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Alexandra C Newton - One of the best experts on this subject based on the ideXlab platform.
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Protein Kinase C poised to signal
American Journal of Physiology-endocrinology and Metabolism, 2010Co-Authors: Alexandra C NewtonAbstract:Nestled at the tip of a branCh of the kinome, Protein Kinase C (PKC) family members are poised to transduCe signals emanating from the Cell surfaCe. Cell membranes provide the platform for PKC funCtion, supporting the maturation of PKC through phosphorylation, its allosteriC aCtivation by binding speCifiC lipids, and, ultimately, promoting the downregulation of the enzyme. These regulatory meChanisms preCisely Control the level of signaling-Competent PKC in the Cell. Disruption of this regulation results in pathophysiologiCal states, most notably CanCer, where PKC levels are often grossly altered. This review introduCes the PKC family and then foCuses on reCent advanCes in understanding the Cellular regulation of its diaCylglyCerol-regulated members.
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dual role of pseudosubstrate in the Coordinated regulation of Protein Kinase C by phosphorylation and diaCylglyCerol
Journal of Biological Chemistry, 2000Co-Authors: Erica M Dutil, Alexandra C NewtonAbstract:The aCtivity of Protein Kinase C is reversibly regulated by an autoinhibitory pseudosubstrate, whiCh bloCks the aCtive site of the enzyme in the absenCe of aCtivators. However, before it Can be allosteriCally regulated, Protein Kinase C must first be proCessed by three ordered phosphorylations, the first of whiCh is modifiCation of the aCtivation loop Catalyzed by the phosphoinositide-dependent Kinase-1 (PDK-1). Here we use limited proteolysis to show that 1) newly synthesized Protein Kinase C adopts a Conformation in whiCh its pseudosubstrate sequenCe is removed from the aCtive site, and 2) this exposure is essential to allow PDK-1 to phosphorylate the enzyme. PreCursor (unphosphorylated) Protein Kinase C betaII obtained by 1) in vitro transCription and translation, 2) expression of a phosphorylation-defiCient mutant (T500V), or 3) in vivo labeling with a pulse of [(35)S]Cysteine/methionine is Cleaved at the amino-terminal pseudosubstrate by the endoProteinase Arg-C. In marked Contrast to mature (phosphorylated) enzyme, proteolysis oCCurs in the absenCe of lipid aCtivators, revealing that preCursor Protein Kinase C has its pseudosubstrate sequenCe removed Constitutively. Additionally, we show that PDK-1 is unable to phosphorylate Protein Kinase C when the aCtive site is steriCally bloCked by a peptide substrate. Neither Can mature enzyme be dephosphorylated when the aCtive site is bloCked by binding either the pseudosubstrate sequenCe or a heterologous substrate. Thus, the aCCessibility of the aCtivation loop to both phosphorylation and dephosphorylation requires an exposed pseudosubstrate. In summary, newly synthesized Protein Kinase C adopts a Conformation in whiCh its pseudosubstrate sequenCe is removed from the aCtive site, rendering the aCtivation loop aCCessible to phosphorylation by PDK-1. Phosphorylation serves as a Conformational switCh to position the pseudosubstrate so that it bloCks the aCtive site, a Conformation that is maintained until stimulus-dependent membrane binding releases it, thus aCtivating the enzyme.
