101
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Omer CA, Kral AM, Diehl RE, Prendergast GC, Powers S, Allen CM, Gibbs JB, Kohl NE. Characterization of recombinant human farnesyl-protein transferase: cloning, expression, farnesyl diphosphate binding, and functional homology with yeast prenyl-protein transferases. Biochemistry 1993; 32:5167-76. [PMID: 8494894 DOI: 10.1021/bi00070a028] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We have isolated cDNAs encoding the alpha and beta subunits of human farnesyl-protein transferase (FPTase). The proteins encoded by these two cDNAs are 93-95% identical to the corresponding subunits of bovine and rat FPTase and show regions of homology with proteins encoded by Saccharomyces cerevisiae prenyl-protein transferase genes. Human FPTase expressed in Escherichia coli from a translationally coupled operon had kinetic properties similar to those of FPTase isolated from bovine brain. Examination of farnesyl diphosphate binding indicated that while neither individual subunit was capable of isoprenoid binding, a radiolabeled farnesyl diphosphate analog could be specifically photo-cross-linked to the beta subunit of FPTase holoenzyme. To further analyze subunit structure-function and to detect functional similarities with yeast prenyl-protein transferases (FPTase and two geranylgeranyl-protein transferases), amino acid changes homologous to those found in mutant yeast prenyl-protein transferase subunits were made in the subunits of human FPTase. Substitutions in either the alpha or beta subunits that decrease the activity of yeast prenyl-protein transferases were also observed to impair human FPTase. Kinetic analyses showed that these mutant human FPTases have Km and kcat values that are altered with respect to wild-type human FPTase.
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Affiliation(s)
- C A Omer
- Department of Cancer Research, Merck Research Laboratories, West Point, Pennsylvania 19486
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102
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Abstract
The isoprenylation pathway requires an endoprotease that cleaves the modified protein at the isoprenylated cysteine residue. This endoprotease was readily assayed with simple tetrapeptide substrates of the type N-acetyl-S-farnesyl-L-Cys-(AFC)-Val-Ile-Met, where AFC and the tripeptide are the products of the hydrolysis. The endoprotease proved to be unaffected by (1) serine protease inhibitors, including (4-amidinophenyl)methanesulfonyl fluoride, aprotinin, and leupeptin, by (2) cysteine protease inhibitors, including E-64 and leupeptin [the enzyme is, however, inhibited by p-(hydroxymercuri)benzoate], by (3) metalloprotease inhibitors, including phosphoramidon, EDTA, and 1,10-phenanthroline, or by (4) the aspartyl protease inhibitor pepstatin. The conclusion from these data is that the enzyme is probably not a metalloenzyme. N-Boc-S-all-trans-farnesyl-L-cysteine (BFC) derivatives containing a statine moiety are also not inhibitory, strongly suggesting that the enzyme is not an aspartyl protease. However, the enzyme is potently inhibited by the aldehyde derivative of BFC (K1 = 1.9 microM), which is consistent with the idea that the enzyme is a serine or cysteine protease. Potent tetrapeptide-based competitive inhibitors were prepared. Analogs with the scissile bond modified so that hydrolysis could not occur were excellent inhibitors. An analog containing BFC-statine-Val-Ile-Met inhibited the endoprotease with a K1 = 64 nM. The equivalent pseudopeptide psi (CH2-NH) analog was almost as potent, indicating that the statine moiety simply represents a nonhydrolyzable linker.
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Affiliation(s)
- Y T Ma
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115
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103
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Wildman DE, Tamir H, Leberer E, Northup JK, Dennis M. Prenyl modification of guanine nucleotide regulatory protein gamma 2 subunits is not required for interaction with the transducin alpha subunit or rhodopsin. Proc Natl Acad Sci U S A 1993; 90:794-8. [PMID: 8430087 PMCID: PMC45756 DOI: 10.1073/pnas.90.3.794] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Guanine nucleotide-binding regulatory protein (G protein) beta gamma dimers that were active in reconstitution assays were produced in insect cells using the baculovirus/Sf9 insect cell expression system. Sf9 cells were infected either singly or in combination with recombinant baculoviruses containing a human G-protein beta 1 gene or a bovine G-protein gamma 2 gene. It was possible to express the beta 1 and gamma 2 gene products independently of each other in this system, as determined by using immunological and metabolic labeling techniques. Further, the ability of recombinant beta and/or gamma chains to function in defined biochemical assays of beta gamma activity was assessed for membrane extracts and supernatant fractions from infected Sf9 cells. Extracts of cells expressing beta or gamma chain alone were inactive in these assays, whereas those from cells coinfected with beta 1 and gamma 2 did display activity. These assays were used to identify recombinant beta gamma dimer migration during chromatographic purification, and the recombinant dimers were purified to near homogeneity. Both the membrane-associated and soluble beta gamma dimers facilitated rhodopsin-catalyzed guanosine 5'-[gamma-thio]triphosphate binding to Gt alpha, the GTP-binding subunit of the retinal G protein transducin (K0.5 of 13 +/- 2 and 36 +/- 5 nM, respectively). Both recombinant beta gamma dimers also facilitated the pertussis toxin-catalyzed ADP-ribosylation of Gt alpha with equal potency (K0.5 of 9 +/- 1 and 10 +/- 3 nM for membrane and soluble dimers, respectively). [3H]Mevalonolactone labeling showed that the gamma 2 subunits of membrane-associated beta gamma dimers incorporated radiolabel, whereas in the soluble form they did not. Thus, prenyl modification of gamma 2 directs the membrane association of the beta 1 gamma 2 dimer and increases its apparent affinity for receptor, but it is not required for the functional interaction(s) of the dimer.
