Secondary literature sources for GGL
The following references were automatically generated.
- Asano T, Morishita R, Ueda H, Kato K
- Selective association of G protein beta(4) with gamma(5) and gamma(12) subunits in bovine tissues.
- J Biol Chem. 1999; 274: 21425-9
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The beta and gamma subunits of G proteins are tightly bound under physiological conditions, and so far, seven beta and 11 gamma subunit isoforms have been found. The relative abilities of the beta and gamma subunits to associate with each other have been studied using transfected cell assays, in vitro translation and the yeast two-hybrid system, but have not been fully characterized in various tissues. In the present study, we demonstrated the selectivity of association of the beta with gamma isoforms in bovine tissues. Immunoprecipitation of betagamma complexes from tissue extracts with antibodies against various gamma subunits and subsequent analyses revealed that beta(4) associated with the gamma subunits with the following rank order of selectivity: gamma(5) > gamma(12) > gamma(2) > gamma(3), while beta(2) bound to gamma(2), gamma(3), and gamma(12) more selectively than to gamma(5). By contrast, beta(1) associated with all gamma subunits without significant selectivity. Analyses of purified betagamma complexes containing various gamma isoforms revealed beta subunit compositions similar to those found in the immunoprecipitates. Particular combinations of beta and gamma subunit isoforms may contribute to maintaining efficient and specific signal transduction mediated by G proteins.
- Kisselev OG, Kao J, Ponder JW, Fann YC, Gautam N, Marshall GR
- Light-activated rhodopsin induces structural binding motif in G protein alpha subunit.
- Proc Natl Acad Sci U S A. 1998; 95: 4270-5
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A large superfamily of transmembrane receptors control cellular responses to diverse extracellular signals by catalyzing activation of specific types of heterotrimeric GTP-binding proteins. How these receptors recognize and promote nucleotide exchange on G protein alpha subunits to initiate signal amplification is unknown. The three-dimensional structure of the transducin (Gt) alpha subunit C-terminal undecapeptide Gtalpha(340-350) IKENLKDCGLF was determined by transferred nuclear Overhauser effect spectroscopy while it was bound to photoexcited rhodopsin. Light activation of rhodopsin causes a dramatic shift from a disordered conformation of Gtalpha(340-350) to a binding motif with a helical turn followed by an open reverse turn centered at Gly-348, a helix-terminating C capping motif of an alphaL type. Docking of the NMR structure to the GDP-bound x-ray structure of Gt reveals that photoexcited rhodopsin promotes the formation of a continuous helix over residues 325-346 terminated by the C-terminal helical cap with a unique cluster of crucial hydrophobic side chains. A molecular mechanism by which activated receptors can control G proteins through reversible conformational changes at the receptor-G protein interface is demonstrated.
- Morishita R, Ueda H, Kato K, Asano T
- Identification of two forms of the gamma subunit of G protein, gamma10 and gamma11, in bovine lung and their tissue distribution in the rat.
- FEBS Lett. 1998; 428: 85-8
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Two forms of the gamma subunit of G protein were purified from bovine lung, and were identified as gamma10 and gamma11 by analyses of partial amino acid sequences and reactivity with specific antibodies. The N-terminal amino acid residue of gamma11 was an unmodified Pro2, and the purified gamma11 was freed from beta even under non-denaturing conditions. Western blots with specific antibodies against gamma10 and gamma11 showed that both gamma subunits are present in a variety of tissues in the rat, with a particular abundance of gamma11 in the platelets.
- Bruch RC, Medler KF, Tran HN, Hamlin JA
- G-protein beta gamma subunit genes expressed in olfactory receptor neurons.
- Chem Senses. 1997; 22: 587-92
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The expression of genes encoding G-protein beta gamma subunits was investigated in isolated olfactory receptor neurons from channel catfish. DNA sequencing of PCR products showed that the beta 1, beta 2, gamma 2 and gamma 3 genes were expressed in the neurons. Western blotting showed that at least three of these subunit proteins were expressed. This first analysis of the expression of beta gamma genes in olfactory receptor neurons suggests that these subunits may be involved in a variety of transduction events in these cells.