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IdentifiCation of Protein Kinase C Phosphorylation Sites on Bovine Rhodopsin
Journal of Biological Chemistry, 1997Co-Authors: N. Michelle Greene, David S Williams, Alexandra C NewtonAbstract:AbstraCt The Protein Kinase C phosphorylation sites on bovine rhodopsin were identified using proteolytiC, phosphoamino aCid, mass speCtrometriC, and peptide sequenCing analyses. TryptiC removal of the 9 Carboxyl-terminal residues of rhodopsin revealed that a major fraCtion of the phosphates inCorporated by Protein Kinase C are in a region Containing Ser334, Thr335, and Thr336. Phosphoamino aCid analysis of the tryptiC produCt established that Ser334 aCCounts for approximately 65% of the phosphorylation in this region. Analysis of the endoProteinase Asp-N-generated Carboxyl terminus of rhodopsin by mass speCtrometry and peptide sequenCing revealed that Ser338 is also a primary phosphorylation site, with minor phosphorylation of Ser343. Quantitation of high pressure liquid Chromatography-separated phosphopeptides, taken together with phosphoamino aCid analysis of the tryptiC produCt, revealed that Ser334 and Ser338 were phosphorylated equally and eaCh aCCounted for approximately 35% of the total phosphorylation; Thr335/336 aCCounted for just under 20% of the phosphorylation, and Ser343 aCCounted for 10%. Thus, the primary Protein Kinase C sites are Ser334 and Ser338, with minor phosphorylation of Thr335/336 and Ser343. Ser334and Ser338 have reCently been identified as the primary sites of phosphorylation of rhodopsin in vivo (Ohguro, H., Van Hooser, J. P., Milam, A. H., and PalCzewski, K. (1995)J. Biol. Chem. 270, 14259–14262). Of these sites, only Ser338 is a signifiCant substrate for rhodopsin Kinasein vitro. IdentifiCation of Ser334 as a primary Protein Kinase C target in vitro is Consistent with Protein Kinase C modulating the phosphorylation of this site in vivo.
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regulation of Protein Kinase C
Current Opinion in Cell Biology, 1997Co-Authors: Alexandra C NewtonAbstract:Protein Kinase C has been in the spotlight sinCe the disCovery two deCades ago that it is aCtivated by the lipid seCond messenger diaCylglyCerol. Despite Protein Kinase C's enduring stage presenCe, the regulation and speCifiC roles of its isozymes in defined Cellular proCesses are still under intense investigation. EluCidation of the struCtures of Protein Kinase C's regulatory modules, the disCovery that phosphorylation regulates the enzyme, and the identifiCation of targeting meChanisms have made the past year a signifiCant one for unveiling how this ubiquitous Class of enzymes operates.
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Contribution of Protein Kinase C to the phosphorylation of rhodopsin in intaCt retinas
Journal of Biological Chemistry, 1997Co-Authors: Igor P Udovichenko, Alexandra C Newton, David S WilliamsAbstract:AbstraCt Similar to other G Protein-Coupled reCeptors, the visual reCeptor, rhodopsin, is phosphorylated by both a substrate-regulated Kinase, rhodopsin Kinase, and a seCond messenger-regulated Kinase, Protein Kinase C. In the present study, the extent of involvement of Protein Kinase C in the light-dependent phosphorylation of rhodopsin in intaCt retinas was assessed using a speCifiC aCtivator (phorbol ester) and speCifiC inhibitor (Calphostin C) of Protein Kinase C. KinetiC analysis of rhodopsin phosphorylation following different illumination Conditions revealed that hyperaCtivation of Protein Kinase C with phorbol ester resulted in a relative inCrease in rhodopsin phosphorylation that peaked 10-15 min after the onset of illumination. Following this period, the rate of rhodopsin dephosphorylation was inCreased in the phorbol ester-treated retinas, so that by about 30 min the amount of phosphorylation was similar to that in Control retinas. Treatment of retinas with Calphostin C, a potent regulatory domain-direCted inhibitor of Protein Kinase C, resulted in an approximately 50% reduCtion in the light-dependent phosphorylation of rhodopsin. This inhibitor had no effeCt on the aCtivity of rhodopsin Kinase in vitro Last, we show that frog rhodopsin is phosphorylated in vitro by Protein Kinase C from frog rod outer segments, indiCating that this Kinase Could direCtly modulate rhodopsin in vivo In ConClusion, the present results reveal that the kinetiCs of rhodopsin phosphorylation/dephosphorylation differ markedly, depending on whether Protein Kinase C or rhodopsin Kinase aCtivity dominates, and that, under the Conditions studied, Protein Kinase C Contributes to approximately half of the phosphorylation of rhodopsin in intaCt frog retinas.
Mark Kester - One of the best experts on this subject based on the ideXlab platform.
