A T-type channel-calmodulin complex triggers ?CaMKII activation.
Ontology highlight
ABSTRACT:
SUBMITTER: Asmara H
PROVIDER: S-EPMC5553682 | biostudies-literature | 2017 Aug
REPOSITORIES: biostudies-literature
Publications
A T-type channel-calmodulin complex triggers αCaMKII activation.
Asmara Hadhimulya H Micu Ileana I Rizwan Arsalan P AP Sahu Giriraj G Simms Brett A BA Zhang Fang-Xiong FX Engbers Jordan D T JDT Stys Peter K PK Zamponi Gerald W GW Turner Ray W RW
Molecular brain 20170811 1
Calmodulin (CaM) is an important signaling molecule that regulates a vast array of cellular functions by activating second messengers involved in cell function and plasticity. Low voltage-activated calcium channels of the Cav3 family have the important role of mediating low threshold calcium influx, but were not believed to interact with CaM. We find a constitutive association between CaM and the Cav3.1 channel at rest that is lost through an activity-dependent and Cav3.1 calcium-dependent CaM d ...[more]
Similar Datasets
Project description:Small-conductance Ca2+-activated K+ (SK) channels mediate neuron excitability and are associated with synaptic transmission and plasticity. They also regulate immune responses and the size of blood cells. Activation of SK channels requires calmodulin (CaM), but how CaM binds and opens SK channels has been unclear. Here we report cryo-electron microscopy (cryo-EM) structures of a human SK4-CaM channel complex in closed and activated states at 3.4- and 3.5-angstrom resolution, respectively. Four CaM molecules bind to one channel tetramer. Each lobe of CaM serves a distinct function: The C-lobe binds to the channel constitutively, whereas the N-lobe interacts with the S4-S5 linker in a Ca2+-dependent manner. The S4-S5 linker, which contains two distinct helices, undergoes conformational changes upon CaM binding to open the channel pore. These structures reveal the gating mechanism of SK channels and provide a basis for understanding SK channel pharmacology.
| S-EPMC6241251 | biostudies-literature
Project description:L-type voltage-gated Ca2+ channels (CaV1.2 and CaV1.3, called CaV) interact with the Ca2+ sensor proteins, calmodulin (CaM) and Ca2+ binding Protein 1 (CaBP1), that oppositely control Ca2+-dependent channel activity. CaM and CaBP1 can each bind to the IQ-motif within the C-terminal cytosolic domain of CaV, which promotes increased channel open probability under basal conditions. At elevated cytosolic Ca2+ levels (caused by CaV channel opening), Ca2+-bound CaM binding to CaV is essential for promoting rapid Ca2+-dependent channel inactivation (CDI). By contrast, CaV binding to CaBP1 prevents CDI and promotes Ca2+-induced channel opening (called CDF). In this review, I provide an overview of the known structures of CaM and CaBP1 and their structural interactions with the IQ-motif to help understand how CaM promotes CDI, whereas CaBP1 prevents CDI and instead promotes CDF. Previous electrophysiology studies suggest that Ca2+-free forms of CaM and CaBP1 may pre-associate with CaV under basal conditions. However, previous Ca2+ binding data suggest that CaM and CaBP1 are both calculated to bind to Ca2+ with an apparent dissociation constant of ~100 nM when CaM or CaBP1 is bound to the IQ-motif. Since the neuronal basal cytosolic Ca2+ concentration is ~100 nM, nearly half of the neuronal CaV channels are suggested to be bound to Ca2+-bound forms of either CaM or CaBP1 under basal conditions. The pre-association of CaV with calcified forms of CaM or CaBP1 are predicted here to have functional implications. The Ca2+-bound form of CaBP1 is proposed to bind to CaV under basal conditions to block CaV binding to CaM, which could explain how CaBP1 might prevent CDI.