- Ong OC, Hu K, Rong H, Lee RH, Fung BK
- Gene structure and chromosome localization of the G gamma c subunit of human cone G-protein (GNGT2).
- Genomics. 1997; 44: 101-9
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Phototransduction in the vertebrate rod and cone photoreceptors is regulated by structurally homologous and yet distinct groups of signaling proteins. We have previously identified in bovine retinas a cone-specific G-protein gamma subunit (G gamma c, previously named G gamma b), which may play a key role in coupling the cone visual pigment to phosphodiesterase (O. C. Ong et al., 1995, J. Biol. Chem. 270:8495-8500). We report here the characterization of human G gamma c and its gene structure. Human G gamma c subunit shares a high degree of sequence identity with the corresponding bovine G gamma c isoform (85%) and human rod G gamma 1 (63%). The protein is specifically localized in cones, as indicated by immunohistochemical staining using anti-G gamma c antibodies. Nucleotide sequence analysis of the G gamma c gene (GNGT2) reveals a structure consisting of three exons and two introns, with the intron splice sites similar to that of the rod G gamma 1 gene (GNGT1). By using fluorescence in situ hybridization, we have further localized the human GNGT2 gene to chromosome 17q21. The elucidation of the G gamma c gene structure would facilitate the identification of genetic defects associated with cone degeneration.
- Ray K, Kunsch C, Bonner LM, Robishaw JD
- Isolation of cDNA clones encoding eight different human G protein gamma subunits, including three novel forms designated the gamma 4, gamma 10, and gamma 11 subunits.
- J Biol Chem. 1995; 270: 21765-71
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With the growing awareness that the G protein beta and gamma subunits directly regulate the activities of various enzymes and ion channels, the importance of identifying and characterizing these subunits is underscored. In this paper, we report the isolation of cDNA clones encoding eight different human gamma subunits, including three novel forms designated gamma 4, gamma 10, and gamma 11. The predicted protein sequence of gamma 4 shares the most identity (60-77%) with gamma 2, gamma 3, and gamma 7 and the least identity (38%) with gamma 1. The gamma 4 is modified by a geranylgeranyl group and is capable of interacting with both beta 1 and beta 2 but not with beta 3. The predicted protein sequence of gamma 10 shows only modest to low identity (35-53%) with the other known gamma subunits, with most of the differences concentrated in the N-terminal region, suggesting gamma 10 may interact with a unique subclass of alpha. The gamma 10 is modified by a geranylgeranyl group and is capable of interacting with beta 1 and beta 2 but not with beta 3. Finally, the predicted protein sequence of gamma 11 shows the most identity to gamma 1 (76% identity) and the least identity to the other known gamma (33-44%). Unlike most of the other known gamma subunits, gamma 11 is modified by a farnesyl group and is not capable of interacting with beta 2. The close resemblance of gamma 11 to gamma 1 raises intriguing questions regarding its function since the mRNA for gamma 11 is abundantly expressed in all tissues tested except for brain, whereas the mRNA for gamma 1 is expressed only in the retina where the protein functions in phototransduction.
- Fukada Y
- Prenylation and carboxylmethylation of G-protein gamma subunit.
- Methods Enzymol. 1995; 250: 91-105
- Asano T, Morishita R, Ohashi K, Nagahama M, Miyake T, Kato K
- Localization of various forms of the gamma subunit of G protein in neural and nonneural tissues.
