrophobic cavities, as determined using a fluorescent probe, 1-anilinonaphthalene-8-sulfonic acid. In addition, we demonstrate that Cd2+ binding modulates DREAM interactions with FITC-labeled peptides that mimic binding sites of DREAM effector proteins; helix-9 of presenilin-1, and site-1 and site 2 of potassium voltage channel 4.3 (residues 2-22 and 70-90, respectively). Cd2+ association with DREAM increases its affinity for helix 9 of presenilin roughly 30-times compared to metal-free DREAM. The DREAM affinity for site-1 and site 2 is elevated approximately 7 and 15 times, respectively, in the presence of Cd2+. The above results suggest that DREAM and probably other members of the neuronal calcium sensor family bind Cd2+ with an affinity that is superior to that for Ca2+ and the interactions between toxic Cd2+ and DREAM and other neuronal calcium sensors provide novel insight into the molecular mechanism of Cd2+ neurotoxicity.

Global Gene Knockout of Kcnip3 Enhances Pain Sensitivity and Exacerbates Negative Emotions in Rats.

The Ca2+-binding protein Kv channel interacting protein 3 (KChIP3) or downstream regulatory element antagonist modulator (DREAM), a member of the neuronal calcium sensor (NCS) family, shows remarkable multifunctional properties. It acts as a transcriptional repressor in the nucleus and a modulator of ion channels or receptors, such as Kv4, NMDA receptors and TRPV1 channels on the cytomembrane. Previous studies of Kcnip3-/- mice have indicated that KChIP3 facilitates pain hypersensitivity by repressing Pdyn expression in the spinal cord. Conversely, studies from transgenic daDREAM (dominant active DREAM) mice indicated that KChIP3 contributes to analgesia by repressing Bdnf expression and attenuating the development of central sensitization. To further determine the role of KChIP3 in pain transmission and its possible involvement in emotional processing, we assessed the pain sensitivity and negative emotional behaviors of Kcnip3-/- rats. The knockout rats showed higher pain sensitivity compared to the wild-type rats both in the acute nociceptive pain model and in the late phase (i.e., 2, 4 and 6 days post complete Freund’s adjuvant injection) of the chronic inflammatory pain model. Importantly, Kcnip3-/- rats displayed stronger aversion to the pain-associated compartment, higher anxiety level and aggravated depression-like behavior. Furthermore, RNA-Seq transcriptional profiling of the forebrain cortex were compared between wild-type and Kcnip3-/- rats. Among the 68 upregulated genes, 19 genes (including Nr4a2, Ret, Cplx3, Rgs9, and Itgad) are associated with neural development or synaptic transmission, particularly dopamine neurotransmission. Among the 79 downregulated genes, 16 genes (including Col3a1, Itm2a, Pcdhb3, Pcdhb22, Pcdhb20, Ddc, and Sncaip) are associated with neural development or dopaminergic transmission. Transcriptional upregulation of Nr4a2, Ret, Cplx3 and Rgs9, and downregulation of Col3a1, Itm2a, Pcdhb3 and Ddc, were validated by qPCR analysis. In summary, our studies showed that Kcnip3-/- rats displayed higher pain sensitivity and stronger negative emotions, suggesting an involvement of KChIP3 in negative emotions and possible role in central nociceptive processing.

Photoreceptor calcium sensor proteins in detergent-resistant membrane rafts are regulated via binding to caveolin-1

