Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Light-dependent deactivation of rhodopsin as well as homologous desensitization of beta-adrenergic receptors involves receptor phosphorylation that is mediated by the highly specific protein kinases rhodopsin kinase (RK) and beta-adrenergic receptor kinase (beta ARK), respectively. We report here the cloning of a complementary DNA for RK. The deduced amino acid sequence shows a high degree of homology to beta ARK. In a phylogenetic tree constructed by comparing the catalytic domains of several protein kinases, RK and beta ARK are located on a branch close to, but separate from the cyclic nucleotide-dependent protein kinase and protein kinase C subfamilies. From the common structural features we conclude that both RK and beta ARK are members of a newly delineated gene family of guanine nucleotide-binding protein (G protein)-coupled receptor kinases that may function in diverse pathways to regulate the function of such receptors.
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PMID:The receptor kinase family: primary structure of rhodopsin kinase reveals similarities to the beta-adrenergic receptor kinase. 165 54

The possibility that protein kinase C is involved in phototransduction by phosphorylating rhodopsin was explored in situ and in vitro. Pretreatment of intact retinas with phorbol myristate acetate markedly increased the light-dependent phosphorylation of rhodopsin, with the greatest effects observed at lower light levels. Phorbol myristate acetate treatment did not affect rhodopsin phosphorylation in retinas not exposed to light, suggesting that protein kinase C modulates the phosphorylation state of rhodopsin in a light-dependent manner. Limited proteolysis of rhodopsin phosphorylated in situ indicates that protein kinase C modifies rhodopsin on a domain distinct from that recognized by rhodopsin kinase. In vitro, protein kinase C purified from bovine retinas phosphorylated unbleached and bleached rhodopsin. Our results are consistent with protein kinase C phosphorylating unbleached rhodopsin in response to low light, suggesting that protein kinase C plays a role in light adaptation.
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PMID:Involvement of protein kinase C in the phosphorylation of rhodopsin. 191 16

Addition of protein kinase C activators to electropermeabilized frog rod photoreceptors enhances the phosphorylation of proteins with molecular masses of 54, 24, 19, 17, 12, and 11 kDa. The latter two correspond to components I and II, which are also phosphorylated by cyclic nucleotide-dependent protein kinase. Stimulation of phosphorylation by the protein kinase C activator oleoylacetylglycerol (OAG) is half-maximal at 7.7 microM OAG and is reduced by the protein kinase C inhibitor H-7. In contrast with earlier observations, no effects of calcium, calmodulin, or insulin on protein phosphorylations are observed. We find evidence for only three protein kinases in rod outer segments: a protein kinase C-like activity, cAMP-dependent protein kinase, and rhodopsin kinase. With the exception of components I and II, the substrate proteins for each kinase are distinct. Treatment of intact rods with OAG decreases the amplitude of the photoresponse and dark levels of cGMP up to 40%, as well as depressing the light-stimulated decrease in cGMP levels. These effects are observed between 0.1 and 1 microM OAG. The data suggest that OAG-sensitive reactions may modulate pathways that support the light response.
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PMID:Stimulation of protein phosphorylations in frog rod outer segments by protein kinase activators. Suppression of light-induced changes in membrane current and cGMP by protein kinase C activators. 254 93

Rod outer segments (ROS) from bovine retinae were found to have high levels of calcium/phospholipid dependent protein kinase (protein kinase C). Protein kinase C behaves as an extrinsic membrane protein and phosphorylates rhodopsin in a calcium-dependent manner. The abundance of protein kinase C in ROS is similar to that of rhodopsin kinase. Its ability to phosphorylate rhodopsin in ROS membranes suggests protein kinase C may play an important role in the regulation of signal transduction in the ROS. The limited set of extrinsic membrane proteins and abundance of protein kinase C makes this tissue an extremely useful source to purify protein kinase C. The extrinsic membrane protein fraction has 6-7 U protein kinase C activity per mg protein, and the enzyme is quite stable apparently due to the lack of proteases in the preparation. A procedure was developed using phosphatidylserine- and calcium-dependent binding of protein kinase C to phenyl-Sepharose in low ionic strength buffer to resolve protein kinase C and other calcium-binding proteins from the majority of extrinsic membrane proteins. Protein kinase C was eluted using EGTA, and peak fractions directly loaded onto a DEAE-cellulose column. The protein kinase C peak eluted from the ion-exchange column was pooled and had a specific activity greater than 1,000 nmol phosphate transferred to histone per min per mg protein with a recovery of 25 percent of the starting activity. The procedure to purify protein kinase C from ROS is simple and can be completed in one day.
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PMID:Purification of protein kinase C from bovine rod outer segments. 300 71