- J Neurochem. 1995; 64: 1267-73
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For a study of the localization of various forms of the gamma subunit of G proteins, antibodies were raised in rabbits against peptides that corresponded to partial amino acid sequences of bovine gamma 2, gamma 3, gamma 5, and gamma 7. Affinity-purified antibodies against gamma 2, gamma 3, and gamma 5 reacted specifically with gamma 2, gamma 3, and gamma 5, respectively, but the antibody against gamma 7 reacted with gamma 2, gamma 3, and a novel gamma subunit, designated gamma S1, as well as with gamma 7. Because these antibodies reacted with the respective forms of the gamma subunit from rat brain, we investigated the localization of gamma subunits in the rat. gamma 2 and gamma 3 were abundant in all regions in the brain, whereas the concentration of gamma 5 and gamma 7 was relatively low with the single exception being a high concentration of gamma 7 in the striatum. The concentration of gamma 2 was consistently high during ontogenic development in the rat brain, whereas gamma 3 appeared about a week after birth and their concentrations then increased until a month after birth. In tissues other than the brain, gamma 3 was observed only in the pituitary gland, whereas gamma 2, gamma 5, and gamma 7 were found in a variety of tissues. In addition, most tissues contained relatively high concentrations of some other gamma subunit, which was detected with an antibody against a gamma 7-derived peptide and appeared to be gamma S1. Among cloned cells tested, gamma 3 was detected only in PC12 pheochromocytoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)
- Burstein SH, Debatis M, Subramanian A
- Cannabinoid photolabelling of a G-protein gamma-subunit in mouse peritoneal cells.
- Life Sci. 1995; 56: 1991-8
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Binding and photoactivation of a cannabinoid-derived ligand to intact mouse peritoneal cells has resulted in the labelling of a G-protein gamma-subunit. The assignment of structure is based on the product's physical characteristics and its ability to react with a polyclonal antiserum raised against the partial amino acid sequence for a gamma-subunit expressed in spleen cells. The binding characteristics of the ligand to the cells suggests that this gamma-subunit, and its associated alpha and beta subunits, are located in close proximity to one of the transmembrane cannabinoid receptors. Our findings further suggest a possible experimental approach to identifying receptor-G-protein complexes in intact cells.
- Meister M, Dietrich A, Gierschik P
- Identification of a three-amino-acid region in G protein gamma 1 as a determinant of selective beta gamma heterodimerization.
- Eur J Biochem. 1995; 234: 171-7
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Guanine-nucleotide-binding protein beta and gamma subunits belong to large protein families encompassing at least five and ten members, respectively, from mammalian cells. The formation of stable beta gamma heterodimers is a selective process determined by the primary sequences of both the beta and gamma subunit. For example, gamma 2 dimerizes with both beta 1 and beta 2, gamma 1 with beta 1, but not with beta 2. To identify the structural elements of gamma subunits relevant to the selectivity of beta gamma dimerization, we have used the baculovirus-insect cell-expression system to produce chimeric beta and gamma subunits and have studied their dimerization using an assay based on the ability of isoprenylation-resistant gamma subunit mutants to draw beta subunits into the cytosol and including sucrose density gradient analysis of soluble recombinant beta gamma dimers. The results show that replacement of three consecutive residues of gamma 1, Cys36-Cys37-Glu38, by the corresponding residues of gamma 2, Ala33-Ala34-Ala35, suffices to render the mutant gamma 1 subunit capable of forming heterodimers with beta 2. The ability of mutant gamma 1 subunits to dimerize with beta 2 does not correlate with the probability of the mutated region to participate in coiled-coil structures. The tripeptide region identified here as a critical determinant of the selectivity of beta gamma dimer formation is distinct from, but partially overlaps with, the region reported by Lee et al. [Lee, C., Murakami, T. & Simonds, W. F. (1995) J. Biol. Chem. 270, 8779-8784]. The results of this study, therefore, not only extend the region of gamma 1 selecting between beta 1 and beta 2 to the five-residue sequence between Cys36 and Phe40, but also argue against the notion that the hydrophobic terminal residue of this motif represents the key determinant of selective beta gamma interaction.
- Kalyanaraman S, Kalyanaraman V, Gautam N
- A brain-specific G protein gamma subunit.
- Biochem Biophys Res Commun. 1995; 216: 126-32
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Two different cDNAs for G protein gamma subunits have been isolated from mouse brain. One encodes a novel gamma subunit, gamma 4, the expression of which is detected only in brain. A fragment of this cDNA had been isolated previously. The other cDNA encodes gamma 3, a subunit type previously isolated from bovine brain. The primary structure of the gamma 3 subunit is conserved completely across species indicating that the diversity in the structure of the gamma subunits is of functional consequence. Moreover, gamma 2, gamma 3 and gamma 4, which are predominantly expressed in brain, are more homologous to each other than other gamma subunits, indicating that the G protein gamma subunits belong to distinct subfamilies similar to the alpha subunits.