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Affiliation(s)
- D E Wildman
- Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510
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104
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Isolation and Characterization of Rod Outer Segment Disk and Plasma Membranes. ACTA ACUST UNITED AC 1993. [DOI: 10.1016/b978-0-12-185279-5.50014-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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105
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Kawamura S. Molecular aspects of photoreceptor adaptation in vertebrate retina. INTERNATIONAL REVIEW OF NEUROBIOLOGY 1993; 35:43-86. [PMID: 8463064 DOI: 10.1016/s0074-7742(08)60568-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- S Kawamura
- Department of Physiology, Keio University School of Medicine, Tokyo, Japan
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106
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Affiliation(s)
- P A Hargrave
- Department of Ophthalmology, School of Medicine, University of Florida, Gainesville 32610
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107
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Morishita R, Fukada Y, Kokame K, Yoshizawa T, Masuda K, Niwa M, Kato K, Asano T. Identification and isolation of common and tissue-specific geranylgeranylated gamma subunits of guanine-nucleotide-binding regulatory proteins in various tissues. EUROPEAN JOURNAL OF BIOCHEMISTRY 1992; 210:1061-9. [PMID: 1483450 DOI: 10.1111/j.1432-1033.1992.tb17512.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Heterotrimeric guanine-nucleotide-binding regulatory proteins (G proteins) have been classified into several subtypes on the basis of the properties of their alpha subunits, though a notable multiplicity of gamma subunits has also been demonstrated. To investigate whether each subtype of alpha subunit is associated with a particular gamma subunit, various oligomeric G proteins, purified from bovine tissues, were subjected to gel electrophoresis in a Tricine buffer system. All G proteins examined were shown to have more than two kinds of gamma subunit. Of the brain G proteins, GoA, GoB, and Gi1 contain the same set of three gamma subunits, but Gi2 contains only two of these subunits. Lung Gi1 and Gi2 and spleen Gi2 and Gi3 had similar sets of two gamma subunits, one of which was distinct from the gamma subunits of brain G proteins. These observations indicate that each subtype of alpha subunit is associated with a variety of beta gamma subunits, and that the combinations differ among cells. For analyses of the structural diversity of the gamma subunits, beta gamma subunits were purified from the total G proteins of each tissue and subjected to reverse-phase HPLC under denaturing conditions, where none of the beta subunits were eluted from the column. Three distinct gamma subunits were isolated in this way from brain beta gamma subunits. In contrast, lung and spleen beta gamma subunits contained at least five gamma subunits, the elution positions and electrophoretic mobilities of which were indistinguishable between the two tissues. Among several gamma subunits, two subspecies appeared to be common to the three tissues. In fact, in each case, the partial amino acid sequence of the most abundant gamma subunit in each tissue was identical, and the sequences coincided exactly with that of 'gamma 6' [Robishaw, J. D., Kalman, V. K., Moomaw, C. R. & Slaughter, C. A. (1989) J. Biol. Chem. 264, 15758-15761]. Fast-atom-bombardment mass spectrometry analysis indicated that this abundant gamma subunit in lung and spleen was geranylgeranylated and carboxymethylated at the C-terminus, as was 'gamma 6' from brain. In addition to abundant gamma subunits, other tissue-specific gamma subunits were also shown to be geranylgeranylated by gas-chromatography-coupled mass spectrometry analysis of Raney nickel-treated gamma subunits. These results suggest that most gamma subunits associated with many different subtypes of alpha subunit are geranylgeranylated in a variety of tissues, with the single exception being the retina where the G protein transducin has a farnesylated gamma subunit.
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Affiliation(s)
- R Morishita
- Department of Biochemistry, Institute for Developmental Research, Aichi Prefectural Colony, Japan
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108
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109
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110
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Juhnn YS, Jones TL, Spiegel AM. Amino- and carboxy-terminal deletion mutants of Gs alpha are localized to the particulate fraction of transfected COS cells. J Cell Biol 1992; 119:523-30. [PMID: 1400589 PMCID: PMC2289663 DOI: 10.1083/jcb.119.3.523] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
To elucidate the structural basis for membrane attachment of the alpha subunit of the stimulatory G protein (Gs alpha), mutant Gs alpha cDNAs with deletions of amino acid residues in the amino and/or carboxy termini were transiently expressed in COS-7 cells. The particulate and soluble fractions prepared from these cells were analyzed by immunoblot using peptide specific antibodies to monitor distribution of the expressed proteins. Transfection of mutant forms of Gs alpha with either 26 amino terminal residues deleted (delta 3-28) or with 59 amino terminal residues deleted (delta 1-59) resulted in immunoreactive proteins which localized primarily to the particulate fraction. Similarly, mutants with 10 (delta 385-394), 32 (delta 353-384), or 42 (delta 353-394) amino acid residues deleted from the carboxy terminus also localized to the particulate fraction, as did a mutant form of Gs alpha lacking amino acid residues at both the amino and carboxy termini (delta 3-28)/(delta 353-384). Mutant and wild type forms of Gs alpha demonstrated a similar degree of tightness in their binding to membranes as demonstrated by treatment with 2.5 M NaCl or 6 M urea, but some mutant forms were relatively resistant compared with wild type Gs alpha to solubilization by 15 mM NaOH or 1% sodium cholate. We conclude that: (a) deletion of significant portions of the amino and/or carboxyl terminus of Gs alpha is still compatible with protein expression; (b) deletion of these regions is insufficient to cause cytosolic localization of the expressed protein. The basis of Gs alpha membrane targeting remains to be elucidated.