| S-EPMC8699282 | biostudies-literature
Project description:All subtypes of KCNQ channel subunits (KCNQ1-5) require calmodulin as a co-factor for functional channels. It has been demonstrated that calmodulin plays a critical role in KCNQ channel trafficking as well as calcium-mediated current modulation. However, how calcium-bound calmodulin suppresses the M-current is not well understood. In this study, we investigated the molecular mechanism of KCNQ2 current suppression mediated by calcium-bound calmodulin. We show that calcium induced slow calmodulin dissociation from the KCNQ2 channel subunit. In contrast, in homomeric KCNQ3 channels, calcium facilitated calmodulin binding. We demonstrate that this difference in calmodulin binding was due to the unique cysteine residue in the KCNQ2 subunit at aa 527 in Helix B, which corresponds to an arginine residue in other KCNQ subunits including KCNQ3. In addition, a KCNQ2 channel associated protein AKAP79/150 (79 for human, 150 for rodent orthologs) also preferentially bound calcium-bound calmodulin. Therefore, the KCNQ2 channel complex was able to retain calcium-bound calmodulin either through the AKPA79/150 or KCNQ3 subunit. Functionally, increasing intracellular calcium by ionomycin suppressed currents generated by KCNQ2, KCNQ2(C527R) or heteromeric KCNQ2/KCNQ3 channels to an equivalent extent. This suggests that a change in the binding configuration, rather than dissociation of calmodulin, is responsible for KCNQ current suppression. Furthermore, we demonstrate that KCNQ current suppression was accompanied by reduced KCNQ affinity toward phosphatidylinositol 4,5-bisphosphate (PIP2) when assessed by a voltage-sensitive phosphatase, Ci-VSP. These results suggest that a rise in intracellular calcium induces a change in the configuration of CaM-KCNQ binding, which leads to the reduction of KCNQ affinity for PIP2 and subsequent current suppression.
| S-EPMC3857245 | biostudies-literature
Project description:The Ca(2+)-activated Cl channel anoctamin-1 (Ano1; Tmem16A) plays a variety of physiological roles, including epithelial fluid secretion. Ano1 is activated by increases in intracellular Ca(2+), but there is uncertainty whether Ca(2+) binds directly to Ano1 or whether phosphorylation or additional Ca(2+)-binding subunits like calmodulin (CaM) are required. Here we show that CaM is not necessary for activation of Ano1 by Ca(2+) for the following reasons. (a) Exogenous CaM has no effect on Ano1 currents in inside-out excised patches. (b) Overexpression of Ca(2+)-insensitive mutants of CaM have no effect on Ano1 currents, whereas they eliminate the current mediated by the small-conductance Ca(2+)-activated K(+) (SK2) channel. (c) Ano1 does not coimmunoprecipitate with CaM, whereas SK2 does. Furthermore, Ano1 binds very weakly to CaM in pull-down assays. (d) Ano1 is activated in excised patches by low concentrations of Ba(2+), which does not activate CaM. In addition, we conclude that reversible phosphorylation/dephosphorylation is not required for current activation by Ca(2+) because the current can be repeatedly activated in excised patches in the absence of ATP or other high-energy compounds. Although Ano1 is blocked by the CaM inhibitor trifluoperazine (TFP), we propose that TFP inhibits the channel in a CaM-independent manner because TFP does not inhibit Ano1 when applied to the cytoplasmic side of excised patches. These experiments lead us to conclude that CaM is not required for activation of Ano1 by Ca(2+). Although CaM is not required for channel opening by Ca(2+), work of other investigators suggests that CaM may have effects in modulating the biophysical properties of the channel.
| S-EPMC4001774 | biostudies-literature
Project description:Calmodulin (CaM) in complex with Ca(2+) channels constitutes a prototype for Ca(2+) sensors that are intimately colocalized with Ca(2+) sources. The C-lobe of CaM senses local, large Ca(2+) oscillations due to Ca(2+) influx from the host channel, and the N-lobe senses global, albeit diminutive Ca(2+) changes arising from distant sources. Though biologically essential, the mechanism underlying global Ca(2+) sensing has remained unknown. Here, we advance a theory of how global selectivity arises, and we experimentally validate this proposal with methodologies enabling millisecond control of Ca(2+) oscillations seen by the CaM/channel complex. We find that global selectivity arises from rapid Ca(2+) release from CaM combined with greater affinity of the channel for Ca(2+)-free versus Ca(2+)-bound CaM. The emergence of complex decoding properties from the juxtaposition of common elements, and the techniques developed herein, promise generalization to numerous molecules residing near Ca(2+) sources.