- Yamauchi J, Kaziro Y, Itoh H
- Carboxyl terminal of G protein beta subunit is required for association with gamma subunit.
- Biochem Biophys Res Commun. 1995; 214: 694-700
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To investigate a complex formation of heterotrimeric G protein beta and gamma subunits, we constructed a deletion mutant which lacked the C-terminal WD40 repeating unit of beta 1 and cotransfected into HEK293 cells with gamma 2 which was tagged with FLAG-epitope. Co-immunoprecipitation assay indicated that the mutant beta 1 failed to associate with FLAG gamma 2. Furthermore, from the analysis of additional deletion mutants, the last 10 amino acids of C-terminal region of beta 1 were found to be necessary to associate with gamma 2. These results suggest that the C-terminal region, in addition to the N-terminal alpha-helical structure, of beta subunit may be involved in the beta gamma complex formation.
- Lee C, Murakami T, Simonds WF
- Identification of a discrete region of the G protein gamma subunit conferring selectivity in beta gamma complex formation.
- J Biol Chem. 1995; 270: 8779-84
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The identification of multiple G protein beta and gamma subunit subtypes suggests a potential diversity of beta gamma heterodimers, which may contribute to the specificity of signal transduction between receptors and effectors. The assembly of beta and gamma subtypes is selective. For example, gamma 1 can assemble with beta 1 but not with beta 2, whereas gamma 2 assembles with both beta isoforms. To identify the structural features of the beta and gamma subunits governing selectivity in heterodimer assembly, a series of nonisoprenylated chimeras of gamma 1 and gamma 2 was constructed, and their interaction with beta 1 and beta 2 was assessed by their ability to direct beta expression to the cytosol in cotransfected COS cells. All of the gamma 1/gamma 2 chimeras were capable of interacting with beta 1 as judged by the cotransfection assay. Chimeras containing gamma 2 sequence near the middle of the molecule between two conserved sequence motifs were capable of interacting as well with beta 2. Among 12 divergent residues in this region, it was found that replacement of three consecutive amino acids in gamma 1, Glu-Glu-Phe (residues 38-40), with the three corresponding amino acids of gamma 2, Ala-Asp-Leu (residues 35-37), conferred the ability to assemble with beta 2. The reciprocal chimera containing Glu-Glu-Phe in the context of gamma 2 failed to assemble with beta 2. The last residue of this triplet is occupied by a leucine in all known mammalian gamma subunits except gamma 1 and appears to be a key determinant of the ability of a gamma subunit to assemble with beta 2. This locus maps to a region of predicted alpha-helical structure in the gamma subunit, likely to represent a point of physical contact with the beta subunit.
- Rahmatullah M, Ginnan R, Robishaw JD
- Specificity of G protein alpha-gamma subunit interactions. N-terminal 15 amino acids of gamma subunit specifies interaction with alpha subunit.
- J Biol Chem. 1995; 270: 2946-51
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The existence of multiple alpha, beta, and gamma subunits raises questions regarding the assembly of particular G proteins. Based on the results of a previous study (Rahmatullah, M., and Robishaw, J. D. (1994) J. Biol. Chem. 269, 3574-3580), we hypothesized that the assembly of G proteins may be determined by the interactions of the more structurally diverse alpha and gamma subunits. This hypothesis was confirmed in the present study by showing striking differences in the abilities of the gamma 1 and gamma 2 subunits to interact with the alpha o subunit. Chimeras of the gamma 1 and gamma 2 subunits were used to delineate which region is responsible. Support for the importance of the N-terminal region of the gamma subunit comes from our observations that 1) the gamma 2 subunit and the gamma 211 chimera bound strongly to the alpha o-agarose matrix, but the gamma 1 subunit and the gamma 112 chimera bound weakly, if at all; 2) an N-terminal peptide made to the gamma 2 subunit blocked the binding of the gamma 211 chimera to the alpha o-agarose matrix; 3) both the gamma 211 chimera and the N-terminal peptide were able to partially protect the alpha o subunit against tryptic cleavage; and 4) the gamma 211 chimera, but not the gamma 112 chimera, supported ADP-ribosylation of the alpha o subunit.