Rod cell membranes contain cholesterol-rich detergent-resistant membrane (DRM) rafts, which accumulate visual cascade proteins as well as proteins involved in regulation of phototransduction such as rhodopsin kinase and guanylate cyclases. Caveolin-1 is the major integral component of DRMs, possessing scaffolding and regulatory activities towards various signaling proteins. In this study, photoreceptor Ca2+-binding proteins recoverin, NCS1, GCAP1, and GCAP2, belonging to neuronal calcium sensor (NCS) family, were recognized as novel caveolin-1 interacting partners. All four NCS proteins co-fractionate with caveolin-1 in DRMs, isolated from illuminated bovine rod outer segments. According to pull-down assay, surface plasmon resonance spectroscopy and isothermal titration calorimetry data, they are capable of high-affinity binding to either N-terminal fragment of caveolin-1 (1–101), or its short scaffolding domain (81–101) via a novel structural site. In recoverin this site is localized in C-terminal domain in proximity to the third EF-hand motif and composed of aromatic amino acids conserved among NCS proteins. Remarkably, the binding of NCS proteins to caveolin-1 occurs only in the absence of calcium, which is in agreement with higher accessibility of the caveolin-1 binding site in their Ca2+-free forms. Consistently, the presence of caveolin-1 produces no effect on regulatory activity of Ca2+-saturated recoverin or NCS1 towards rhodopsin kinase, but upregulates GCAP2, which potentiates guanylate cyclase activity being in Ca2+-free conformation. In addition, the interaction with caveolin-1 decreases cooperativity and augments affinity of Ca2 + binding to recoverin apparently by facilitating exposure of its myristoyl group. We suggest that at low calcium NCS proteins are compartmentalized in photoreceptor rafts via binding to caveolin-1, which may enhance their activity or ensure their faster responses on Ca2+-signals thereby maintaining efficient phototransduction recovery and light adaptation.

Inhibition of DREAM-ATF6 interaction delays onset of cognition deficit in a mouse model of Huntington\u2019s disease

The transcriptional repressor DREAM (downstream regulatory element antagonist modulator) is a multifunctional neuronal calcium sensor (NCS) that controls Ca2+ and protein homeostasis through gene regulation and protein-protein interactions. Downregulation of DREAM is part of an endogenous neuroprotective mechanism that improves ATF6 (activating transcription factor 6) processing, neuronal survival in the striatum, and motor coordination in R6/2 mice, a model of Huntington’s disease (HD). Whether modulation of DREAM activity can also ameliorate cognition deficits in HD mice has not been studied. Moreover, it is not known whether DREAM downregulation in HD is unique, or also occurs for other NCS family members. Using the novel object recognition test, we show that chronic administration of the DREAM-binding molecule repaglinide, or induced DREAM haplodeficiency delays onset of cognitive impairment in R6/1 mice, another HD model. The mechanism involves a notable rise in the levels of transcriptionally active ATF6 protein in the hippocampus after repaglinide administration. In addition, we show that reduction in DREAM protein in the hippocampus of HD patients was not accompanied by downregulation of other NCS family members. Our results indicate that DREAM inhibition markedly improves ATF6 processing in the hippocampus and that it might contribute to a delay in memory decline in HD mice. The mechanism of neuroprotection through DREAM silencing in HD does not apply to other NCS family members.

Interactions of Neuronal Calcium Sensor Dream with Zinc

Maria J. Santiago Estevez and Jaroslava Miksovska Department of Chemistry and Biochemistry, Florida International University Neuronal calcium sensors regulate several physiological processes in the brain and are linked to numerous pathological conditions such as autism, Parkinson and Alzheimer disease. Downstream regulatory element antagonist modulator (DREAM) is among the neuronal calcium sensor family, it is an EF-hand protein highly expressed in the central nervous system in various areas such as the hippocampus and the neural cortex. It is responsible for regulating the kinetics of potassium channels, gene expression, calcium homeostasis and enzymatic activity of presenilin. The characterization of the metal-binding properties of DREAM and how it affects DREAM structure and DREAM interactions with effector proteins is fundamental to understand its biological function. Essential metals like Mg2+, Zn2+ and Ca2+ play extremely important roles in biological processes through direct interactions with proteins. DREAM carries out two Ca2+ binding EF hands and one Mg2+ binding EF hand, however, DREAM binding to other biologically significant metals is not very well known. Interactions of DREAM with Zn2+ have been monitored by using intrinsic and extrinsic fluorescent probes. Data shows that Zn2+ associates to DREAM with Kd ∼ 200 μM. Zn2+ and it does not compete for the same binding site as Ca2+ as the changes in the protein tertiary structure are distinct from those observed upon Ca2+association. Considering increased concentration of Zn2+ in neuronal tissue (150 - 200 μM), these results point towards the potential role of Zn2+ in modulating DREAM interactions with other intracellular proteins.

KChIP3 N-Terminal 31-50 Fragment Mediates Its Association with TRPV1 and Alleviates Inflammatory Hyperalgesia in Rats.