| S-EPMC4262405 | biostudies-literature
Project description:Kv7.4 (KCNQ4) voltage-gated potassium channels control excitability in the inner ear and the central auditory pathway. Mutations in Kv7.4 channels result in inherited progressive deafness in humans. Calmodulin (CaM) is crucial for regulating Kv7 channels, but how CaM affects Kv7 activity has remained unclear. Here, based on electrophysiological recordings, we report that the third EF hand (EF3) of CaM controls the calcium-dependent regulation of Kv7.4 activation and that the S2-S3 loop of Kv7.4 is essential for the regulation mediated by CaM. Overexpression of the mutant CaM1234, which loses the calcium binding ability of all four EF hands, facilitates Kv7.4 activation by accelerating activation kinetics and shifting the voltage dependence of activation leftwards. The single mutant CaM3, which loses the calcium binding ability of the EF3, phenocopies facilitating effects of CaM1234 on Kv7.4 activation. Kv7.4 channels co-expressed with wild-type (WT) CaM show inhibited activation when intracellular calcium levels increase, while Kv7.4 channels co-expressed with CaM1234 or CaM3 are insensitive to calcium. Mutations C156A, C157A, C158V, R159, and R161A, which are located within the Kv7.4 S2-S3 loop, dramatically facilitate activation of Kv7.4 channels co-expressed with WT CaM but have no effect on activation of Kv7.4 channels co-expressed with CaM3, indicating that these five mutations decrease the inhibitory effect of Ca2+/CaM. The double mutation C156A/R159A decreases Ca2+/CaM binding and completely abolishes CaM-mediated calcium-dependent regulation of Kv7.4 activation. Taken together, our results provide mechanistic insights into CaM regulation of Kv7.4 activation and highlight the crucial role of the Kv7.4 S2-S3 loop in CaM regulation.
| S-EPMC7854705 | biostudies-literature
Project description:P-type (CaV2.1) Ca2+ channels are a central conduit of neuronal Ca2+ entry, so their Ca2+ feedback regulation promises widespread neurobiological impact. Heterologous expression of recombinant CaV2.1 channels demonstrates that the Ca2+ sensor calmodulin can trigger Ca2+-dependent facilitation (CDF) of channel opening. This facilitation occurs when local Ca2+ influx through individual channels selectively activates the C-terminal lobe of calmodulin. In neurons, however, such calmodulin-mediated processes have yet to be detected, and CDF of native P-type current has thus far appeared different, arguably triggered by other Ca2+ sensing molecules. Here, in cerebellar Purkinje somata abundant with prototypic P-type channels, we find that the C-terminal lobe of calmodulin does produce CDF, and such facilitation augments Ca2+ entry during stimulation by repetitive action-potential and complex-spike waveforms. Beyond recapitulating key features of recombinant channels, these neurons exhibit an additional modulatory dimension: developmental upregulation of CDF during postnatal week 2. This phenomenon reflects increasing somatic expression of CaV2.1 splice variants that manifest CDF and progressive dendritic targeting of variants lacking CDF. Calmodulin-triggered facilitation is thus fundamental to native CaV2.1 and rapidly enhanced during early development.
| S-EPMC6725527 | biostudies-literature
Project description:Increased "persistent" current, caused by delayed inactivation, through voltage-gated Na+ (NaV) channels leads to cardiac arrhythmias or epilepsy. The underlying molecular contributors to these inactivation defects are poorly understood. Here, we show that calmodulin (CaM) binding to multiple sites within NaV channel intracellular C-terminal domains (CTDs) limits persistent Na+ current and accelerates inactivation across the NaV family. Arrhythmia or epilepsy mutations located in NaV1.5 or NaV1.2 channel CTDs, respectively, reduce CaM binding either directly or by interfering with CTD-CTD interchannel interactions. Boosting the availability of CaM, thus shifting its binding equilibrium, restores wild-type (WT)-like inactivation in mutant NaV1.5 and NaV1.2 channels and likewise diminishes the comparatively large persistent Na+ current through WT NaV1.6, whose CTD displays relatively low CaM affinity. In cerebellar Purkinje neurons, in which NaV1.6 promotes a large physiological persistent Na+ current, increased CaM diminishes the persistent Na+ current, suggesting that the endogenous, comparatively weak affinity of NaV1.6 for apoCaM is important for physiological persistent current.