- Wilcox MD et al.
- Bovine brain GO isoforms have distinct gamma subunit compositions.
- J Biol Chem. 1995; 270: 4189-92
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The gamma subunit composition of the major bovine brain Go and Gi proteins (GOA, GOB, GOC, Gi1, and Gi2) was characterized using antibodies against specific gamma isoforms. Each of the purified G protein heterotrimers contained a heterogeneous population of gamma subunits, and the profiles of the gamma subunits found with Gi1, Gi2, and GOA were similar. In contrast, each GO isoform had a distinct pattern of associated gamma subunits. These differences were surprising given that all three alpha O isoforms are thought to share a common amino-terminal sequence important for the binding of beta gamma dimers and that the alpha OA and alpha OC proteins may come from the same alpha O1 mRNA. The free alpha OA and alpha OC subunits had unique elution behaviors during MonoQ chromatography, compatible with differences in their post-translational processing. These results indicate that both the alpha and gamma subunit compositions of heterotrimers define the structure of an intact G protein. Furthermore, the exact subunit composition of G protein heterotrimers may depend upon regulated expression of different subunit isoforms or upon cellular processing of alpha subunits.
- Spring DJ, Neer EJ
- A 14-amino acid region of the G protein gamma subunit is sufficient to confer selectivity of gamma binding to the beta subunit.
- J Biol Chem. 1994; 269: 22882-6
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Heterotrimeric guanine nucleotide-binding proteins are important signaling molecules composed of an alpha, beta, and gamma subunit. The beta subunits must form dimers with gamma subunits to function. Several subtypes of beta and gamma have been identified, but not all combinations of beta and gamma subtypes can form dimers. For example, the gamma 2 subunit can form dimers with beta 1 and beta 2, but gamma 1 forms dimers only with beta 1, not with beta 2. Selective dimerization may play a role in the regulation of beta gamma dimer-mediated signal transduction. In order to identify the region of gamma responsible for selective dimer formation, a series of gamma 1/gamma 2 chimeras was constructed, transcribed, and translated in vitro. The ability of these gamma chimeras to form dimers with beta 1 and beta 2 was assayed by trypsin protection and chemical cross-linking. When amino acids 36-49 of gamma 1 were substituted for 33-46 of gamma 2, the chimera behaved like gamma 1 and dimerized only with beta 1; the reciprocal chimera, in which 14 residues from gamma 2 were substituted for the corresponding amino acids of gamma 1, behaved like gamma 2 and interacted with both beta 1 and beta 2. This 14-amino acid region was sufficient for gamma 1 to discriminate between the beta subunits. All gamma chimeras were functional because they were able to interact with beta 1, which is capable of forming dimers with both gamma 1 and gamma 2. All dimers of chimeric gamma subunits plus beta 1 were able to interact with purified alpha o subunit, indicating that beta gamma dimers containing chimeric gamma molecules were capable of interacting with an appropriate third molecule. This lays the foundation for using these gamma chimeras to study selective dimer interactions with various effectors and receptors.
- Spickofsky N et al.
- Biochemical analysis of the transducin-phosphodiesterase interaction.
- Nat Struct Biol. 1994; 1: 771-81
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In vertebrate rod cells, the activated alpha-subunit of rod transducin interacts with the gamma (regulatory) subunits of phosphodiesterase to disinhibit the catalytic subunits. A 22-amino acid long region of rod transducin involved in phosphodiesterase activation has recently been identified. We have used peptides from this region of rod transducin and from several other G protein alpha-subunits to study the nature and specificity of the G protein alpha-effector interaction. Although peptides derived from rod transducin, cone transducin and gustducin are similar, only the rod peptide is capable of activating rod phosphodiesterase. Using substituted peptides we have identified five residues on one exposed face of rod transducin as important to phosphodiesterase activation. These results disagree with previous models which propose that loop regions of rod transducin interact with phosphodiesterase gamma.
- Robishaw JD, Balcueva EA
- Preparation, characterization, and use of antibodies with specificity for G-protein gamma subunits.
