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Convulsant agents activate c-fos induction in both a calmodulin-dependent and calmodulin-independent manner.

Calcium acts as a second messenger and can enter neurons through several types of calcium channel. We sought to determine whether the calcium-dependent mechanisms inducing c-fos expression are identical following activation, by appropriate drugs, of L-type voltage-sensitive calcium channels or NMDA and non-NMDA receptors or following inhibition of the GABAergic system. We used primary cortical neurons and OF1 mice, and the levels of c-fos protein and c-fos mRNA were detected after treatment with the drugs by means of immunocytochemistry and in situ hybridization. The calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) abolished gamma-hexachlorocyclohexane-, Bay K 8644-, pentylenetetrazole-, and kainic acid-induced increases in c-fos expression in cultured neurons. Conversely, W-7 did not affect either NMDA- or picrotoxinin-mediated increases in c-fos expression. In mice, the pattern of protooncogene expression displayed some differences compared with cultured neurons, depending on the treatment. W-7 administered before gamma-hexachlorocyclohexane, Bay K 8644, or pentylenetetrazole blocked the expression of c-fos elicited by these compounds. However, W-7 was not able to abolish c-fos expression induced by picrotoxinin. In the animals treated with W-7 before kainic acid or NMDA administration, c-fos expression was inhibited in cerebral cortex, but it was still present in hippocampus. These results agree with the existence of diverse mechanisms transducing the calcium signals to the nucleus. Calmodulin may mediate neuronal responses depending on the route by which calcium enters the neuron, resulting in activation of different enzymes.

Animals↗

The calmodulin-binding domain from a plant kinesin functions as a modular domain in conferring Ca2+-calmodulin regulation to animal plus- and minus-end kinesins.

Plant kinesin-like calmodulin-binding protein (KCBP) is a novel member of the kinesin superfamily that interacts with calmodulin (CaM) via its CaM-binding domain (CBD). Activated CaM (Ca(2+)-CaM) has been shown to inhibit KCBP interaction with microtubules (MTs) thereby abolishing its motor- and MT-dependent ATPase activities. To test whether the fusion of CBD to non-CaM-binding kinesins confers Ca(2+)-CaM regulation, we fused the CBD of KCBP to the N or C terminus of a minus-end (non-claret disjunction) or C terminus of a plus-end (Drosophila kinesin) motor. Purified chimeric kinesins bound CaM in a Ca(2+)-dependent manner whereas non-claret disjunction, Drosophila kinesin, and KCBP that lack a CBD did not. As in the case of KCBP with CBD, the interaction of chimeric motors with MTs, as well as their MT-stimulated ATPase activity, was inhibited by Ca(2+)-CaM. The presence of a spacer between the motor and CBD did not alter Ca(2+)-CaM regulation. However, KCBP interaction with MTs and its MT-stimulated ATPase activity were not inhibited when the motor domain and CBD were added separately, suggesting that Ca(2+)-CaM regulation of CaM-binding motors occurs only when the CBD is attached to the motor domain. These results show that the fusion of the CBD to animal motors confers Ca(2+)-CaM regulation and suggest that the CBD functions as a modular domain in disrupting motor-MT interaction. Our data also support the hypothesis that CaM-binding kinesins may have evolved by addition of a CBD to a kinesin motor domain.

Animals↗

Structurally homologous binding of plant calmodulin isoforms to the calmodulin-binding domain of vacuolar calcium-ATPase.

The discovery that plants contain multiple calmodulin (CaM) isoforms having variable sequence identity to mammalian CaM has sparked a flurry of new questions regarding the intracellular role of Ca(2+) regulation in plants. To date, the majority of research in this field has focused on the differential enzymatic regulation of various mammalian CaM-dependent enzymes by the different plant CaM isoforms. However, there is comparatively little information on the structural recognition of target enzymes found exclusively in plant cells. Here we have used a variety of spectroscopic techniques, including nuclear magnetic resonance, circular dichroism, and fluorescence spectroscopy, to study the interactions of the most conserved and most divergent CaM isoforms from soybean, SCaM-1, and SCaM-4, respectively, with a synthetic peptide derived from the CaM-binding domain of cauliflower vacuolar calcium-ATPase. Despite their sequence divergence, both SCaM-1 and SCaM-4 interact with the calcium-ATPase peptide in a similar calcium-dependent, stoichiometric manner, adopting an antiparallel binding orientation with an alpha-helical peptide. The single Trp residue is bound in a solvent-inaccessible hydrophobic pocket on the C-terminal domain of either protein. Thermodynamic analysis of these interactions using isothermal titration calorimetry demonstrates that the formation of each calcium-SCaM-calcium-ATPase peptide complex is driven by favorable binding enthalpy and is very similar to the binding of mammalian CaM to the CaM-binding domains of myosin light chain kinases and calmodulin-dependent protein kinase I.

