Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.17 (CaMKII)
 4,029 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous studies have shown that activators of protein kinase C (C kinase) produce synaptic potentiation in the hippocampus. For example, the C kinase activator phorbol dibutyrate has been shown to increase transmitter release in the hippocampus. In addition, a role for C kinase in long-term potentiation has been proposed. A common assumption in such studies has been that substrates for C kinase were responsible for producing these forms of synaptic potentiation. However, we have recently shown that phorbol dibutyrate increased the phosphorylated of synapsin II (formerly protein III, Browning et al., 1987) in chromaffin cells (Haycock et al., 1988). Synapsin II is a synaptic vesicle-associated phosphoprotein that is a very poor substrate for C kinase but an excellent substrate for cAMP-dependent and Ca2+/calmodulin-dependent protein kinase. We felt, therefore, that activation of C kinase might lead to activation of a kinase cascade. Thus effects of C kinase activation might be produced via the phosphorylation of proteins that are not substrates for C kinase. In this report we test the hypothesis that activators of C kinase increase the phosphorylation of synapsin II and an homologous protein synapsin I. Our data indicate that PdBu produced dose-dependent increases in the phosphorylation of synapsin I and synapsin II. We also performed phospho-site analysis of synapsin I using limited proteolysis. These studies indicated that PdBu increased the phosphorylation of multiple sites on synapsin I. These sites have previously been shown to be phosphorylated by both cAMP-dependent protein kinase and the multifunctional Ca2+/calmodulin-dependent protein kinase II.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Activators of protein kinase C increase the phosphorylation of the synapsins at sites phosphorylated by cAMP-dependent and Ca2+/calmodulin-dependent protein kinase in the rat hippocampal slice. 131 Nov 30

Synapsin I is a synaptic vesicle-specific phosphoprotein which is able to bind and bundle actin filaments in a phosphorylation-dependent fashion. In the present paper we have analyzed the effects of synapsin I on the kinetics of actin polymerization and their modulation by site-specific phosphorylation of synapsin I. We found that dephosphorylated synapsin I accelerates the initial rate of actin polymerization and decreases the rate of filament elongation. The effect was observed at both low and high ionic strength, was specific for synapsin I, and was still present when polymerization was triggered by F-actin seeds. Dephosphorylated synapsin I was also able to induce actin polymerization and bundle formation in the absence of KCl and MgCl2. The effects of synapsin I were strongly decreased after its phosphorylation by Ca2+/calmodulin-dependent protein kinase II. These observations suggest that synapsin I has a phosphorylation-dependent nucleating effect on actin polymerization. The data are compatible with the view that changes in the phosphorylation state of synapsin I play a functional role in regulating the interactions between the nerve terminal cytoskeleton and synaptic vesicles in various stages of the exoendocytotic cycle.
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PMID:Effects of the neuronal phosphoprotein synapsin I on actin polymerization. I. Evidence for a phosphorylation-dependent nucleating effect. 131 63

Two Ca(2+)-calmodulin (CaM)-dependent protein kinases were purified from rat brain using as substrate a synthetic peptide based on site 1 (site 1 peptide) of the synaptic vesicle-associated protein, synapsin I. One of the purified enzymes was an approximately 89% pure protein of M(r) = 43,000 which bound CaM in a Ca(2+)-dependent fashion. The other purified enzyme was an apparently homogenous protein of M(r) = 39,000 accompanied by a small amount of a M(r) = 37,000 form which may represent a proteolytic product of the 39-kDa enzyme. The 39-kDa protein bound CaM in a Ca(2+)-dependent fashion. Gel filtration analysis indicated that both enzymes are monomers. The 43- and 39-kDa enzymes are named Ca(2+)-CaM-dependent protein kinases Ia and Ib (CaM kinases Ia, Ib), respectively. The specific activities of CaM kinases Ia and Ib were similar (5-8 mumol/min/mg protein). CaM kinase Ia (but not CaM kinase Ib) activity was enhanced by addition of a CaM-Sepharose column wash (non-binding) fraction suggesting the existence of an "activator" of CaM kinase Ia. Both kinases phosphorylated exogenous substrates (site 1 peptide and synapsin I) in a Ca(2+)-CaM-dependent fashion and both kinases underwent autophosphorylation. CaM kinase Ia autophosphorylation was Ca(2+)-CaM-dependent and occurred exclusively on threonine while CaM kinase Ib autophosphorylation showed Ca(2+)-CaM independence and occurred on both serine and threonine. Proteolytic digestion of autophosphorylated CaM kinases Ia and Ib yielded phosphopeptides of differing M(r). These characteristics, as well as enzymatic and regulatory properties (DeRemer, M. F., Saeli, R. J. Brautigen, D. L., and Edelman, A. M. (1992) J. Biol. Chem. 267, 13466-13471), indicate that CaM kinases Ia and Ib are distinct and possibly previously unrecognized enzymes.
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PMID:Ca(2+)-calmodulin-dependent protein kinases Ia and Ib from rat brain I. Identification, purification, and structural comparisons. 132 21