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Affiliation(s)
- Y S Juhnn
- Molecular Pathophysiology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
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111
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A simple synthetic process for the elaboration of oligoprenols by stereospecific coupling of di-, tri-, or oligoisoprenoid units. Tetrahedron Lett 1992. [DOI: 10.1016/s0040-4039(00)79008-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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112
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Adamson P, Marshall C, Hall A, Tilbrook P. Post-translational modifications of p21rho proteins. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)88661-1] [Citation(s) in RCA: 295] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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113
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Ehret-Hilberer S, Nullans G, Aunis D, Virmaux N. Mono ADP-ribosylation of transducin catalyzed by rod outer segment extract. FEBS Lett 1992; 309:394-8. [PMID: 1516716 DOI: 10.1016/0014-5793(92)80814-w] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Transducin is the retinal rod outer segment (ROS)-specific G protein coupling the photoexcited rhodopsin to cyclic GMP-phosphodiesterase. The alpha subunit of transducin is known to be ADP-ribosylated by bacterial toxins. We investigated the possibility that transducin is modified in vitro by an endogenous ADP-ribosyltransferase activity. By using either ROS, cytosolic extract of ROS or purified transducin in the presence of [alpha-32P]nicotinamide adenine dinucleotide (NAD+), the alpha and beta subunits of transducin were found to be radiolabeled. The labeling was decreased by snake venom phosphodiesterase I (PDE I). The modification was shown to be mono ADP-ribosylation by analyses on thin layer chromatography of the PDE I-hydrolyzed products which revealed only 5'AMP residues. In addition we report that sodium nitroprusside activates the ADP-ribosylation of transducin.
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114
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Pitcher JA, Inglese J, Higgins JB, Arriza JL, Casey PJ, Kim C, Benovic JL, Kwatra MM, Caron MG, Lefkowitz RJ. Role of beta gamma subunits of G proteins in targeting the beta-adrenergic receptor kinase to membrane-bound receptors. Science 1992; 257:1264-7. [PMID: 1325672 DOI: 10.1126/science.1325672] [Citation(s) in RCA: 555] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The rate and extent of the agonist-dependent phosphorylation of beta 2-adrenergic receptors and rhodopsin by beta-adrenergic receptor kinase (beta ARK) are markedly enhanced on addition of G protein beta gamma subunits. With a model peptide substrate it was demonstrated that direct activation of the kinase could not account for this effect. G protein beta gamma subunits were shown to interact directly with the COOH-terminal region of beta ARK, and formation of this beta ARK-beta gamma complex resulted in receptor-facilitated membrane localization of the enzyme. The beta gamma subunits of transducin were less effective at both enhancing the rate of receptor phosphorylation and binding to the COOH-terminus of beta ARK, suggesting that the enzyme preferentially binds specific beta gamma complexes. The beta gamma-mediated membrane localization of beta ARK serves to intimately link receptor activation to beta ARK-mediated desensitization.
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Affiliation(s)
- J A Pitcher
- Howard Hughes Medical Research Institute, Department of Medicine, Duke University Medical Center, Durham, NC 27710
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115
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Ma YT, Rando RR. A microsomal endoprotease that specifically cleaves isoprenylated peptides. Proc Natl Acad Sci U S A 1992; 89:6275-9. [PMID: 1631119 PMCID: PMC49483 DOI: 10.1073/pnas.89.14.6275] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
A microsomal enzymatic activity is described that can specifically cleave the tetrapeptide N-acetyl-S-farnesyl-L-Cys-L-Val-L-Ile-L-Ser between the isoprenylated cysteine residue and the valine residue. Km and Vmax values are measured as 5.8 microM and 251 pmol/min per mg of protein, respectively. Proteolytic cleavage of the substrate is stereospecific because the substitution of a farnesylated D-cysteine residue for the L-amino acid leads to the abolition of substrate activity. A free carboxyl-terminal group is also required for substrate activity because methyl esterification renders the substrate inert. The tripeptide N-acetyl-S-farnesyl-L-Cys-L-Val-L-Ile and the dipeptide N-acetyl-S-farnesyl-L-Cys-L-Val are also hydrolyzed by the protease. Again, stereospecificity is observed at the isoprenylated residue. Hydrolysis of the farnesylated tetrapeptide is not inhibited by a 5-fold excess of the nonfarnesylated tetrapeptide, suggesting that isoprenylation is important for substrate activity. This activity is probably the same as the proteolytic activity proposed to cleave isoprenylated proteins terminating in a Cys-Ali-Ali-Xaa motif, where Ali refers to aliphatic amino acid. These proteins include the ras family of G proteins and the heterotrimeric G proteins. Proteolytic maturation of these essential isoprenylated signal-transducing elements is a key step in their activation.