| S-EPMC5299624 | biostudies-literature
Project description:UnlabelledLong-term potentiation (LTP), a long-lasting enhancement in communication between neurons, is considered to be the major cellular mechanism underlying learning and memory. LTP triggers high-frequency calcium pulses that result in the activation of Calcium/Calmodulin (CaM)-dependent kinase II (CaMKII). CaMKII acts as a molecular switch because it remains active for a long time after the return to basal calcium levels, which is a unique property required for CaMKII function. Here we describe the crystal structure of the human CaMKIIdelta/Ca2+/CaM complex, structures of all four human CaMKII catalytic domains in their autoinhibited states, as well as structures of human CaMKII oligomerization domains in their tetradecameric and physiological dodecameric states. All four autoinhibited human CaMKIIs were monomeric in the determined crystal structures but associated weakly in solution. In the CaMKIIdelta/Ca2+/CaM complex, the inhibitory region adopted an extended conformation and interacted with an adjacent catalytic domain positioning T287 into the active site of the interacting protomer. Comparisons with autoinhibited CaMKII structures showed that binding of calmodulin leads to the rearrangement of residues in the active site to a conformation suitable for ATP binding and to the closure of the binding groove for the autoinhibitory helix by helix alphaD. The structural data, together with biophysical interaction studies, reveals the mechanism of CaMKII activation by calmodulin and explains many of the unique regulatory properties of these two essential signaling molecules.Enhanced versionThis article can also be viewed as an enhanced version in which the text of the article is integrated with interactive 3-D representations and animated transitions. Please note that a web plugin is required to access this enhanced functionality. Instructions for the installation and use of the Web plugin are available in Text S1.
| S-EPMC2910593 | biostudies-literature
Project description:IntroductionErectile dysfunction (ED) is frequently encountered in patients with arterial hypertension and there is a recent functional correlation between the expression of thermoreceptor channels TRPM8 (melastatin 8) and alterations in blood pressure in hypertension. The aim of this study was to investigate the function of cold-sensing TRPM8 channel in internal pudendal artery (IPA) in both normotensive and hypertensive rats.MethodsWe performed experiments integrating physiological, pharmacological, biochemical and cellular techniques.ResultsTRPM8 channels are expressed in the IPA and in vascular smooth muscle cells from IPA. In addition, TRPM8 activation, by both a cooling compound icilin (82.1 ± 3.0%, n = 6) and cold temperature [thermal stimulus, basal tone (25 °C, 41.2 ± 3.4%, n = 5) or pre-contracted tone induced by phenylephrine (25 °C, 87.0 ± 3.6%, n = 7)], induced relaxation in IPA. Furthermore, the results showed that the concentration-response curve to icilin was significantly shifted to the right in different conditions, such as: the absence of the vascular endothelium, in the presence of L-NAME (10-4 M), or indomethacin (10-5 M) or by a combination of charybdotoxin (10-7 M) and apamin (5 × 10-6 M), and Y27632 (10-6 M). Interestingly, icilin-induced vasodilation was significantly higher in IPA from spontaneously hypertensive (SHR, E10-4M = 75.3 ± 1.7%) compared to wistar rats (E10-4M = 56.4 ± 2.6%), despite no changes in the TRPM8 expression in IPA between the strains, suggesting that the sensitivity of TRPM8 channels is higher in SHR.ConclusionsThese data demonstrate for the first time, the expression and function of TRPM8 channels in the IPA involving, at least in part, endothelium-derived relaxing factors and ROCK inhibition. Overall, this channel could potentially be a new target for the treatment of hypertension associated-ED.
| S-EPMC6733625 | biostudies-literature