In addition to physical properties (DeRemer, M. F., Saeli, R. J., and Edelman, A. M. (1992) J. Biol. Chem. 267, 13460-13465), enzymatic and regulatory characteristics indicate that calmodulin (CaM) kinase Ia and CaM kinase Ib are distinct entities. The Km values for ATP and site 1 peptide were similar between the two kinases, however, CaM kinase Ib is approximately 20-fold more sensitive to CaM than is CaM kinase Ia. The kinases also displayed differential sensitivities to divalent metal ions. For both kinases, site 1 peptide, synapsin I, and syntide-2 were highly preferred substrates relative to others tested. A 72-kDa protein from a heat-treated extract of rat pancreas was phosphorylated by CaM kinase Ib but not by CaM kinase Ia. CaM kinase Ia activity displayed a pronounced lag in its time course suggesting enzyme activation over time. Preincubation of CaM kinase Ia in the combined presence of Ca(2+)-CaM and MgATP led to a time-dependent increase in its site 1 peptide kinase activity of up to 15-fold. The extent of activation of CaM kinase Ia correlated with the extent of autophosphorylation. The enzyme retained full Ca(2+)-CaM dependence in the activated state which was rapidly reversible by treatment with protein phosphatase 2A catalytic subunit. Thus, the activation of CaM kinase Ia is a result of its Ca(2+)-CaM-dependent autophosphorylation. CaM kinase Ib was not activated by preincubation under autophosphorylating conditions yet lost approximately 90% of its activity toward either an exogenous substrate (site 1 peptide) or itself (autophosphorylation) after incubation with protein phosphatase 2A catalytic subunit. The deactivated state was not reversed by subsequent incubations under autophosphorylating conditions. Thus, CaM kinase Ib activity is dependent upon phosphorylation by a regulating kinase(s) which is resolved from CaM kinase Ib during purification of the latter.
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PMID:Ca(2+)-calmodulin-dependent protein kinases Ia and Ib from rat brain. II. Enzymatic characteristics and regulation of activities by phosphorylation and dephosphorylation. 132 22

Widespread localization, responsiveness to numerous signal transduction systems, and broad substrate specificity enable the multifunctional CaM kinase to mediate regulation of many cellular functions. The abundance and diversity of CaM kinase substrates attest to its role as a multifunctional kinase. However, expanded identification of its in situ substrates as well as the consequences of their regulation by phosphorylation needs to be accomplished. Recently identified substrates have contributed to the list of potential functions for the CaM kinase. CREB is a hormonally stimulated transcriptional activator, and CaM kinase may lie on the pathway to its activation. This pathway could provide an interface between the potentiation of Ca2+ signals by CaM kinase and longer-term modifications of neuronal gene expression. The ryanodine receptor, as well as phospholamban, are involved in cardiac Ca2+ homeostasis, and their regulation by CaM kinase phosphorylation suggests the possibility of some feedback control of intracellular Ca2+ levels by CaM kinase. Regulation of neuronal plasticity by phosphorylation of synapsin I and of postsynaptic substrates necessary for long-term potentiation is another dynamic area of investigation. The study of substrates and their functions promises to continue providing exciting insights into the control of cellular signalling by Ca2+. Molecular cloning has enabled structural comparison of neuronal isoforms of the kinase, and has revealed the existence of closely related subunits. Subunits identified to data differ substantially only in two small variable domains, yet their expression in various tissues and during the course of development is precisely controlled. What unique properties do these small variable domains impart to the different isoforms? What directs high concentrations of kinase to a particular subcellular localization, and especially to the PSD? Further molecular cloning will undoubtedly determine whether other multifunctional CaM kinases with unique structures and properties exist. Finally, studies on the autoregulatory properties of CaM kinase have provided a fascinating picture of how this molecule can alone encode responses to Ca2+ signals, potentiating both the duration and magnitude of its activity. Autophosphorylation of the Thr286 autonomy site both traps calmodulin and permits Ca(2+)-independent activity after calmodulin dissociates. Further analysis of the role of the holoenzyme structure in these modulations will help clarify remaining mechanistic questions. Studies performed during the past few years have clearly established that this Ca(2+)-independent activity is generated in situ in response to a variety of cell stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Neuronal Ca2+/calmodulin-dependent protein kinases. 132 38

Synapsin I is a synaptic vesicle-associated phosphoprotein that is involved in the modulation of neurotransmitter release. Ca2+/calmodulin-dependent protein kinase II, which phosphorylates two sites in the carboxy-terminal region of synapsin I, causes synapsin I to dissociate from synaptic vesicles and increases neurotransmitter release. Conversely, the dephosphorylated form of synapsin I, but not the form phosphorylated by Ca2+/calmodulin-dependent protein kinase II, inhibits neurotransmitter release. The amino-terminal region of synapsin I interacts with membrane phospholipids, whereas the C-terminal region binds to a protein component of synaptic vesicles. Here we demonstrate that the binding of the C-terminal region of synapsin I involves the regulatory domain of a synaptic vesicle-associated form of Ca2+/calmodulin-dependent protein kinase II. Our results indicate that this form of the kinase functions both as a binding protein for synapsin I, and as an enzyme that phosphorylates synapsin I and promotes its dissociation from the vesicles.
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PMID:Synaptic vesicle-associated Ca2+/calmodulin-dependent protein kinase II is a binding protein for synapsin I. 132 83