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Affiliation(s)
- Y T Ma
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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116
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Pronin AN, Gautam N. Interaction between G-protein beta and gamma subunit types is selective. Proc Natl Acad Sci U S A 1992; 89:6220-4. [PMID: 1631113 PMCID: PMC49470 DOI: 10.1073/pnas.89.13.6220] [Citation(s) in RCA: 134] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Signal-transducing guanine nucleotide-binding proteins (G proteins) are made up of three subunits, alpha, beta, and gamma. Each of these subunits comprises a family of proteins. The rules for association between members of one family with members of another to form a multimer are not known; it is not clear whether associations are specific or nonspecific. Other than transducin (Gt), the G protein in rod photoreceptors, most purified G proteins contain more than one subtype of beta or gamma subunits. The Gt alpha subunit is associated only with beta 1 and gamma 1. It is not known whether this specificity is due to the differential expression of these subunit types in a cell type or due to intrinsically different affinities between different beta and gamma subunit types. We have used a transfected cell assay system to examine the association of the beta 1, beta 2, and beta 3 proteins with the gamma 1 and gamma 2 proteins. Results show that gamma 1 does not associate with beta 2 and that beta 3 does not associate with gamma 1 or gamma 2. Differences in affinities between types of G protein subunits will impose restrictions on the formation of certain heterotrimers and determine which G protein will be active in a cell. A chimeric molecule of beta 1 and beta 2 was used to broadly map the regions on these subunits that determine specificity of association.
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Affiliation(s)
- A N Pronin
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110
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117
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Specific isoprenoid modification is required for function of normal, but not oncogenic, Ras protein. Mol Cell Biol 1992. [PMID: 1375323 DOI: 10.1128/mcb.12.6.2606] [Citation(s) in RCA: 117] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
While the Ras C-terminal CAAX sequence signals modification by a 15-carbon farnesyl isoprenoid, the majority of isoprenylated proteins in mammalian cells are modified instead by a 20-carbon geranylgeranyl moiety. To determine the structural and functional basis for modification of proteins by a specific isoprenoid group, we have generated chimeric Ras proteins containing C-terminal CAAX sequences (CVLL and CAIL) from geranylgeranyl-modified proteins and a chimeric Krev-1 protein containing the H-Ras C-terminal CAAX sequence (CVLS). Our results demonstrate that both oncogenic Ras transforming activity and Krev-1 antagonism of Ras transforming activity can be promoted by either farnesyl or geranylgeranyl modification. Similarly, geranylgeranyl-modified normal Ras [Ras(WT)CVLL], when overexpressed, exhibited the same level of transforming activity as the authentic farnesyl-modified normal Ras protein. Therefore, farnesyl and geranylgeranyl moieties are functionally interchangeable for these biological activities. In contrast, expression of moderate levels of geranylgeranyl-modified normal Ras inhibited the growth of untransformed NIH 3T3 cells. This growth inhibition was overcome by coexpression of the mutant protein with oncogenic Ras or Raf, but not with oncogenic Src or normal Ras. The similar growth-inhibiting activities of Ras(WT)CVLL and the previously described Ras(17N) dominant inhibitory mutant suggest that geranylgeranyl-modified normal Ras may exert its growth-inhibiting action by perturbing endogenous Ras function. These results suggest that normal Ras function may specifically require protein modification by a farnesyl, but not a geranylgeranyl, isoprenoid.
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118
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Tan EW, Rando RR. Identification of an isoprenylated cysteine methyl ester hydrolase activity in bovine rod outer segment membranes. Biochemistry 1992; 31:5572-8. [PMID: 1610803 DOI: 10.1021/bi00139a021] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Proteins from eucaryotic cells which have a carboxyl-terminal CAAX motif are posttranslationally modified by isoprenylation. The pathway involves the linkage of an all-trans-farnesyl (C15) or an all-trans-geranylgeranyl (C20) moiety to the cysteine residue followed by proteolysis which generates the modified cysteine as the carboxyl-terminal residue. Carboxylmethylation of the modified cysteine residue completes the pathway. This latter methylation reaction is the only potentially reversible reaction in the pathway and thus of possible regulatory significance. A specific esterase is required to reverse the methylation. It is demonstrated here that simple isoprenylated cysteine derivatives, such as N-acetyl-S-farnesyl-L-cysteine methyl ester (L-AFCM) and N-acetyl-S-geranylgeranyl-L-cysteine methyl ester (L-AGGCM), are substrates for a rod outer segment (ROS) membrane esterase activity. The KM and Vmax values for L-AFCM and L-AGGCM are 186 microM and 2.2 nmol mg-1 min-1 and 435 microM and 4.8 nmol mg-1 min-1, respectively. The enzyme(s) is stereoselective rather than stereospecific because D-AFCM is enzymatically hydrolyzed with KM and Vmax values of 157 microM and 0.46 nmol mg-1 min-1, respectively. The enzyme(s) does not process N-acetyl-L-cysteine methyl ester, demonstrating that the isoprenyl moiety is required for substrate activity. Ebelactone B is a potent mechanism-based inactivator of the enzyme with a KI = 42 microM and a kinh = 3.7 x 10(-3) s-1. Importantly, L-AFCM, L-AGGCM, and ebelactone B all inhibit the demethylation of the endogenous ROS substrates, showing that the same enzymatic activity is involved in the processing of the synthetic and physiological substrates.