Amino Acid Sequence↗

Structural and immunological characterization of the myosin-like 110-kD subunit of the intestinal microvillar 110K-calmodulin complex: evidence for discrete myosin head and calmodulin-binding domains.

The actin bundle within each microvillus of the intestinal brush border is tethered laterally to the membrane by spirally arranged bridges. These bridges are thought to be composed of a protein complex consisting of a 110-kD subunit and multiple molecules of bound calmodulin (CM). Recent studies indicate that this complex, termed 110K-CM, is myosin-like with respect to its actin binding and ATPase properties. In this study, possible structural similarity between the 110-kD subunit and myosin was examined using two sets of mAbs; one was generated against Acanthamoeba myosin II and the other against the 110-kD subunit of avian 110K-CM. The myosin II mAbs had been shown previously to be cross-reactive with skeletal muscle myosin, with the epitope(s) localized to the 50-kD tryptic fragment of the subfragment-1 (S1) domain. The 110K mAbs (CX 1-5) reacted with the 110-kD subunit as well as with the heavy chain of skeletal but not with that of smooth or brush border myosin. All five of these 110K mAbs reacted with the 25-kD, NH2-terminal tryptic fragment of chicken skeletal S1, which contains the ATP-binding site of myosin. Similar tryptic digestion of 110K-CM revealed that these five mAbs all reacted with a 36-kD fragment of 110K (as well as larger 90- and 54-kD fragments) which by photoaffinity labeling was shown to contain the ATP-binding site(s) of the 110K subunit. CM binding to these same tryptic digests of 110K-CM revealed that only the 90-kD fragment retained both ATP- and CM-binding domains. CM binding was observed to several tryptic fragments of 60, 40, 29, and 18 kD, none of which contain the myosin head epitopes. These results suggest structural similarity between the 110K and myosin S1, including those domains involved in ATP- and actin binding, and provide additional evidence that 110K-CM is a myosin. These studies also support the results of Coluccio and Bretscher (1988. J. Cell Biol. 106:367-373) that the calmodulin-binding site(s) and the myosin head region of the 110-kD subunit lie in discrete functional domains of the molecule.

Acanthamoeba↗

Distinct functions of calmodulin are required for the uptake step of receptor-mediated endocytosis in yeast: the type I myosin Myo5p is one of the calmodulin targets.

The uptake step of receptor-mediated endocytosis in yeast is dependent on the calcium binding protein calmodulin (Cmd1p). In order to understand the role that Cmd1p plays, a search was carried out for possible targets among the genes required for the internalization process. Co-immunoprecipitation, two-hybrid and overlay assays demonstrated that Cmd1p interacts with Myo5p, a type I unconventional myosin. Analysis of the endocytic phenotype and the Cmd1p-Myo5p interaction in thermosensitive cmd1 mutants indicated that the Cmd1p-Myo5p interaction is required for endocytosis in vivo. However, the Cmd1p-Myo5p interaction requirement was partially overcome by deleting the calmodulin binding sites (IQ motifs) from Myo5p, suggesting that these motifs inhibit Myo5p function. Additionally, genetic and biochemical evidence obtained with a collection of cmd1 mutant alleles strongly suggests that Cmd1p plays an additional role in the internalization step of receptor-mediated endocytosis in yeast.

Amino Acid Sequence↗

Peptides related to the calcium binding domains II and III of calmodulin. Synthesis and calmodulin-like features.