Potassium voltage-gated channel interacting protein 3 (KChIP3), also termed downstream regulatory element antagonist modulator (DREAM) and calsenilin, is a multifunctional protein belonging to the neuronal calcium sensor (NCS) family. Recent studies revealed the expression of KChIP3 in dorsal root ganglion (DRG) neurons, suggesting the potential role of KChIP3 in peripheral sensory processing. Herein, we show that KChIP3 colocalizes with transient receptor potential ion channel V1 (TRPV1), a critical molecule involved in peripheral sensitization during inflammatory pain. Furthermore, the N-terminal 31-50 fragment of KChIP3 is capable of binding both the intracellular N and C termini of TRPV1, which substantially decreases the surface localization of TRPV1 and the subsequent Ca2+ influx through the channel. Importantly, intrathecal administration of the transmembrane peptide transactivator of transcription (TAT)-31-50 remarkably reduces Ca2+ influx via TRPV1 in DRG neurons and alleviates thermal hyperalgesia and gait alterations in a complete Freund's adjuvant-induced inflammatory pain model in male rats. Moreover, intraplantar injection of TAT-31-50 attenuated the capsaicin-evoked spontaneous pain behavior and thermal hyperalgesia, which further strengthened the regulatory role of TAT-31-50 on TRPV1 channel. In addition, TAT-31-50 could also alleviate inflammatory thermal hyperalgesia in kcnip3-/- rats generated in our study, suggesting that the analgesic effect mediated by TAT-31-50 is independent of endogenous KChIP3. Our study reveals a novel peripheral mechanism for the analgesic function of KChIP3 and provides a potential analgesic agent, TAT-31-50, for the treatment of inflammatory pain.SIGNIFICANCE STATEMENT Inflammatory pain arising from inflamed or injured tissues significantly compromises the quality of life in patients. This study aims to elucidate the role of peripheral potassium channel interacting protein 3 (KChIP3) in inflammatory pain. Direct interaction of the KChIP3 N-terminal 31-50 fragment with transient receptor potential ion channel V1 (TRPV1) was demonstrated. The KChIP3-TRPV1 interaction reduces the surface localization of TRPV1 and thus alleviates heat hyperalgesia and gait alterations induced by peripheral inflammation. Furthermore, the transmembrane transactivator of transcription (TAT)-31-50 peptide showed analgesic effects on inflammatory hyperalgesia independently of endogenous KChIP3. This work reveals a novel mechanism of peripheral KChIP3 in inflammatory hyperalgesia that is distinct from its classical role as a transcriptional repressor in pain modulation.

Identification of critical amino acid residues and functional conservation of the Neurospora crassa and Rattus norvegicus orthologues of neuronal calcium sensor-1.

Neuronal calcium sensor-1 (NCS-1) is a member of neuronal calcium sensor family of proteins consisting of an amino terminal myristoylation domain and four conserved calcium (Ca2+) binding EF-hand domains. We performed site-directed mutational analysis of three key amino acid residues that are glycine in the conserved site for the N-terminal myristoylation, a conserved glutamic acid residue responsible for Ca2+ binding in the third EF-hand (EF3), and an unusual non-conserved amino acid arginine at position 175 in the Neurospora crassa NCS-1. The N. crassa strains possessing the ncs-1 mutant allele of these three amino acid residues showed impairment in functions ranging from growth, Ca2+ stress tolerance, and ultraviolet survival. In addition, heterologous expression of the NCS-1 from Rattus norvegicus in N. crassa confirmed its interspecies functional conservation. Moreover, functions of glutamic acid at position 120, the first Ca2+ binding residue among all the EF-hands of the R. norvegicus NCS-1 was found conserved. Thus, we identified three critical amino acid residues of N. crassa NCS-1, and demonstrated its functional conservation across species using the orthologue from R. norvegicus.

Proteome-wide Identification of Novel Ceramide-binding Proteins by Yeast Surface cDNA Display and Deep Sequencing