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interleukin 1 induCed ether linked diglyCerides inhibit CalCium insensitive Protein Kinase C isotypes impliCations for growth senesCenCe
Journal of Biological Chemistry, 1997Co-Authors: Atashi Mandal, Yizheng Wang, Paul Ernsberger, Mark KesterAbstract:It is hypothesized that inflammatory Cytokines and vasoaCtive peptides stimulate distinCt speCies of diglyCerides that differentially regulate Protein Kinase C isotypes. In published data, we demonstrated that interleukin-1, in Contrast to endothelin, seleCtively generates ether-linked diglyCeride speCies (alkyl, aCyl- and alkenyl, aCylglyCerols) in rat mesangial Cells, a smooth musCle-like periCyte in the glomerulus. We now demonstrate both in intaCt Cell and in Cell-free preparations that these interleukin-1 reCeptor-generated ether-linked diglyCerides inhibit immunopreCipitated Protein Kinase C delta and epsilon but not zeta aCtivity. Neither interleukin-1 nor endothelin affeCt de novo Protein expression of these Protein Kinase C isotypes. As down-regulation of CalCium-insensitive Protein Kinase C isotypes has been linked to antimitogeniC aCtivity, we investigated growth arrest as a funCtional Correlate for IL-1-generated ether-linked diglyCerides. Cell-permeable ether-linked diglyCerides mimiC the effeCts of interleukin-1 to induCe a growth-arrested state in both G-Protein-linked reCeptor- and tyrosine Kinase reCeptor-stimulated mesangial Cells. This signaling meChanism impliCates Cytokine reCeptor-induCed ether-linked diglyCerides as seCond messengers that inhibit the bioaCtivity of CalCium-insensitive Protein Kinase C isotypes resulting in growth arrest.
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interleukin 1 and endothelin stimulate distinCt speCies of diglyCerides that differentially regulate Protein Kinase C in mesangial Cells
Journal of Biological Chemistry, 1995Co-Authors: Angela Musial, Atashi Mandal, E Coroneos, Mark KesterAbstract:AbstraCt DiglyCerides are phospholipid-derived seCond messengers that serve as CofaCtors for Protein Kinase C aCtivation. We have previously shown that, in rat glomerular mesangial Cells, the Cytokine, interleukin-1α, and the vasoaCtive peptide, endothelin, generate diglyCerides from unique phospholipid preCursors. However, neither the moleCular speCies of these diglyCerides nor their biologiCal aCtions were determined. It is now hypothesized that interleukin-1- and endothelin-treated mesangial Cells form distinCt moleCular speCies of diglyCerides whiCh may serve different roles as intraCellular signaling moleCules. DiglyCeride moleCular speCies were resolved and quantified by TLC and high performanCe liquid Chromatography as diglyCeride-[C]aCetate derivatives. Endothelin stimulates predominantly ester-linked speCies (diaCylglyCerols) in Contrast to interleukin-1 whiCh stimulates only ether-linked speCies (alkyl,aCyl- and alkenyl,aCylglyCerols). In support of these data, interleukin-1-treated mesangial Cells hydrolyze ethanolamine plasmalogens, vinyl ether-linked phospholipids. It has been reported that ether-linked, in Contrast to ester-linked, diglyCeride speCies do not aCtivate Protein Kinase C aCtivity. Thus, we next assessed membrane Protein Kinase C aCtivity in endothelin- or interleukin-1-treated mesangial Cells. Even though interleukin-1 has no effeCt upon basal Protein Kinase C aCtivity, this Cytokine, through the formation of ether-linked diglyCeride seCond messengers, inhibits endothelin, platelet-aCtivating faCtor, or arginine vasopressin-stimulated Protein Kinase C aCtivity. We further demonstrate that ester-linked diaCylglyCerols but not alkyl,aCyl- or alkenyl,aCylglyCerols substitute for phorbol esters in a Cell-free Protein Kinase C assay. In addition, alkenyl,aCylglyCerols inhibit diaCylglyCerol-stimulated immunopreCipitated Protein Kinase C α aCtivity in vitro and total Protein Kinase C aCtivity in permeabilized mesangial Cells ex vivo. Taken together, these data suggest that interleukin-1-induCed formation of ether-linked diglyCerides may physiologiCally serve to down-regulate reCeptor-mediated Protein Kinase C aCtivity and that individual moleCular speCies of diglyCerides may serve different roles as intraCellular signaling moleCules.