Calium/phospholipid-dependent protein kinase (protein kinase C) was purified from bovine retinae rod outer segments (ROS). In the presence of 0.1-2 microM calcium protein kinase C binds tightly to ROS and phosphorylates rhodopsin in the absence or presence of illumination. This property of protein kinase C contrasts with that of rhodopsin kinase, which in vitro phosphorylates only bleached rhodopsin. Peptide maps of rhodopsin phosphorylated by protein kinase C or rhodopsin kinase were compared using limited Staphylococcus aureus V8 protease digestion or complete tryptic digestion. Phosphorylation sites map to serine and threonine residues on the cytoplasmic carboxylterminal domain of rhodopsin for both kinases. The functional consequence of protein kinase C phosphorylation of rhodopsin was a reduced ability to stimulate the light-dependent rhodopsin activation of [35S]guanosine 5'-O-(thiotriphosphate) binding to transducin, the GTP-binding regulatory protein present in ROS. Properties of the calcium-stimulated interaction of protein kinase C with membranes and in vitro phosphorylation of intrinsic proteins are discussed based upon the findings.
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PMID:Phosphorylation of rhodopsin by protein kinase C in vitro. 300 75

Mounting evidence suggests that the physiological function of the various subtypes of adrenergic receptors is controlled by phosphorylation/dephosphorylation reactions. It seems intuitively unlikely that this phenomenon will be limited simply to the adrenergic receptors, since these receptors share transmembrane signaling pathways with a host of other plasma membrane receptors. Different types of kinases appear to be involved. On the one hand, phosphorylation reactions may operate in a classical feedback regulatory sense. Thus, the cAMP-dependent protein kinase, once activated by a beta-agonist, can feedback-regulate the function of the receptors by phosphorylating and desensitizing them. Similarly, protein kinase C appears to be able to feedback-regulate the function of alpha 1-adrenergic receptors by phosphorylation. There may also be "cross talk" between the systems. Thus, protein kinase C, when stimulated by phorbols, is able to phosphorylate and desensitize the beta-adrenergic receptors. Moreover, very recently we have found that the cAMP-dependent protein kinase can phosphorylate the alpha 1-adrenergic receptors in vitro. These are examples of one transmembrane signaling system regulating the function of another. Perhaps most interestingly, it appears that there may be a previously unappreciated class of receptor kinases in the cytosol of cells. The first of these, which we have recently found and named beta-ARK, serves to phosphorylate only the agonist-occupied form of the beta-adrenergic receptor. As noted, it is somewhat analogous to the rhodopsin kinase. Such highly specific receptor kinases, which can phosphorylate only the agonist-occupied form of a receptor, represent a potentially elegant mechanism for controlling the function of receptors in a fashion which is linked to their physiological stimulation. How widespread such kinases are, and the actual roles which they play in regulating receptor function, remain to be determined. Finally, it should be stressed that although this review has focused on the regulatory role of receptor phosphorylation, it is by no means our intent to suggest that receptors are the only locus for physiological control of sensitivity to hormone and drug reaction. There is already evidence that guanine nucleotide regulatory proteins can be regulated, and it seems likely that each of the components of the system, including the adenylate cyclase, are likely to be involved in various forms of complex regulation. To date, however, the receptors represent that component of the system whose regulation we understand in the greatest detail.
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PMID:Regulation of adrenergic receptor function by phosphorylation. 302 10

Protein kinase C isolated from retina catalyzes the stoichiometric phosphorylation of bovine rhodopsin. Enzymological studies using receptor in rod outer segment membranes stripped of peripheral proteins reveal that the phosphorylation is independent of receptor conformation or liganded state; the half-time for phosphorylation of unbleached (dark-adapted) rhodopsin, bleached (light-activated) rhodopsin, and opsin (chromophore removed) is the same. The phosphorylation by protein kinase C is Ca2+ and lipid regulated; the Km for Ca2+ decreases with increasing concentrations of membrane, consistent with known properties of Ca(2+)-regulated protein kinase Cs. The Km for ATP is 27 microM, with an optimal concentration for MgCl2 of approximately 1 mM. The phosphorylation of rhodopsin by protein kinase C is inhibited by the protein kinase C-selective inhibitor sangivamycin. Proteolysis by Asp-N reveals that all the protein kinase C phosphorylation sites are on the carboxyl terminus of the receptor. Cleavage with trypsin indicates that Ser338, the primary phosphorylation site of rhodopsin kinase, is not phosphorylated significantly; rather, the primary phosphorylation site of protein kinase C is on the membrane proximal half of the carboxyl terminus. The protein kinase C-catalyzed phosphorylation of rhodopsin is analogous to the ligand-independent phosphorylation of other G protein-coupled receptors that is catalyzed by second messenger-regulated kinases.
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PMID:Kinetics and localization of the phosphorylation of rhodopsin by protein kinase C. 789 14