Although the bioactive sphingolipid ceramide is an important cell signaling molecule, relatively few direct ceramide-interacting proteins are known. We used an approach combining yeast surface cDNA display and deep sequencing technology to identify novel proteins binding directly to ceramide. We identified 234 candidate ceramide-binding protein fragments and validated binding for 20. Most (17) bound selectively to ceramide, although a few (3) bound to other lipids as well. Several novel ceramide-binding domains were discovered, including the EF-hand calcium-binding motif, the heat shock chaperonin-binding motif STI1, the SCP2 sterol-binding domain, and the tetratricopeptide repeat region motif. Interestingly, four of the verified ceramide-binding proteins (HPCA, HPCAL1, NCS1, and VSNL1) and an additional three candidate ceramide-binding proteins (NCALD, HPCAL4, and KCNIP3) belong to the neuronal calcium sensor family of EF hand-containing proteins. We used mutagenesis to map the ceramide-binding site in HPCA and to create a mutant HPCA that does not bind to ceramide. We demonstrated selective binding to ceramide by mammalian cell-produced wild type but not mutant HPCA. Intriguingly, we also identified a fragment from prostaglandin D2synthase that binds preferentially to ceramide 1-phosphate. The wide variety of proteins and domains capable of binding to ceramide suggests that many of the signaling functions of ceramide may be regulated by direct binding to these proteins. Based on the deep sequencing data, we estimate that our yeast surface cDNA display library covers ∼60% of the human proteome and our selection/deep sequencing protocol can identify target-interacting protein fragments that are present at extremely low frequency in the starting library. Thus, the yeast surface cDNA display/deep sequencing approach is a rapid, comprehensive, and flexible method for the analysis of protein-ligand interactions, particularly for the study of non-protein ligands.

Electrophoretic mobility shift in native gels indicates calcium-dependent structural changes of neuronal calcium sensor proteins

In proteins of the neuronal calcium sensor (NCS) family, changes in structure as well as function are brought about by the binding of calcium. In this article, we demonstrate that these structural changes, solely due to calcium binding, can be assessed through electrophoresis in native gels. The results demonstrate that the NCS proteins undergo ligand-dependent conformational changes that are detectable in native gels as a gradual decrease in mobility with increasing calcium but not other tested divalent cations such as magnesium, strontium, and barium. Surprisingly, such a gradual change over the entire tested range is exhibited only by the NCS proteins but not by other tested calcium-binding proteins such as calmodulin and S100B, indicating that the change in mobility may be linked to a unique NCS family feature—the calcium–myristoyl switch. Even within the NCS family, the changes in mobility are characteristic of the protein, indicating that the technique is sensitive to the individual features of the protein. Thus, electrophoretic mobility on native gels provides a simple and elegant method to investigate calcium (small ligand)-induced structural changes at least in the superfamily of NCS proteins.

Neuronal Calcium Sensor-1 Binds the D2 Dopamine Receptor and G-protein-coupled Receptor Kinase 1 (GRK1) Peptides Using Different Modes of Interactions

Neuronal calcium sensor-1 (NCS-1) is the primordial member of the neuronal calcium sensor family of EF-hand Ca(2+)-binding proteins. It interacts with both the G-protein-coupled receptor (GPCR) dopamine D2 receptor (D2R), regulating its internalization and surface expression, and the cognate kinases GRK1 and GRK2. Determination of the crystal structures of Ca(2+)/NCS-1 alone and in complex with peptides derived from D2R and GRK1 reveals that the differential recognition is facilitated by the conformational flexibility of the C-lobe-binding site. We find that two copies of the D2R peptide bind within the hydrophobic crevice on Ca(2+)/NCS-1, but only one copy of the GRK1 peptide binds. The different binding modes are made possible by the C-lobe-binding site of NCS-1, which adopts alternative conformations in each complex. C-terminal residues Ser-178-Val-190 act in concert with the flexible EF3/EF4 loop region to effectively form different peptide-binding sites. In the Ca(2+)/NCS-1·D2R peptide complex, the C-terminal region adopts a 310 helix-turn-310 helix, whereas in the GRK1 peptide complex it forms an α-helix. Removal of Ser-178-Val-190 generated a C-terminal truncation mutant that formed a dimer, indicating that the NCS-1 C-terminal region prevents NCS-1 oligomerization. We propose that the flexible nature of the C-terminal region is essential to allow it to modulate its protein-binding sites and adapt its conformation to accommodate both ligands. This appears to be driven by the variability of the conformation of the C-lobe-binding site, which has ramifications for the target specificity and diversity of NCS-1.