James M Downey - One of the best experts on this subject based on the ideXlab platform.
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preConditioning proteCts isChemiC rabbit heart by Protein Kinase C aCtivation
American Journal of Physiology-heart and Circulatory Physiology, 1994Co-Authors: Kirsti Ytrehus, James M DowneyAbstract:MyoCardial proteCtion in the rabbit induCed by isChemiC preConditioning is thought to be adenosine reCeptor linked, but the signaling pathway responsible for the proteCtion has yet to be identified. This study tests whether Protein Kinase C Could be involved. Either of two inhibitors of Protein Kinase C, staurosporine (50 miCrograms/kg) or polymyxin B (24 mg/kg), were administered to rabbits subjeCted to 30 min regional myoCardial isChemia followed by 180 min reperfusion. Half of the rabbits were preConditioned while the other half served as nonpreConditioned Controls. NonpreConditioned hearts without drug or treated with staurosporine or polymyxin B resulted in 37.8 +/- 3.1, 40.5 +/- 2.8, and 42.0 +/- 7.0% infarCtion of the risk zone, respeCtively. PreConditioning limited infarCt size to 7.3 +/- 2.7%. Both inhibitors bloCked proteCtion in preConditioned hearts with 36.2 +/- 2.7 and 40.9 +/- 2.5% of the risk zone infarCted, respeCtively. ACtivation of Protein Kinase C with 4 beta-phorbol 12-myristate 13-a...
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preConditioning proteCts isChemiC rabbit heart by Protein Kinase C aCtivation
American Journal of Physiology-heart and Circulatory Physiology, 1994Co-Authors: Kirsti Ytrehus, Yongge Liu, James M DowneyAbstract:MyoCardial proteCtion in the rabbit induCed by isChemiC preConditioning is thought to be adenosine reCeptor linked, but the signaling pathway responsible for the proteCtion has yet to be identified. This study tests whether Protein Kinase C Could be involved. Either of two inhibitors of Protein Kinase C, staurosporine (50 miCrograms/kg) or polymyxin B (24 mg/kg), were administered to rabbits subjeCted to 30 min regional myoCardial isChemia followed by 180 min reperfusion. Half of the rabbits were preConditioned while the other half served as nonpreConditioned Controls. NonpreConditioned hearts without drug or treated with staurosporine or polymyxin B resulted in 37.8 +/- 3.1, 40.5 +/- 2.8, and 42.0 +/- 7.0% infarCtion of the risk zone, respeCtively. PreConditioning limited infarCt size to 7.3 +/- 2.7%. Both inhibitors bloCked proteCtion in preConditioned hearts with 36.2 +/- 2.7 and 40.9 +/- 2.5% of the risk zone infarCted, respeCtively. ACtivation of Protein Kinase C with 4 beta-phorbol 12-myristate 13-aCetate (PMA) or with 1-oleyl-2-aCetyl glyCerol (OAG) mimiCked preConditioning in buffer-perfused hearts. PMA (0.01 nmol/min) or OAG (10 nmol/min) for 5 min was followed by 10 min of washout. InfarCt size after 30 min regional isChemia was limited in the PMA and OAG groups (6.4 +/- 1.4 and 11.7 +/- 3.3 vs. 28.0 +/- 4.5% in untreated Controls) and was equipotent with isChemiC preConditioning (11.8 +/- 2.2%). Polymyxin B also bloCked proteCtion from isChemiC preConditioning in the isolated heart (33.0 +/- 5.0%).(ABSTRACT TRUNCATED AT 250 WORDS)
George M. Carman - One of the best experts on this subject based on the ideXlab platform.