- Methods Enzymol. 1994; 237: 498-509
- Morishita R, Kato K, Asano T
- A brain-specific gamma subunit of G protein freed from the corresponding beta subunit under non-denaturing conditions.
- FEBS Lett. 1994; 337: 23-6
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It has generally been accepted that the beta and gamma subunits of G proteins are tightly associated and can only be dissociated under denaturing conditions. However, one form of the gamma subunit, free of the beta subunit, was isolated under non-denaturing conditions during the purification of beta gamma complexes from bovine brain. Amino acid sequence analysis revealed that the N-terminus of this gamma subunit was not blocked and its sequence was identical to that of a brain-specific gamma subunit, gamma 3. Among three forms of gamma subunits observed in bovine brain (gamma 2, gamma 3 and gamma 7), gamma 3 was the only form that was not modified at the N-terminus. Although the physiological significance of the free form of gamma 3 is not clear, these results suggest that N-terminal modification of gamma subunits may be important for interaction with beta subunits.
- Matsuda T et al.
- Characterization of interactions between transducin alpha/beta gamma-subunits and lipid membranes.
- J Biol Chem. 1994; 269: 30358-63
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The gamma-subunits of heterotrimeric guanine nucleotide-binding regulatory proteins (G-proteins) are isoprenylated and alpha-carboxyl methylated at their COOH-terminal cysteine residues. These modifications are necessary for membrane attachment of the beta gamma complex, but a requirement of an additional factor has been proposed for the stable binding. We explored a possible contribution of the blocked amino terminus of beta-subunits of bovine photoreceptor G-protein, transducin (T alpha/T beta gamma = Gt alpha/beta 1 gamma 1), and of three beta gamma complexes (beta 1 gamma 2, beta 1 gamma 3, and beta 1 gamma 7) purified from bovine brains. Structural analyses revealed that every beta 1-subunit has an N-acetylated serine, which is unlikely to contribute to the membrane association. Since neither protease nor heat treatment of photoreceptor membranes affected the membrane binding of T beta gamma, it seems unlikely that rhodopsin (or other membrane proteins) serves as an anchor protein for accepting T beta gamma. In fact, T beta gamma bound to phospholipid large unilamellar vesicles (LUVs), of which the polar head groups strongly influenced the binding: T beta gamma alone showed 2-fold higher binding for negatively charged phosphatidylserine-LUVs than for neutral phosphatidylcholine (PC)-LUVs, while the affinity of T alpha/T beta gamma complex for the phosphatidylserine-LUVs was lower than that for the PC-LUVs. These results indicate that 1) an ionic interaction between T beta gamma and membrane surface plays an important role in the stable membrane association, and 2) the domain(s) of T beta gamma responsible for the association would be different between trimeric and dissociated states. We also found that synthetic peptides corresponding to the COOH-terminal region of T gamma inhibited T alpha-T beta gamma interaction only when the peptides were isoprenylated. This suggests that the isoprenyl moiety is located at the contact site between the subunits, not at the membrane-binding domain, when T beta gamma is complexed with T alpha.
- Sohma H, Hashimoto H, Hiraike N, Ohguro H, Akino T
- Identification of a novel gamma-subunit from bovine brain GTP binding regulatory proteins (Gi/o).
- Biochem Biophys Res Commun. 1993; 190: 849-56
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Heterogeneity of the gamma-subunit of G proteins has been demonstrated by cDNA cloning and by partial sequence analyses. We have isolated two intact beta gamma-subunit isoforms from bovine brain Gi/o mixture, in which only gamma subunits are distinct (Sohma, H., et al. (1992) Biochem. Biophys. Res. Commun. 184, 175-182). In this study, we isolated the gamma-subunit isoforms, gamma-I and gamma-II, and examined their amino acid sequences. Both gamma-I and gamma-II had blocked N-terminal amino acid residues, and the terminal amino acids of both were able to be truncated by an acylamino-acid-releasing enzyme. Gamma-I seemed to be identical with the gamma-subunit reported elsewhere, while the gamma-II appeared to be a novel protein. Antibodies to synthetic peptides based on the part of the amino acid sequences of gamma-I and gamma-II reacted specifically to gamma-I and gamma-II, respectively.