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Affiliation(s)
- E W Tan
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115
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119
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Pérez-Sala D, Gilbert BA, Tan EW, Rando RR. Prenylated protein methyltransferases do not distinguish between farnesylated and geranylgeranylated substrates. Biochem J 1992; 284 ( Pt 3):835-40. [PMID: 1622400 PMCID: PMC1132615 DOI: 10.1042/bj2840835] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Proteins that are post-translationally modified by prenylation can be either farnesylated (C-15) or geranylgeranylated (C-20) by separate prenyltransferase enzymes. Prenylated proteins are also methylated at their C-terminal residue by S-adenosylmethionine-linked methylation. In this paper we show that the methylation of farnesylated and geranyl-geranylated substrates can be accounted for by the presence of a single enzyme. It is demonstrated that the Km and Vmax. values for the retinal rod outer segment methyltransferase, measured with small molecule farnesylated and geranylgeranylated substrates, are identical. These substrates mutually inhibit each other's methylation, with KI values being equal to their Km values. The Km for S-adenosylmethionine was measured to be the same with either farnesylated or geranylgeranylated substrates. Competitive inhibitors of the methyltransferase containing either a geranylgeranyl or a farnesyl group equally block the methylation of synthetic geranylgeranylated and farnesylated substrates of the enzyme. Importantly, these inhibitors are also equipotent at inhibiting the methylation of the physiological substrates of the rod outer segment methyltransferase. These substrates are both farnesylated and geranylgeranylated. One of these substrates had previously been identified as the farnesylated gamma subunit of transducin. Therefore it appears that the same enzymic activity can methylate both farnesylated and geranylgeranylated substrates.
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Affiliation(s)
- D Pérez-Sala
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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120
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Cox AD, Hisaka MM, Buss JE, Der CJ. Specific isoprenoid modification is required for function of normal, but not oncogenic, Ras protein. Mol Cell Biol 1992; 12:2606-15. [PMID: 1375323 PMCID: PMC364454 DOI: 10.1128/mcb.12.6.2606-2615.1992] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
While the Ras C-terminal CAAX sequence signals modification by a 15-carbon farnesyl isoprenoid, the majority of isoprenylated proteins in mammalian cells are modified instead by a 20-carbon geranylgeranyl moiety. To determine the structural and functional basis for modification of proteins by a specific isoprenoid group, we have generated chimeric Ras proteins containing C-terminal CAAX sequences (CVLL and CAIL) from geranylgeranyl-modified proteins and a chimeric Krev-1 protein containing the H-Ras C-terminal CAAX sequence (CVLS). Our results demonstrate that both oncogenic Ras transforming activity and Krev-1 antagonism of Ras transforming activity can be promoted by either farnesyl or geranylgeranyl modification. Similarly, geranylgeranyl-modified normal Ras [Ras(WT)CVLL], when overexpressed, exhibited the same level of transforming activity as the authentic farnesyl-modified normal Ras protein. Therefore, farnesyl and geranylgeranyl moieties are functionally interchangeable for these biological activities. In contrast, expression of moderate levels of geranylgeranyl-modified normal Ras inhibited the growth of untransformed NIH 3T3 cells. This growth inhibition was overcome by coexpression of the mutant protein with oncogenic Ras or Raf, but not with oncogenic Src or normal Ras. The similar growth-inhibiting activities of Ras(WT)CVLL and the previously described Ras(17N) dominant inhibitory mutant suggest that geranylgeranyl-modified normal Ras may exert its growth-inhibiting action by perturbing endogenous Ras function. These results suggest that normal Ras function may specifically require protein modification by a farnesyl, but not a geranylgeranyl, isoprenoid.
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Affiliation(s)
- A D Cox
- La Jolla Cancer Research Foundation, California 92037
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121
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Ashby MN, King DS, Rine J. Endoproteolytic processing of a farnesylated peptide in vitro. Proc Natl Acad Sci U S A 1992; 89:4613-7. [PMID: 1584798 PMCID: PMC49133 DOI: 10.1073/pnas.89.10.4613] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Numerous eukaryotic proteins containing a carboxyl-terminal CAAX motif (C, cysteine; A, aliphatic amino acid; X, any amino acid) require a three-step posttranslational processing for localization and function. The a mating factor of Saccharomyces cerevisiae is one such protein, requiring cysteine farnesylation, proteolysis of the terminal three amino acids, and carboxyl methylation for biological activity. We have used farnesylated a-factor peptides to examine the proteolytic step in the maturation of CAAX-containing proteins. Three distinct carboxyl-terminal protease activities were found in yeast cell extracts that could remove the terminal three residues of a-factor. Two of the proteolytic activities were in cytosolic fractions. One of these activities was a PEP4-dependent carboxypeptidase that was sensitive to phenylmethylsulfonyl fluoride. The other cytosolic activity was PEP4-independent, sensitive to 1,10-phenanthroline, and effectively inhibited by an unfarnesylated a-factor peptide. In contrast, a protease activity in membrane fractions was unaffected by phenylmethylsulfonyl fluoride, 1,10-phenanthroline, or unfarnesylated a-factor peptide. Incubation of membrane preparations from either yeast or rat liver with a radiolabeled farnesylated a-factor peptide released the terminal three amino acids intact as a tripeptide, indicating that this reaction occurred by an endoproteolytic mechanism and that the enzyme most likely possesses a broad substrate specificity. The yeast endoprotease was not significantly affected by a panel of protease inhibitors, suggesting that the enzyme is novel. Zinc ion was shown to inhibit the endoprotease (Ki less than 100 microM). The specific activities of the a-factor carboxyl-terminal membrane endoprotease and methyltransferase clearly indicated that the proteolytic reaction was not rate-limiting in these processing reactions in vitro.