Ca2+ and Mg2+ modulate conformational dynamics and stability of downstream regulatory element antagonist modulator

Downstream Regulatory Element Antagonist Modulator (DREAM) belongs to the family of neuronal calcium sensors (NCS) that transduce the intracellular changes in Ca(2+) concentration into a variety of responses including gene expression, regulation of Kv channel activity, and calcium homeostasis. Despite the significant sequence and structural similarities with other NCS members, DREAM shows several features unique among NCS such as formation of a tetramer in the apo-state, and interactions with various intracellular biomacromolecules including DNA, presenilin, Kv channels, and calmodulin. Here we use spectroscopic techniques in combination with molecular dynamics simulation to study conformational changes induced by Ca(2+) /Mg(2+) association to DREAM. Our data indicate a minor impact of Ca(2+) association on the overall structure of the N- and C-terminal domains, although Ca(2+) binding decreases the conformational heterogeneity as evident from the decrease in the fluorescence lifetime distribution in the Ca(2+) bound forms of the protein. Time-resolved fluorescence data indicate that Ca(2+) binding triggers a conformational transition that is characterized by more efficient quenching of Trp residue. The unfolding of DREAM occurs through an partially unfolded intermediate that is stabilized by Ca(2+) association to EF-hand 3 and EF-hand 4. The native state is stabilized with respect to the partially unfolded state only in the presence of both Ca(2+) and Mg(2+) suggesting that, under physiological conditions, Ca(2+) free DREAM exhibits a high conformational flexibility that may facilitate its physiological functions.

The N-Terminal Extension of KChIP3 is Responsible for KChIP3-Calmodulin Complex Formation

Potassium channel interacting proteins (KChIPs), belong to the family of neuronal calcium sensors that are expressed in brain, lung and heart tissue. KChIPs bind to Kv4 channels and regulate channel trafficking, membrane association, and current kinetics. Among them, KChIP-3, also known as Downstream Regulatory Element Antagonistic Modulator (DREAM) and calsenilin, interacts with other intracellular partners (presenilin, calmodulin, and DNA) and was implied in Alzheimer's disease and pain sensing, although a molecular mechanism of KChIP-3 interactions with distinct intracellular partners remains unknown. The objective of this study is to provide a molecular insight into the mechanism of KChIP-3 interactions with calmodulin and determine the role of the N-terminus of KChIP-3 in the formation of calmodulin:KChIP-3 complex. Full length KChIP-3 (residue 1-256) and ΔN KChIP-3 (residue 65-256) were over-expressed in E. coli and purified according to an established protocol. In addition, a peptide that corresponds to residues 29-44 in KChIP-3 N-terminus was synthesized. The equilibrium dissociation constants and rotational correlation times for calmodulin: KChIP-3 complexes were determined using fluorescence anisotropy. Molecular dynamic simulations were implemented to provide an insight into the potential molecular structure of the calmodulin:KChIP-3 protein complex. Calmodulin interaction with KChIP-3 shows a Kd=3.3 µM whereas the peptide analogous to KChIP-3(29-44) binds with Kd=150 nM, deletion of 64 residues from the KChIP-3 N-terminus abolishes the complex formation. The interactions between KChIP-3 and calmodulin are regulated by the presence of Ca2+. A rotational correlation time of 35ns was determined for the KChIP-3:calmodulin complex, in agreement with a heterodimer of ellipsoidal shape. These results show that interactions between calmodulin and KChIP-3 are controlled by the intracellular calcium concentration and that the N-terminal extension in KChIP-3 provides a binding interface for calmodulin.

NCS-1 deficiency causes anxiety and depressive-like behavior with impaired non-aversive memory in mice

Sensing and regulating intracellular levels of calcium are essential for proper cellular function. In neurons, calcium sensing plays important roles in neuronal plasticity, neurotransmitter release, long-term synapse modification and ion channel activity. Neuronal calcium sensor-1 (NCS-1) is a member of the highly conserved neuronal calcium sensor family. Although NCS-1 has been associated with psychiatric conditions including autism, bipolar disorder and schizophrenia, it is unclear which role NCS-1 plays in behavior. To understand the involvement of NCS-1 in psychiatric conditions, we provided a comprehensive behavioral characterization of NCS-1 knockout (KO) mice. These mice grow and develop normally without apparent abnormalities in comparison to wild type littermates. However, open field showed that NCS-1 deficiency impairs novelty-induced exploratory activity in both KO and heterozygote (HT) mice. Moreover, NCS-1-deficiency also resulted in anxiety- and depressive-like behaviors as demonstrated by elevated plus maze, large open field, forced swim and tail suspension tasks. Furthermore, based on spontaneous object recognition test, non-aversive long-term memory was impaired in NCS-1 KO mice. In contrast, neither social behavior nor a kind of aversive memory was affected under NCS-1 deficiency. These data implicate NCS-1 in exploratory activity, memory and mood-related behaviors, suggesting that NCS-1 gene ablation may result in phenotypic abnormalities associated with neuropsychiatric disorders.