Three hexadecapeptides which correspond to the putative Ca2+ binding domains II and III of calmodulin were synthesized employing solid phase methodology. One of the peptides contained an internal cystine bridge which was formed while the corresponding linear peptide was still attached to the polymeric carrier. The interaction of the synthetic peptides with calcium ions was investigated using Tb3+-mediated fluorescence. Binding was of the order Ca12 greater than Ca13 greater than Ca13C (Fig. 1) with binding constants KTb3+ = 0.68 X 10(-5), 0.54 X 10(-5), and 0.21 X 10(-5) M-1 respectively. Biological activity of the compounds was assessed by measuring their stimulatory effect on erythrocyte membrane (Ca2+ + Mg2+)-ATPase activity. For 50% activity as compared with CaM, the concentration of peptides required was for Ca12, Ca13 and Ca13C, 50, 100 and 167 times higher than CaM, respectively. The results suggest that the three synthetic peptides possess certain calmodulin-like features.

Binding Sites↗

Calmodulin kinase and a calmodulin-binding 'IQ' domain facilitate L-type Ca2+ current in rabbit ventricular myocytes by a common mechanism.

1. Ca2+-calmodulin-dependent protein kinase II (CaMK) and a calmodulin (CaM)-binding 'IQ' domain (IQ) are both implicated in Ca2+-dependent regulation of L-type Ca2+ current (I(Ca)). We used an IQ-mimetic peptide (IQmp), under conditions in which CaMK activity was controlled, to test the relationship between these CaM-activated signalling elements in the regulation of L-type Ca2+ channels (LTCCs) and I(Ca) in rabbit ventricular myocytes. 2. A specific CaMK inhibitory peptide nearly abolished I(Ca) facilitation, but the facilitation was 'rescued' by cell dialysis with IQmp. 3. IQmp significantly enhanced I(Ca) facilitation and slowed the fast component of I(Ca) inactivation, compared with an inactive control peptide. Neither effect could be elicited by a more avid CaM-binding peptide, suggesting that generalized CaM buffering did not account for the effects of IQmp. 4. I(Ca) facilitation was abolished and the fast component of inactivation eliminated by ryanodine, caffeine or thapsigargin, suggesting that the sarcoplasmic reticulum (SR) is an important source of Ca2+ for I(Ca) facilitation and inactivation. IQmp did not restore I(Ca) facilitation under these conditions. 5. Engineered Ca2+-independent CaMK and IQmp each markedly increased LTCC open probability (P(o)) in excised cell membrane patches. The LTCC P(o) increases with CaMK and IQmp were non-additive, suggesting that CaMK and IQmp are components of a shared signalling pathway. 6. Both CaMK and IQmp induced a modal gating shift in LTCCs that favoured prolonged openings, indicating that CaMK and IQmp affect LTCCs through a common biophysical mechanism. 7. These findings support the hypothesis that CaMK is required for physiological I(Ca) facilitation in cardiac myocytes. Both CaMK and IQmp were able to induce a modal gating shift in LTCCs, suggesting that each of these signalling elements is important for Ca2+-CaM-dependent LTCC facilitation in cardiac myocytes.

Algorithms↗

Effects of aging and morphine administration on calmodulin and calmodulin-regulated enzymes in striata of mice.

Male ICR mice, young (25-days old), mature (3-months old), and old (22 months), were injected with morphine sulfate (10 mg/kg, s.c.) or were implanted with morphine pellets (75 mg). Controls received saline injections or placebo pellets. One hour after injections and 72 h after pellet implantations, the mice were decapitated and striatal regions were removed for the following analyses: calmodulin (CaM) levels via radioimmunoassay and activities of cyclic nucleotide phosphodiesterases, adenylate and guanylate cyclases, and Ca2+, Mg2+-ATPase. Acute morphine treatment produced the following: (1) increases in calmodulin levels in the young and old mice while having no effect on mature levels; (2) increases in activities of guanylate cyclase of mature mice while decreasing those of the old mice; (3) no effects on activity of adenylate cyclase; (4) decreased activity of cyclic AMP-phosphodiesterase in young mice only; (5) decreased activity of Ca2+, Mg2+-ATPase in the old mice only. The only changes found in striata from morphine-tolerant mice when compared with age-matched controls were elevations in cyclic GMP-phosphodiesterase activities in all three age groups. Differences in control values of the three age groups were as follows: CaM levels, mature greater than old greater than young; Ca2+, Mg2+-ATPase activity, old greater than mature-young. The results indicate age-induced changes in cellular regulation and biochemical responses to morphine.