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Affiliation(s)
- M N Ashby
- Department of Molecular and Cell Biology, University of California, Berkeley 94720
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122
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123
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In vitro isoprenylation and membrane association of mouse rod photoreceptor cGMP phosphodiesterase alpha and beta subunits expressed in bacteria. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42466-0] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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124
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The Drosophila G protein gamma subunit gene (D-G gamma 1) produces three developmentally regulated transcripts and is predominantly expressed in the central nervous system. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42665-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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125
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Muntz KH, Sternweis PC, Gilman AG, Mumby SM. Influence of gamma subunit prenylation on association of guanine nucleotide-binding regulatory proteins with membranes. Mol Biol Cell 1992; 3:49-61. [PMID: 1550955 PMCID: PMC275501 DOI: 10.1091/mbc.3.1.49] [Citation(s) in RCA: 138] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Two approaches were taken to address the possible role of gamma-subunit prenylation in dictating the cellular distribution of guanine nucleotide-binding regulatory proteins. Prenylation of gamma subunits was prevented by site-directed mutagenesis or by inhibiting the synthesis of mevalonate, the precursor of cellular isoprenoids. When beta or gamma subunits were transiently expressed in COS-M6 simian kidney cells (COS) cells, the proteins were found in the membrane fraction by immunoblotting. Immunofluorescence experiments indicated that the proteins were distributed to intracellular structures in addition to plasma membranes. Replacement of Cys68 of gamma with Ser prevented prenylation of the mutant protein and association of the protein with the membrane fraction of COS cells. Immunoblotting results demonstrated that some of the beta subunits were found in the cytoplasm when coexpressed with the nonprenylated mutant gamma subunit. When Neuro 2A cells were treated with compactin to inhibit protein prenylation, a fraction of endogenous beta and gamma was distributed in the cytoplasm. It is concluded that prenylation facilitates association of gamma subunits with membranes, that the cellular location of gamma influences the distribution of beta, and that prenylation is not an absolute requirement for interaction of beta and gamma.
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Affiliation(s)
- K H Muntz
- Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center, Dallas 75235
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126
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Abstract
The prenylated proteins represent a newly discovered class of post-translationally modified proteins. The known prenylated proteins include the oncogene product p21ras and other low molecular weight GTP-binding proteins, the nuclear lamins, and the gamma subunit of the heterotrimeric G proteins. The modification involves the covalent attachment of a 15-carbon (farnesyl) or 20-carbon (geranylgeranyl) isoprenoid moiety in a thioether linkage to carboxyl terminal cysteine. The nature of the attached substituent is dependent on specific sequence information in the carboxyl terminus of the protein. In addition, prenylation entrains other posttranslational modifications forming a reaction pathway. In this article, we review our current understanding of the biochemical reactions involved in prenylation and discuss the possible role of this modification in the control of cellular functions such as protein maturation and cell growth.