- Kisselev O, Gautam N
- Specific interaction with rhodopsin is dependent on the gamma subunit type in a G protein.
- J Biol Chem. 1993; 268: 24519-22
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Interaction with a receptor is the first step in the process of signal transduction by heterotrimeric (alpha beta gamma) G proteins. We have examined the role of the G protein gamma subunit in interaction between a receptor (rhodopsin) and a G protein, transducin (Gt). We have obtained recombinant beta gamma complexes containing the same beta subunit but three different gamma subunit types by expressing them in the baculovirus/insect cell system. We show that the different recombinant beta gamma complexes interact equally well with the alpha subunit of transducin (alpha t) but only the gamma subunit specific to rod photoreceptors (gamma 1) is able to support interaction of alpha t with rhodopsin. This indicates a direct role for the G protein gamma subunits, which are a family of proteins with diverse structures, in conferring specificity to receptor-G protein interaction.
- Jaffe LA, Gallo CJ, Lee RH, Ho YK, Jones TL
- Oocyte maturation in starfish is mediated by the beta gamma-subunit complex of a G-protein.
- J Cell Biol. 1993; 121: 775-83
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The stimulation of meiotic maturation of starfish oocytes by the hormone 1-methyladenine is mimicked by injection of beta gamma subunits of G-proteins from either retina or brain. Conversely, the hormone response is inhibited by injection of the GDP-bound forms of alpha i1 or alpha t subunits, or by injection of phosducin; all of these proteins should bind free beta gamma. alpha-subunit forms with reduced affinity for beta gamma (alpha i1 or alpha t bound to hydrolysis-resistant GTP analogs, or alpha i1-GMPPCP treated with trypsin to remove the amino terminus of the protein) are less effective inhibitors of 1-methyladenine action. These results indicate that the beta gamma subunit of a G-protein mediates 1-methyladenine stimulation of oocyte maturation.
- Ohguro H, Fukada Y, Akino T
- Structure and function of gamma-subunit of photoreceptor G-protein (transducin).
- Comp Biochem Physiol B. 1991; 100: 433-8
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1. The gamma-subunit of the vertebrate photoreceptor GTP-binding protein (transducin) is S-farnesylated at the C-terminal cysteine residue, with a part of the residue being methyl-esterified at the alpha-carboxyl group. 2. Functionally, the modified cysteine residue is implicated in efficient coupling of the alpha- and beta gamma-subunits, and indispensible for expressing GTP-binding activity. 3. Similar modifications, isoprenylation and methyl-esterification of the C-terminal cysteine residue have been found in a variety of proteins involved in signal transduction and growth regulation processes. However, it seems likely that the physiological roles of the modifications are different for the various proteins.
- Lai RK, Perez-Sala D, Canada FJ, Rando RR
- The gamma subunit of transducin is farnesylated.
- Proc Natl Acad Sci U S A. 1990; 87: 7673-7
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Protein prenylation with farnesyl or geranylgeranyl moieties is an important posttranslational modification that affects the activity of such diverse proteins as the nuclear lamins, the yeast mating factor mata, and the ras oncogene products. In this article, we show that whole retinal cultures incorporate radioactive mevalonic acid into proteins of 23-26 kDa and one of 8 kDa. The former proteins are probably the "small" guanine nucleotide-binding regulatory proteins (G proteins) and the 8-kDa protein is the gamma subunit of the well-studied retinal heterotrimeric G protein (transducin). After deprenylating purified transducin and its subunits with Raney nickel or methyl iodide/base, the adducted prenyl group can be identified as an all-trans-farnesyl moiety covalently linked to a cysteine residue. Thus far, prenylation reactions have been found to occur at cysteine in a carboxyl-terminal consensus CAAX sequence, where C is the cysteine, A is an aliphatic amino acid, and X is undefined. Both the alpha and gamma subunits of transducin have this consensus sequence, but only the gamma subunit is prenylated. Therefore, the CAAX motif is not necessary and sufficient to direct prenylation. Finally, since transducin is the best understood G protein, both structurally and mechanistically, the discovery that it is farnesylated should allow for a quantitative understanding of this post-translational modification.