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phosphorylation of the yeast phospholipid synthesis regulatory Protein opi1p by Protein Kinase C
Journal of Biological Chemistry, 2001Co-Authors: Avula Sreenivas, Manuel J Villagarcia, Susan A Henry, George M. CarmanAbstract:Opi1p is a negative regulator of expression of phospholipid-synthesizing enzymes in the yeast SaCCharomyCes Cerevisiae. In this work, we examined the phosphorylation of Opi1p by Protein Kinase C. Using a purified maltose-binding Protein-Opi1p fusion Protein as a substrate, Protein Kinase C aCtivity was time- and dose-dependent, and dependent on the ConCentrations of Opi1p and ATP. Protein Kinase C phosphorylated Opi1p on a serine residue. The Opi1p synthetiC peptide GVLKQSCRQK, whiCh Contained a Protein Kinase C sequenCe motif at Ser 26 , was a substrate for Protein Kinase C. Phosphorylation of a purified S26A mutant maltose-binding Protein-Opi1p fusion Protein by the Kinase was reduCed when Compared with the wild-type Protein. A major phosphopeptide present in purified wild-type Opi1p was absent from the purified S26A mutant Protein. In vivo labeling experiments showed that the phosphorylation of Opi1p was physiologiCally relevant, and that the extent of phosphorylation of the S26A mutant Protein was reduCed by 50% when Compared with the wild-type Protein. The physiologiCal ConsequenCe of the phosphorylation of Opi1p at Ser 26 was examined by measuring the effeCt of the S26A mutation on the expression of the phospholipid synthesis gene INO1. The -galaCtosidase aCtivity driven by an INO1CYC-laCIZ reporter gene in opi1 mutant Cells expressing the S26A mutant Opi1p was about 50% lower than that of Cells expressing the wild-type Opi1p Protein. These data supported the ConClusion that phosphorylation of Opi1p at Ser 26 mediated the attenuation of the negative regulatory funCtion of Opi1p on the expression of the INO1 gene.
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phosphorylation of Ctp synthetase from saCCharomyCes Cerevisiae by Protein Kinase C
Journal of Biological Chemistry, 1995Co-Authors: Wenglang Yang, George M. CarmanAbstract:AbstraCt Phosphorylation of CTP synthetase (EC 6.3.4.2, UTP:ammonia ligase (ADP-forming)) from SaCCharomyCes Cerevisiae by Protein Kinase C was examined. Using pure CTP synthetase as a substrate, Protein Kinase C aCtivity was dose- and time-dependent and required CalCium, diaCylglyCerol, and phosphatidylserine for full aCtivation. Protein Kinase C aCtivity was also dependent on the ConCentration of CTP synthetase. Protein Kinase C phosphorylated CTP synthetase on serine and threonine residues in vitro whereas the enzyme was primarily phosphorylated on serine residues in vivo. Phosphopeptide mapping analysis of CTP synthetase phosphorylated in vitro and in vivo indiCated that the enzyme was phosphorylated on more than one site. Most of the phosphopeptides derived from CTP synthetase phosphorylated in vivo were the same as those derived from CTP synthetase phosphorylated by Protein Kinase C in vitro. The stoiChiometry of the phosphorylation of native CTP synthetase was 0.4 mol of phosphate/mol of enzyme whereas the stoiChiometry of the phosphorylation of alkaline phosphatase-treated CTP synthetase was 2.2 mol of phosphate/mol of enzyme. This indiCated that CTP synthetase was purified in a phosphorylated state. Phosphorylation of CTP synthetase resulted in a 3-fold aCtivation in enzyme aCtivity whereas alkaline phosphatase treatment of CTP synthetase resulted in a 5-fold deCrease in enzyme aCtivity. Overall, the results reported here were Consistent with the ConClusion that CTP synthetase was regulated by Protein Kinase C phosphorylation.
David S Williams - One of the best experts on this subject based on the ideXlab platform.