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Affiliation(s)
- M Sinensky
- Eleanor Roosevelt Institute, Denver, CO 80206
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127
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128
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Takai Y, Kaibuchi K, Kikuchi A, Kawata M. Small GTP-binding proteins. INTERNATIONAL REVIEW OF CYTOLOGY 1992; 133:187-230. [PMID: 1577587 DOI: 10.1016/s0074-7696(08)61861-6] [Citation(s) in RCA: 275] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Y Takai
- Department of Biochemistry, Kobe University School of Medicine, Japan
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129
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Gierschik P. ADP-ribosylation of signal-transducing guanine nucleotide-binding proteins by pertussis toxin. Curr Top Microbiol Immunol 1992; 175:69-96. [PMID: 1628499 DOI: 10.1007/978-3-642-76966-5_4] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- P Gierschik
- Pharmakologisches Institut, Universität Heidelberg, FRG
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130
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Affiliation(s)
- R J Grand
- Department of Cancer Studies, Medical School, University of Birmingham, U.K
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131
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Kinsella BT, Erdman RA, Maltese WA. Posttranslational modification of Ha-ras p21 by farnesyl versus geranylgeranyl isoprenoids is determined by the COOH-terminal amino acid. Proc Natl Acad Sci U S A 1991; 88:8934-8. [PMID: 1924354 PMCID: PMC52625 DOI: 10.1073/pnas.88.20.8934] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
ras proteins undergo posttranslational modification by a 15-carbon farnesyl isoprenoid at a cysteine within a defined COOH-terminal amino acid motif; i.e., Cys-Ali-Ali-Ser/Met (where Ali represents an aliphatic residue). In other low molecular mass GTP-binding proteins, cysteines are modified by 20-carbon geranylgeranyl groups within a Cys-Ali-Ali-Leu motif. We changed the terminal Ser-189 of Ha-ras p21 to Leu-189 by site-directed mutagenesis and found that the protein was modified by [3H]geranylgeranyl instead of [3H]farnesyl in an in vitro assay. Gel-permeation chromatography of [3H]mevalonate-labeled hydrocarbons released from immunoprecipitated ras proteins overexpressed in COS cells indicated that Ha-ras p21(Leu-189) was also a substrate for 20-carbon isoprenyl modification in vivo. Additional steps in Ha-ras p21 processing, normally initiated by farnesylation, appear to be supported by geranylgeranylation, based on metabolic labeling of Ha-ras p21(Leu-189) with [3H]palmitate and its subcellular localization in a particulate fraction from COS cells. These observations indicate that the amino acid occupying the terminal position (Xaa) in the Cys-Ali-Ali-Xaa motif constitutes a key structural feature by which Ha-ras p21 and other proteins with ras-like COOH-terminal isoprenylation sites are distinguished as substrates for farnesyl- or geranylgeranyltransferases.
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Affiliation(s)
- B T Kinsella
- Weis Center for Research, Geisinger Clinic, Danville, PA 17822
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132
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Lorenz W, Inglese J, Palczewski K, Onorato JJ, Caron MG, Lefkowitz RJ. The receptor kinase family: primary structure of rhodopsin kinase reveals similarities to the beta-adrenergic receptor kinase. Proc Natl Acad Sci U S A 1991; 88:8715-9. [PMID: 1656454 PMCID: PMC52580 DOI: 10.1073/pnas.88.19.8715] [Citation(s) in RCA: 145] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
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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Affiliation(s)
- W Lorenz
- Howard Hughes Medical Institute, Department of Biochemistry, Duke University Medical Center, Durham, NC 27710
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133
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Goldstein J, Brown M, Stradley S, Reiss Y, Gierasch L. Nonfarnesylated tetrapeptide inhibitors of protein farnesyltransferase. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98441-3] [Citation(s) in RCA: 94] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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134
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Moores S, Schaber M, Mosser S, Rands E, O'Hara M, Garsky V, Marshall M, Pompliano D, Gibbs J. Sequence dependence of protein isoprenylation. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98729-6] [Citation(s) in RCA: 275] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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135
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Catty P, Deterre P. Activation and solubilization of the retinal cGMP-specific phosphodiesterase by limited proteolysis. Role of the C-terminal domain of the beta-subunit. EUROPEAN JOURNAL OF BIOCHEMISTRY 1991; 199:263-9. [PMID: 1649045 DOI: 10.1111/j.1432-1033.1991.tb16119.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The cGMP-specific phosphodiesterase (PDE) of vertebrate retinal rod outer segments (ROS) is a peripheral enzyme activated in vivo by transducin. In vitro artificial activation can be achieved using trypsin. This was described as resulting from degradation of the inhibitory gamma subunit (2 copies/PDE molecule), leaving intact the alpha beta catalytic core. It was, however, observed that trypsin could induce the release of PDE (or solubilization) from the ROS membranes before its activation [Wensel, T. G. & Stryer, L. (1986) Proteins Struct. Funct. Genet. 1, 90-99]. Studying the time course of this solubilization, we were able to purify a trypsin-solubilized PDE still completely inhibited (i.e. with its two gamma subunits bound). The tryptic solubilization of PDE is therefore complete before any functional degradation of the gamma subunits occurs. It was recently suggested that this solubilization could coincide with the cleavage of a C-terminal fragment of the alpha subunit, which can be labeled by methylation of a terminal cysteine residue [Ong, O. C., Ota, I. M., Clarke, S. & Fung, B. K. K. (1989) Proc. Natl Acad. Sci. USA 86, 9238-9242]. We present the following evidence indicating that the C-terminus of the PDE beta subunit is mainly responsible for PDE anchorage to the ROS membrane. (a) The trypsin-solubilized PDE alpha beta gamma 2 has intact blocked N-termini. (b) It is still methylated on PDE alpha. (c) The C-terminus of PDE beta can also be labeled by methylation and its tryptic cleavage coincides well with the PDE solubilization. (d) Sequential cleavage of the alpha and beta polypeptides can also be detected by high-resolution gel electrophoresis: the first cleavage appears on the beta subunit and is completed when cleavage of the alpha subunit begins. The time course for cleavage of the gamma subunits appears to be slower than for the beta subunit and comparable to that of the alpha subunit. Upon longer trypsinization, a 70-kDa polypeptide appears which seems to be a degradation product of PDE beta. Gel-filtration analysis, however, shows that this 70-kDa fragment does not dissociate from the catalytic core.