The ATP.Mg-dependent protein phosphatase activating factor (FA) has been identified and purified to near homogeneity from brain. In this report, as evidenced on SDS-polyacrylamide gel electrophoresis followed by autoradiography, factor FA has further been identified as a cAMP and Ca(2+)-independent brain kinase that could phosphorylate synapsin I, a neuronal protein that coats synaptic vesicles, binds to cytoskeleton, and is believed to be involved in the modulation of neurotransmission. Kinetic study further indicated that factor FA could phosphorylate synapsin I with a low Km value of about 2 microM and with a molar ratio of 1 mol of phosphate per mole of protein. Peptide mapping analysis revealed that factor FA specifically phosphorylated the tail region of synapsin I but on a unique site distinct from those phosphorylated by Ca2+/calmodulin-dependent protein kinase II and cAMP-dependent protein kinase, the two well-established synapsin I kinases. Functional study further revealed that factor FA could phosphorylate this unique specific site on the tail region of synapsin I and thereby inhibit cross-linking of synapsin I with microtubules. The results further suggest the possible involvement of factor FA as a synapsin I kinase in the regulation of axonal transport process of synaptic vesicles via the promotion of vesicles motility during neurotransmission.
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PMID:Identification of the ATP.Mg-dependent protein phosphatase activator (FA) as a synapsin I kinase that inhibits cross-linking of synapsin I with brain microtubules. 133 16

Introduction of the dephosphorylated from of synapsin I into rat brain synaptosomes using freeze-thaw (transient) permeabilization significantly decreased the K(+)-induced release of glutamate. In contrast, introduction of synapsin I that had been phosphorylated by Ca2+/calmodulin-dependent protein kinase II was without effect on glutamate release. Addition of dephosphosynapsin I after freeze-thaw treatment also had no effect. Thus, the action of synapsin I was dependent on the phosphorylation state of synapsin I and on its entry into the synaptosomes. Our results implicate synapsin I as an important component in the regulation of neurotransmitter release in the mammalian nervous system.
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PMID:Synapsin I regulates glutamate release from rat brain synaptosomes. 134 42

In cultured rat hippocampal neurons, glutamate elevated the Ca(2+)-independent activity of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) through autophosphorylation when the neurons were incubated in Mg(2+)-free buffer, and this response was blocked by specific antagonists of the N-methyl-D-aspartate (NMDA) receptor. In addition, glutamate stimulated the transient translocation of protein kinase C (PKC) from the cytosol to the membrane fraction. This effect was not blocked by NMDA receptor antagonists but was partially blocked by DL-2-amino-3-phosphonopropionate. Quisqualate or trans-1-amoinocyclopentane-trans1,3-dicarboxylate produced a similar effect on the translocation of PKC. In the experiments with 32P-labeled cells, the phosphorylation of microtuble-associated protein 2 and synapsin I, as well as autophosphorylation of CaM kinase II, were found to be stimulated by exposure to glutamate. These results suggest that glutamate can activate CaM kinase II through the ionotropic NMDA receptor, which in turn increases the phosphorylation of microtuble-associated protein 2 and synapsin I. PKC was activated through the metabotropic glutamate receptor in the hippocampal neurons.
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PMID:Activation of Ca2+/calmodulin-dependent protein kinase II and protein kinase C by glutamate in cultured rat hippocampal neurons. 135 79

Characteristics of the autophosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) from the cytosol and in the postsynaptic densities (PSD) of rat brain were investigated. Several proteins were surveyed for their abilities to serve as a substrate for non-autophosphorylated and autophosphorylated CaM kinase IIs from the cytosol and PSD. The tested substrates were separated into two groups. Autophosphorylation of the kinase slightly decreased or did not change its activities towards substrates of the first group: myosin light chain of chicken gizzard, synapsin I, tau factor and microtubule-associated protein 2. In contrast, autophosphorylation of the enzyme increased its activities towards substrates of the second group: syntide-2, histone H1, calcineurin and myelin basic protein. The Ca2+/calmodulin-independent kinase activity increased by autophosphorylation with any of substrates tested. Similar results were obtained with the cytosolic and PSD CaM kinase II. Trifluoperazine and mastoparan, calmodulin binding antagonists, inhibited the activity of the non-autophosphorylated CaM kinase II, but had no effect or only a slight inhibitory effect on the activity of the autophosphorylated CaM kinase II, indicating that the autophosphorylated kinase has no requirement for calmodulin for Ca(2+)-dependent activity and/or a higher affinity for calmodulin The results suggest that the autophosphorylation of CaM kinase II is a subtle mechanism for regulating the interaction between the enzyme and substrate.
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PMID:Autophosphorylation of Ca2+/calmodulin-dependent protein kinase II: effects on interaction between enzyme and substrate. 164 40


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