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IdentifiCation of Protein Kinase C Phosphorylation Sites on Bovine Rhodopsin
Journal of Biological Chemistry, 1997Co-Authors: N. Michelle Greene, David S Williams, Alexandra C NewtonAbstract:AbstraCt The Protein Kinase C phosphorylation sites on bovine rhodopsin were identified using proteolytiC, phosphoamino aCid, mass speCtrometriC, and peptide sequenCing analyses. TryptiC removal of the 9 Carboxyl-terminal residues of rhodopsin revealed that a major fraCtion of the phosphates inCorporated by Protein Kinase C are in a region Containing Ser334, Thr335, and Thr336. Phosphoamino aCid analysis of the tryptiC produCt established that Ser334 aCCounts for approximately 65% of the phosphorylation in this region. Analysis of the endoProteinase Asp-N-generated Carboxyl terminus of rhodopsin by mass speCtrometry and peptide sequenCing revealed that Ser338 is also a primary phosphorylation site, with minor phosphorylation of Ser343. Quantitation of high pressure liquid Chromatography-separated phosphopeptides, taken together with phosphoamino aCid analysis of the tryptiC produCt, revealed that Ser334 and Ser338 were phosphorylated equally and eaCh aCCounted for approximately 35% of the total phosphorylation; Thr335/336 aCCounted for just under 20% of the phosphorylation, and Ser343 aCCounted for 10%. Thus, the primary Protein Kinase C sites are Ser334 and Ser338, with minor phosphorylation of Thr335/336 and Ser343. Ser334and Ser338 have reCently been identified as the primary sites of phosphorylation of rhodopsin in vivo (Ohguro, H., Van Hooser, J. P., Milam, A. H., and PalCzewski, K. (1995)J. Biol. Chem. 270, 14259–14262). Of these sites, only Ser338 is a signifiCant substrate for rhodopsin Kinasein vitro. IdentifiCation of Ser334 as a primary Protein Kinase C target in vitro is Consistent with Protein Kinase C modulating the phosphorylation of this site in vivo.
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Contribution of Protein Kinase C to the phosphorylation of rhodopsin in intaCt retinas
Journal of Biological Chemistry, 1997Co-Authors: Igor P Udovichenko, Alexandra C Newton, David S WilliamsAbstract:AbstraCt Similar to other G Protein-Coupled reCeptors, the visual reCeptor, rhodopsin, is phosphorylated by both a substrate-regulated Kinase, rhodopsin Kinase, and a seCond messenger-regulated Kinase, Protein Kinase C. In the present study, the extent of involvement of Protein Kinase C in the light-dependent phosphorylation of rhodopsin in intaCt retinas was assessed using a speCifiC aCtivator (phorbol ester) and speCifiC inhibitor (Calphostin C) of Protein Kinase C. KinetiC analysis of rhodopsin phosphorylation following different illumination Conditions revealed that hyperaCtivation of Protein Kinase C with phorbol ester resulted in a relative inCrease in rhodopsin phosphorylation that peaked 10-15 min after the onset of illumination. Following this period, the rate of rhodopsin dephosphorylation was inCreased in the phorbol ester-treated retinas, so that by about 30 min the amount of phosphorylation was similar to that in Control retinas. Treatment of retinas with Calphostin C, a potent regulatory domain-direCted inhibitor of Protein Kinase C, resulted in an approximately 50% reduCtion in the light-dependent phosphorylation of rhodopsin. This inhibitor had no effeCt on the aCtivity of rhodopsin Kinase in vitro Last, we show that frog rhodopsin is phosphorylated in vitro by Protein Kinase C from frog rod outer segments, indiCating that this Kinase Could direCtly modulate rhodopsin in vivo In ConClusion, the present results reveal that the kinetiCs of rhodopsin phosphorylation/dephosphorylation differ markedly, depending on whether Protein Kinase C or rhodopsin Kinase aCtivity dominates, and that, under the Conditions studied, Protein Kinase C Contributes to approximately half of the phosphorylation of rhodopsin in intaCt frog retinas.
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KinetiCs and LoCalization of the Phosphorylation of Rhodopsin by Protein Kinase C
Journal of Biological Chemistry, 1995Co-Authors: N. Michelle Greene, David S Williams, Alexandra C NewtonAbstract:AbstraCt 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 Ca and lipid regulated; the K for Ca deCreases with inCreasing ConCentrations of membrane, Consistent with known properties of Ca-regulated Protein Kinase Cs. The K for ATP is 27 μM, 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 Ser, 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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involvement of Protein Kinase C in the phosphorylation of rhodopsin
Journal of Biological Chemistry, 1991Co-Authors: Alexandra C Newton, David S WilliamsAbstract:AbstraCt 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.