3',5'-Cyclic-AMP Phosphodiesterases↗

Calmodulin inhibitors decrease the CRF-and AVP-induced ACTH release in vitro: interaction of calcium-calmodulin and the cyclic AMP system.

The effect of N-(6-aminohexyl)-5-chloro-naphthalene-1-sulfomide (W-7) and trifluoperazine (TFP) was examined on ACTH release from cultured rat anterior pituitary cells and pituitary halves. These drugs significantly inhibited the ACTH release induced by synthetic ovine corticotropin-releasing factor (CRF) in a dose-related manner. In pituitary halves, arginine vasopressin (AVP) at 10 and 100 ng/ml showed almost the same ACTH-releasing activity as CRF at the same concentrations. W-7 and TFP inhibited the CRF-and AVP-induced ACTH release from pituitary halves. The cyclic AMP levels in the pituitary halves were significantly increased by CRF, but not AVP. Although W-7 inhibited CRF-induced ACTH release, it did not have an effect in cyclic AMP accumulation. These results suggest that CRF exerts ACTH-releasing activity through both the calcium-calmodulin system and cyclic AMP system and that AVP stimulates ACTH release mainly through the calcium-calmodulin system.

Adrenocorticotropic Hormone↗

Dynamic redistribution of calmodulin in HeLa cells during cell division as revealed by a GFP-calmodulin fusion protein technique.

It has been suggested by many studies that Ca2+ signaling plays an important role in regulating key steps in cell division. In order to study the down stream components of calcium signaling, we have fused the gene of calmodulin (CaM) with that of green fluorescent protein (GFP) and expressed it in HeLa cells. The GFP-CaM protein was found to have similar biochemical properties as the wild-type CaM, and its distribution was also similar to that of the endogenous CaM. Using this GFP-tagged CaM as a probe, we have conducted a detailed examination of the spatial- and temporal-dependent redistribution of calmodulin in living mammalian cells during cell division. Our major findings are: (1) high density of CaM was found to distribute in two sub-cellular locations during mitosis; one fraction was concentrated in the spindle poles, while the other was concentrated in the sub-membrane region around the cell. (2) The sub-membrane fraction of CaM became aggregated at the equatorial region where the cleavage furrow was about to form. The timing of this localized aggregation of CaM was closely associated with the onset of cytokinesis. (3) Using a TA-CaM probe, we found that the sub-membrane fraction of CaM near the cleavage furrow was selectively activated during cell division. (4) When we injected a CaM-specific inhibitory peptide into early anaphase cells, cytokinesis was either blocked or severely delayed. These findings suggest that, in addition to Ca2+ ion, CaM may represent a second signal that can also play an active role in determining the positioning and timing of the cleavage furrow formation.

Calmodulin↗

Comparison of characterization among Bordetella calmodulin-like protein, bovine brain calmodulin and Escherichia coli acyl-carrier protein.

We previously reported that Bordetella calmodulin-like protein (CLP), like bovine brain calmodulin (CaM), enhances adenylate cyclase and phosphodiesterase activities. In this communication, antigenic and biochemical characters were compared between CLP and CaM. It was found that anti-CLP and anti-CaM sera obtained reacted with CaM and CLP, respectively. The amino acid composition of CLP was similar to CaM. The similarity was also found in an Escherichia coli acyl-carrier protein (ACP), a Ca(2+)-binding protein. Though the amino acid sequence of N-terminus region of CLP has no significant homology with CaM, ACP has highly homology in its N-terminus similar to CaM. These results suggest that CLP might act as a Ca(2+)-binding protein, and/or an ACP during the activation of adenylate cyclase and phosphodiesterase.

Acyl Carrier Protein↗

Expression of calmodulin-binding domain of neuronal nitric synthase and its binding activity to calmodulin.