The Thermal Stability of Recoverin Depends on Calcium Binding and Its Myristoyl Moiety As Revealed by Infrared Spectroscopy

To evaluate the structural stability of recoverin, a member of the neuronal calcium sensor family, the effect of temperature, myristoylation, and calcium:protein molar ratio on its secondary structure has been studied by transmission infrared spectroscopy. On the basis of the data, the protein predominantly adopts α-helical structures (∼50-55%) with turns, unordered structures, and β-sheets at 25 °C. The data show no significant impact of the presence of calcium and myristoylation on secondary structure. It is found that, in the absence of calcium, recoverin denatures and self-aggregates while being heated, with the formation of intermolecular antiparallel β-sheets. The nonmyristoylated protein (Rec-nMyr) exhibits a lower temperature threshold of aggregation and a higher intermolecular β-sheet content at 65 °C than the myristoylated protein (Rec-Myr). The former thus appears to be less thermally stable than the latter. In the presence of excess calcium ions (calcium:protein ratio of 10), the protein is thermally stable up to 65 °C with no significant conformational change, the presence of the myristoyl chain having no effect on the thermal stability of recoverin under these conditions. A decrease in the thermal stability of recoverin is observed as the calcium:protein molar ratio decreases, with Rec-nMyr being less stable than Rec-Myr. The data overall suggest that a minimal number of coordinated calcium ions is necessary to fully stabilize the structure of recoverin and that, when bound to the membrane, i.e., when the myristoyl chain protrudes from the interior pocket, recoverin should be more stable than in a Ca-free solution, i.e., when the myristoyl chain is sequestered in the interior.

Identification of key structural elements for neuronal calcium sensor-1 function in the regulation of the temperature-dependency of locomotion in C. elegans

BackgroundIntracellular Ca2+ regulates many aspects of neuronal function through Ca2+ binding to EF hand-containing Ca2+ sensors that in turn bind target proteins to regulate their function. Amongst the sensors are the neuronal calcium sensor (NCS) family of proteins that are involved in multiple neuronal signalling pathways. Each NCS protein has specific and overlapping targets and physiological functions and specificity is likely to be determined by structural features within the proteins. Common to the NCS proteins is the exposure of a hydrophobic groove, allowing target binding in the Ca2+-loaded form. Structural analysis of NCS protein complexes with target peptides has indicated common and distinct aspects of target protein interaction. Two key differences between NCS proteins are the size of the hydrophobic groove that is exposed for interaction and the role of their non-conserved C-terminal tails.ResultsWe characterised the role of NCS-1 in a temperature-dependent locomotion assay in C. elegans and identified a distinct phenotype in the ncs-1 null in which the worms do not show reduced locomotion at actually elevated temperature. Using rescue of this phenotype we showed that NCS-1 functions in AIY neurons. Structure/function analysis introducing single or double mutations within the hydrophobic groove based on information from characterised target complexes established that both N- and C-terminal pockets of the groove are functionally important and that deletion of the C-terminal tail of NCS-1 did not impair its ability to rescue.ConclusionsThe current work has allowed physiological assessment of suggestions from structural studies on the key structural features that underlie the interaction of NCS-1 with its target proteins. The results are consistent with the notion that full length of the hydrophobic groove is required for the regulatory interactions underlying NCS-1 function whereas the C-terminal tail of NCS-1 is not essential. This has allowed discrimination between two potential modes of interaction of NCS-1 with its targets.