Because the acute homologous phase of desensitization of the LH/CG-sensitive adenylyl cyclase in porcine follicles is readily demonstrated in a cell-free membrane preparation, it follows that any enzyme(s) required to achieve desensitization must be present in the membranes and must be activated upon LH/CG receptor activation. The purpose of the following studies was to determine whether modulation of endogenous membrane protein kinases, with activators or inhibitors, or addition of exogenous protein kinases affected desensitization of the LH/CG-sensitive adenylyl cyclase. The effects of these potential modulators were evaluated in both the presence and absence of ligand (hCG)-stimulated receptor activation. To this end, membranes were incubated in the presence or absence of hCG (stage 1) and then assayed for adenylyl cyclase activity in the presence or absence of hCG (stage 2). The results showed that although porcine follicular membranes rich in LH/CG-sensitive adenylyl cyclase activity also exhibited cAMP-dependent [protein kinase-A (PKA)], cGMP-dependent (PKG), lipid-dependent (PKC), Ca2+/calmodulin, and casein kinase-I and -II activities, only full hCG-stimulated adenylyl cyclase activity (measured with BSA in stage 1 and hCG in stage 2) was reduced upon addition of exogenous PKC (to the stage 1 incubation). hCG-dependent desensitization of cAMP synthesis (measured with hCG in stages 1 and 2) was unaffected by activators or inhibitors of endogenous PKA, PKC, or PKG, by an inhibitor of casein kinases and kinases in the beta-adrenergic receptor kinase family, or by the addition of exogenous active PKA, PKC, or rhodopsin kinase to the stage 1 incubation. These results suggest that the acute homologous phase of hCG-dependent desensitization of adenylyl cyclase activity in follicular membranes is not regulated by PKA, PKC, PKG, or messenger-independent heparin-sensitive protein kinases.
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PMID:The effect of protein kinases on desensitization of the porcine follicular membrane luteinizing hormone/chorionic gonadotropin-sensitive adenylyl cyclase. 813 39

Effects of G proteins on the phosphorylation of muscarinic receptors (mAChRs) have been examined. Cerebral but not atrial mAChRs were phosphorylated by any one of three types of protein kinase C and 4-6 mol of phosphate were incorporated per mol of mAChR, mostly in the 12-14 kDa from the carboxyterminus. Atrial mAChRs were better substrates of cAMP-dependent protein kinase than cerebral mAChRs. Phosphorylation of mAChRs by protein kinase C or cAMP-dependent protein kinase was not dependent on the presence of agonists and G proteins except that a slight inhibition by G proteins was observed probably because G proteins were also substrates of the two kinases. Agonist-dependent phosphorylation of atrial mAChRs or recombinant human mAChRs (m2 subtype) by a kinase (mAChR kinase), which is the same or very similar to beta adrenergic receptor kinase (beta ARK), was found to be regulated by the G proteins in a dual manner; stimulation by G protein beta gamma subunits and inhibition by G protein alpha beta gamma trimer. The inhibition by the G protein trimer is restored by addition of guanine nucleotides and is considered to be due to the formation of a ternary complex of agonist, mAChR and guanine nucleotide free G proteins. The stimulation by G protein beta gamma subunits was also observed for the light- or agonist-dependent phosphorylation of rhodopsin and beta AR by the mAChR kinase but not for the light-dependent phosphorylation of rhodopsin by rhodopsin kinase. The phosphorylation by beta ARK 1 was also found to be stimulated by G protein beta gamma subunits. The beta gamma subunit is considered to interact with the extra 130 amino acid residue carboxyterminal tail of beta ARK, which does not exist in rhodopsin kinase, and the interaction results in the activation of the kinase. We may assume that the G protein coupled receptor kinase is an effector of G protein beta gamma subunits and that one of the functions of beta gamma subunits is to stimulate the phosphorylation of G protein coupled receptors thereby facilitating their desensitization.
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PMID:Phosphorylation of muscarinic receptors: regulation by G proteins. 844 23

A decrease of cytoplasmic Ca(2+)-concentration in vertebrate photoreceptor cells after illumination is necessary for light adaptation. Although the mechanisms of adaptation is not completely understood, several Ca(2+)-dependent cellular processes have been discovered. Some involve calcium-binding proteins like recoverin, guanylyl cyclase-activating protein and calmodulin, and their target proteins rhodopsin kinase, guanylyl cyclase, the cGMP-gated channel, and NO synthase. The activity of several enzymes or channels is directly controlled by Ca2+ and does not involve calcium-binding proteins. These proteins are pyrophosphatase, protein kinase C and the cGMP-gated channel.
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PMID:Control of photoreceptor proteins by Ca2+. 855 70


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