To facilitate the study of associations of nNOS functions with its calmodulin (CaM) binding domain and to prepare nNOS specific inhibiting peptides from phage peptide library, we have amplified the coding gene of nNOS CaM-binding domain (nNOS 2544-2988 bp) and expressed it in E.coli. The recombinant product in the size of 22 kDa was purified (over 90% in pure) by His.Tag-Sepharose column and its obvious CaM-binding activity was detected with CaM overlay assay. Since it possesses the sequence specificity and effective calmodulin-binding activity, the protein was considered an ideal target for screening nNOS specific peptides from peptide library and also an antigen for marking nNOS antibody.

Binding Sites↗

Dependence of Na+/H+ antiport activation in cultured rat aortic smooth muscle on calmodulin, calcium, and ATP. Evidence for the involvement of calmodulin-dependent kinases.

The role of Ca2+/calmodulin-dependent processes in the activation of the Na+/H+ antiport of primary cultures of rat aortic smooth muscle was studied using 22Na+ uptake and measurement of intracellular pH (pHi) with the fluorescent pH dye 2',7'-bis-(2-carboxyethyl)-5(and 6)-carboxyfluorescein. Antiport activation following exposure to serum and by the induction of an intracellular acidosis could be markedly attenuated by calmodulin antagonists. Ionomycin also transiently elevated pHi and 5-(N-ethyl-N-isopropyl) amiloride-sensitive 22Na+ influx, effects consistent with activation of the antiport; these effects were abolished in cells exposed to calmodulin antagonists or [ethylenebis(oxyethylenenitrilo)]tetraacetic acid. Activation of the antiport following intracellular acidosis was markedly affected by cellular ATP depletion. A comparison of the abilities of control and 2-deoxy-D-glucose-treated cells to increase 5-(N-ethyl-N-isopropyl)amiloride-sensitive 22Na+ influx in response to graded acidifications indicated that attenuation of Na+/H+ antiport activity was due to both a shift of its pHi dependence and to a reduction in maximal activity. The results suggest that the Na+/H+ antiport of rat aortic smooth muscle is dependent on Ca2+/calmodulin-dependent processes, presumably phosphorylation, which influences its activity by modulating (i) an intracellular proton dependent regulatory mechanism (allosteric site) and (ii) the maximum activity of the antiport.

Adenosine Triphosphate↗

Interaction of Bordetella pertussis adenylate cyclase with calmodulin. Identification of two separated calmodulin-binding domains.

The structural organization of Bordetella pertussis adenylate cyclase was examined by limited proteolysis with trypsin and/or cross-linking with azido-calmodulin a photoactivable derivative of its activator, calmodulin (CaM). Adenylate cyclase (which consists of three structurally related peptides of 50, 45, and 43 kDa as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) formed a 1:1 complex with CaM or azido-CaM. CaM-bound adenylate cyclase was cleaved by trypsin into two separate trypsin-resistant fragments of 25 and 18 kDa which both interacted with CaM as judged by their ability to be cross-linked with azido-CaM. These two fragments remained associated with CaM in a catalytically active conformation resembling that of the undigested complex. When proteolysis was carried out in the absence of CaM, the adenylate cyclase was completely inactivated in less than 3 min. Sodium dodecyl sulfate-polyacrylamide gel revealed a single 24-kDa trypsin-resistant fragment. Since this fragment cannot be cross-linked with azido-CaM we suggest that the CaM-binding site on the 25-kDa moiety of the adenylate cyclase is located on a short segment of 1 kDa.

Adenylyl Cyclases↗

Hydrophobic interaction of the Ca2+-calmodulin complex with calmodulin antagonists. Naphthalenesulfonamide derivatives.

Calmodulin antagonists such as N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), which bind to calmodulin (CaM) in the presence of Ca2+ and selectively inhibit CaM-induced enzyme activation, contain a hydrophobic moiety. In this study, the naphthalenesulfonamide derivatives that lacked the chlorine molecule were less hydrophobic than those with chlorine. The chlorine-deficient derivatives also were less able to suppress the fluorescence of the hydrophobic probe (2-p-toluidinylnaphthalene-6-sulfonate) in the presence of the Ca2+-CaM complex. The affinity of naphthalenesulfonamides for Ca2+-CaM correlated well with their hydrophobicity and their potency in inhibiting Ca2+-CaM-dependent enzymes such as Ca2+-dependent cyclic nucleotide phosphodiesterase. The correlation between their hydrophobicity and affinity for the Ca2+-CaM complex also was observed when derivatives with various lengths of alkyl chain were used and when bromine, fluorine, or cyanogen was substituted for chlorine. Our observations suggest that these CaM antagonists may bind to the Ca2+-CaM complex through a hydrophobic interaction.