Spectroscopic Study Ca2+ Induced Changes in the Structure, Dynamics and Stability of Dream Protein and its Mechanism of DNA Interaction

Downstream Regulatory Element Antagonist Modulator (DREAM)/Calsenilin/KchIP3 is a multifunctional calcium binding protein that belongs to the EF-hand branch of Neuronal Calcium Sensor family. DREAM associates to Downstream Regulatory Element (DRE) of prodynorphin and c-fos genes and blocks their transcription in a calcium-regulated manner. Other molecular functions of DREAM involve proteolytic processing of presenilins, modulation of A-type current of potassium channels, and regulation of neuronal apoptosis. Previously, we have studied Mg2+ and Ca2+ induced changes in structure and dynamics of DREAM and its C-terminal domain. Recently, we have investigated the contribution of individual EF hands (EF-2, EF-3, and EF-4) to Ca2+ triggered conformational transition in DREAM by characterizing fluorescence properties of D150N, E186Q, and E234Q mutants. The tryptophan 169 emission and lifetime properties are strongly influenced by Ca2+ association to EF-3 whereas the ligand association to EF-2 and/or EF-4 has a minor impact on Trp fluorescence suggesting that Ca2+ association to EF-3 is crucial to induced structural changes within the hydrophobic pocket between EF-2 and EF-3. In addition, association of 25-mer oligonucleotide of prodynorphin gene to DREAM was characterized using ITC. DNA association to DREAM is temperature dependent. ApoDREAM strongly binds to DynDRE at 35oC (Kd1 =206 nM, Kd2 = 24 µM) whereas weaker interactions were observed at at 25oC). Very weak binding with Kd = 91 µM and Kd = 200 µM was observed for DREAM-DynDRE association in the presence of Mg2+ and Ca2+, respectively. These results support the mechanism that ApoDREAM strongly binds to DynDRE to block prodynorphin gene transcription and the DREAM-DynDRE complex reversibly dissociates upon Ca2+ binding.

The Neuronal Calcium Sensor Protein Acrocalcin: A Potential Target of Calmodulin Regulation during Development in the Coral Acropora millepora

To understand the calcium-mediated signalling pathways underlying settlement and metamorphosis in the Scleractinian coral Acropora millepora, a predicted protein set derived from larval cDNAs was scanned for the presence of EF-hand domains (Pfam Id: PF00036). This approach led to the identification of a canonical calmodulin (AmCaM) protein and an uncharacterised member of the Neuronal Calcium Sensor (NCS) family of proteins known here as Acrocalcin (AmAC). While AmCaM transcripts were present throughout development, AmAC transcripts were not detected prior to gastrulation, after which relatively constant mRNA levels were detected until metamorphosis and settlement. The AmAC protein contains an internal CaM-binding site and was shown to interact in vitro with AmCaM. These results are consistent with the idea that AmAC is a target of AmCaM in vivo, suggesting that this interaction may regulate calcium-dependent processes during the development of Acropora millepora.

The Potassium Channel Interacting Protein 3 (DREAM/KChIP3) Heterodimerizes with and Regulates Calmodulin Function

Downstream regulatory element antagonistic modulator (DREAM/KChIP3), a neuronal EF-hand protein, modulates pain, potassium channel activity, and binds presenilin 1. Using affinity capture of neuronal proteins by immobilized DREAM/KChIP3 in the presence and absence of calcium (Ca(2+)) followed by mass spectroscopic identification of interacting proteins, we demonstrate that in the presence of Ca(2+), DREAM/KChIP3 interacts with the EF-hand protein, calmodulin (CaM). The interaction of DREAM/KChIP3 with CaM does not occur in the absence of Ca(2+). In the absence of Ca(2+), DREAM/KChIP3 binds the EF-hand protein, calcineurin subunit-B. Ca(2+)-bound DREAM/KChIP3 binds CaM with a dissociation constant of ∼3 μM as assessed by changes in DREAM/KChIP3 intrinsic protein fluorescence in the presence of CaM. Two-dimensional (1)H,(15)N heteronuclear single quantum coherence spectra reveal changes in chemical shifts and line broadening upon the addition of CaM to (15)N DREAM/KChIP3. The amino-terminal portion of DREAM/KChIP3 is required for its binding to CaM because a construct of DREAM/KChIP3 lacking the first 94 amino-terminal residues fails to bind CaM as assessed by fluorescence spectroscopy. The addition of Ca(2+)-bound DREAM/KChIP3 increases the activation of calcineurin (CN) by calcium CaM. A DREAM/KChIP3 mutant incapable of binding Ca(2+) also stimulates calmodulin-dependent CN activity. The shortened form of DREAM/KChIP3 lacking the NH(2)-terminal amino acids fails to activate CN in the presence of calcium CaM. Our data demonstrate the interaction of DREAM/KChIP3 with the important EF-hand protein, CaM, and show that the interaction alters CN activity.