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Affiliation(s)
- P Catty
- Départment de Biologie Moléculaire et Structurale, Centre d'Etudes Nucléaires, Grenoble, France
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136
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Katayama M, Kawata M, Yoshida Y, Horiuchi H, Yamamoto T, Matsuura Y, Takai Y. The posttranslationally modified C-terminal structure of bovine aortic smooth muscle rhoA p21. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98947-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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137
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Yokoyama K, Goodwin GW, Ghomashchi F, Glomset JA, Gelb MH. A protein geranylgeranyltransferase from bovine brain: implications for protein prenylation specificity. Proc Natl Acad Sci U S A 1991; 88:5302-6. [PMID: 2052607 PMCID: PMC51860 DOI: 10.1073/pnas.88.12.5302] [Citation(s) in RCA: 179] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
A protein geranylgeranyltransferase (PGT) that catalyzes the transfer of a 20-carbon prenyl group from geranylgeranyl pyrophosphate to a cysteine residue in protein and peptide acceptors was detected in bovine brain cytosol and partially purified. The enzyme was shown to be distinct from a previously characterized protein farnesyltransferase (PFT). The PGT selectively geranylgeranylated a synthetic peptide corresponding to the C terminus of the gamma 6 subunit of bovine brain G proteins, which have previously been shown to contain a 20-carbon prenyl modification. Likewise, a peptide corresponding to the C terminus of human lamin B, a known farnesylated protein, selectively served as a substrate for farnesylation by the PFT. However, with high concentrations of peptide acceptors, both prenyl transferases were able to use either peptide as substrates and the PGT was able to catalyze farnesyl transfer. Among the prenyl acceptors tested, peptides and proteins with leucine or phenylalanine at their C termini served as geranylgeranyl acceptors, whereas those with C-terminal serine were preferentially farnesylated. These results suggest that the C-terminal amino acid is an important structural determinant in controlling the specificity of protein prenylation.
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Affiliation(s)
- K Yokoyama
- Department of Chemistry, University of Washington, Seattle, WA 98195
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138
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Tan E, Pérez-Sala D, Cañada F, Rando R. Identifying the recognition unit for G protein methylation. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)99074-5] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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139
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Kinsella B, Maltese W. rab GTP-binding proteins implicated in vesicular transport are isoprenylated in vitro at cysteines within a novel carboxyl-terminal motif. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)93008-5] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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140
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Carboxyl-terminal isoprenylation of ras-related GTP-binding proteins encoded by rac1, rac2, and ralA. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)92889-9] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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141
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Pérez-Sala D, Tan EW, Cañada FJ, Rando RR. Methylation and demethylation reactions of guanine nucleotide-binding proteins of retinal rod outer segments. Proc Natl Acad Sci U S A 1991; 88:3043-6. [PMID: 1901651 PMCID: PMC51380 DOI: 10.1073/pnas.88.8.3043] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Retinal transducin was previously shown to be farnesylated on its gamma subunit. This farnesylation reaction on a cysteine residue near the carboxyl terminus is followed by peptidase cleavage at the cysteine. Thus the modified cysteine becomes the carboxyl terminus. It is shown here that the free carboxyl group can be methylated by an S-adenosyl-L-methionine-dependent methyltransferase associated with the rod outer segment membranes. This process can be inhibited by S-adenosyl-L-homocysteine and sinefungin. Moreover, synthetic N-acetyl-S-farnesyl-L-cysteine, but not N-acetyl-L-cysteine, is a substrate for the enzyme. Rapid demethylation of N-acetyl-S-farnesyl-L-cysteine methyl ester can be observed in the membranes. Transducin is also enzymatically demethylated by the rod outer segment membranes. Moreover, the 23- to 29-kDa small G proteins are methylated and demethylated in this system. These data suggest that methylation/demethylation may play a regulatory role in visual signal transduction.
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Affiliation(s)
- D Pérez-Sala
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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142
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Simonds WF, Butrynski JE, Gautam N, Unson CG, Spiegel AM. G-protein beta gamma dimers. Membrane targeting requires subunit coexpression and intact gamma C-A-A-X domain. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(19)67601-5] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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143
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Hancock JF, Cadwallader K, Marshall CJ. Methylation and proteolysis are essential for efficient membrane binding of prenylated p21K-ras(B). EMBO J 1991; 10:641-6. [PMID: 2001678 DOI: 10.1002/j.1460-2075.1991.tb07992.x] [Citation(s) in RCA: 209] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Plasma membrane targeting of p21K-ras(B) requires a CAAX motif and a polybasic domain. The CAAX box directs a triplet of post-translational modifications: farnesylation, proteolysis of the AAX amino acids and methylesterification. These modifications are closely coupled in vivo. However, in vitro translation of mRNA in rabbit reticulocyte lysates produces p21K-ras(B) proteins which are arrested in processing after farnesylation. Intracellular membranes are then required both for proteolytic removal of the AAX amino acids and methylesterification of farnesylated p21K-ras(B). Binding of p21K-ras(B) to plasma membranes in vitro can then be shown to depend critically on AAX proteolysis and methylesterification since p21K-ras(B) which is farnesylated, but not methylated, binds inefficiently to membranes.
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Affiliation(s)
- J F Hancock
- Department of Haematology, Royal Free Hospital School of Medicine, London, UK
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