Animals↗

Involvement of calmodulin in granulocyte chemotaxis: the effect of calmodulin inhibitors.

Chemotaxis and locomotion in rabbit peritoneal granulocytes are strongly inhibited by trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), both known as calmodulin inhibitors. This inhibition occurs in a concentration range where cell damage is not significant. Although inhibition was most pronounced in experiments with Ca2+ and Mg2+ present in the medium, inhibition of chemotaxis by trifluoperazine and W-7 was also observed in the absence of these ions. The results suggest that calmodulin is involved in granulocyte chemotaxis and locomotion.

Animals↗

Role of domain 3 of calmodulin in activation of calmodulin-stimulated phosphodiesterase and smooth muscle myosin light chain kinase.

CaM[3 TnC] is a calmodulin-cardiac troponin C chimeric protein containing the first, second, and fourth calcium-binding domains of calmodulin (CaM) and the third calcium-binding domain of cardiac troponin C (cTnC) (George, S. E., Su, Z., Fan, D., and Means, A. R. (1993) J. Biol. Chem. 268, 25213-25220). CaM[3 TnC] shows altered activation of phosphodiesterase (PDE) and is a potent competitive inhibitor of smooth muscle myosin light chain kinase (smMLCK) activation by CaM. To determine why CaM[3 TnC] exhibits altered target enzyme interactions, we constructed a series of domain 3 CaM mutants. We began with subdomain substitutions, replacing most of CaM's helix 5, Ca2+ binding loop 3, and helix 6 with the corresponding subdomains of cTnC. Only CaM[helix 6-TnC] exhibited significant impairment of smMLCK and PDE activation. We then individually substituted the residues in the region of CaM's helix 6 with the corresponding cTnC residue. This revealed that CaM residues Thr-110, Leu-112, and Lys-115 were critical for full smMLCK activation and could not be substituted by the corresponding cTnC residue (Gln, Thr, and Thr, respectively). In contrast, only the L112T substitution significantly affected PDE activation. The CaM-smMLCK peptide structure (Meador, W. E., Means, A. R., and Quiocho, F. A. (1992) Science 257, 1251-1255) suggests a relationship between the proposed helix 6 smMLCK-activating residues and those previously described in helix 2 (VanBerkum, M. F. A., and Means, A. R. (1991) J. Biol. Chem. 266, 21488-21495).

3',5'-Cyclic-AMP Phosphodiesterases↗

Characterization of novel calmodulin-binding peptides with distinct inhibitory effects on calmodulin-dependent enzymes.

We describe the isolation and interaction with calmodulin (CaM) of two 10-amino-acid peptides (termed peptides 1 and 2; AWDTVRISFG and AWPSLQAIRG respectively) derived from a phage random peptide display library. Both peptides are shorter than previously described CaM-binding peptides and lack certain features found in the sequences of CaM-binding domains present in CaM-activated enzymes. However, 1H NMR spectroscopy and fluorimetry indicate that both peptides interact with CaM in the presence of Ca2+. The two peptides differentially inhibited CaM-dependent kinases I and II (CaM kinases I and II) but did not affect CaM-dependent phosphodiesterase. Peptide 1 inhibited CaM kinase I but not CaM kinase II, whereas peptide 2 inhibited CaM kinase II, but only partially inhibited CaM kinase I at a more than 10-fold higher concentration. Peptide 1 also inhibited a plant calcium-dependent protein kinase, whereas peptide 2 did not. The ability of peptides 1 and 2 to differentially inhibit CaM-dependent kinases and CaM-dependent phosphodiesterase suggests that they may bind to distinct regions of CaM that are specifically responsible for activation of different CaM-dependent enzymes.

Animals↗