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1.
The involvement of multiple G-proteins in parathyroid hormone regulation of acid production was demonstrated in a highly enriched osteoclast population. Osteoclasts were isolated from the endosteum of 2.5 to 3-week-old chicken tibia using sequential enzymatic digestion. Single cell analysis of acid production was accomplished using microscope photometry and vital staining with acridine orange, a hydrogen ion concentration sensitive fluorescent dye. Lithium chloride, an uncoupler of G-proteins from their respective receptors, blocked parathyroid hormone stimulated production of acid. Cholera toxin, which permanently activates Gs-proteins, mimicked PTH stimulation. Pertussis toxin, which prevents receptor interaction with Gi- and Go-proteins, blocked both 10 8 M and 10 11 M PTH stimulated acid production, suggesting that the pertussis toxin-sensitive G-protein is utilized at both PTH concentrations. Immunoblots of osteoclast plasma membrane proteins, using a panel of antibodies generated against specific G-protein α subunits, revealed a 48 kDa Gsα, a 41 Goα, a 34 kDa Giα-3, and a unique 68 kDa Gα subunit, with the 41 kDa and 34 kDa bands being the most intense. Immunoblots of osteoblast plasma membrane proteins had a substantially different profile with the most intense bands being a Gsα (48 kDa) and a Goα (36 and 38 kDa). The studies suggest the utilization of at least two different G-proteins in the parathyroid hormone regulation of acid formation by osteoclasts, a Gs and a pertussis toxin-sensitive G-protein (Go and/or Giα-3). J. Cell. Biochem. 64:161–170. © 1997 Wiley-Liss, Inc. 相似文献
2.
The fungus Arthrobotrys dactyloides produces specialized constricting rings to trap and then consume nematodes. The signal transduction pathway involved in the
nematode-trapping process was examined. Mastoparan, an activator of G-protein, had a stimulatory effect on the inflation of
ring cells, whereas a G-protein inhibitor, pertussis toxin, prevented ring-cell expansion. The 40-kDa Gα of heterotrimeric G-proteins was specifically ADP-ribosylated by pertussis toxin. Using an antibody specific to the 35-kDa
subunit Gβ, we showed that immunogold-labeled Gβ was more concentrated in ring cells than in the hyphae. In the absence of nematodes, the rings could be inflated by either
pressurizing the culture in a syringe, raising intracellular Ca2+ concentrations, or adding warm water. We used these methods to reveal differences in responses to antagonists. The results
support a model in which the pressure exerted by a nematode on the ring activates G-proteins in the ring cells. The activation
leads to an increase in cytoplasmic Ca2+, activation of calmodulin, and finally the opening of water channels. The ring cells expand to constrict the ring and thus
immobilize the nematode.
Received: 13 April 2000 / Accepted: 22 June 2000 相似文献
3.
Clark GD Zorumski CF McNeil RS Happel LT Ovella T McGuire S Bix GJ Swann JW 《Neurochemical research》2000,25(5):603-611
In most nonneural systems, platelet-activating factor (PAF) receptor effects are mediated by G-proteins that are often pertussis toxin-sensitive. The activation of pertussis toxin-sensitive G-proteins linked to PAF receptors results in the mobilization of intracellular calcium, at least in part, through the second messenger inositol triphosphate. We have sought to determine if a pertussis toxin-sensitive G-protein is involved in the PAF receptor-mediated phenomena of growth cone collapse and of synaptic enhancement in primary neuronal culture. Using infrared differential interference contrast microscopy and patch-clamp recording techniques, pertussis toxin, but not the inactive B oligomer of the toxin, was found to block both the growth cone collapse and the enhanced synaptic release of excitatory transmitter induced by a nonhydrolyzable PAF receptor agonist, making it likely that Go, Gq, or Gi is the G-protein transducer of PAF receptors in primary neurons. We believe that PAF acts directly on neuronal receptors, which are linked to pertussis toxin-sensitive G-proteins, on the tips of developing neurites, and on presynaptic nerve terminals, leading to growth cone collapse and enhanced synaptic release of transmitter. 相似文献
4.
Ovarian follicles of Hyalophora cecropia stopped accumulating [35S]vitellogenin when incubated in pertussis toxin, a Gi protein inactivator. At a cellular level, the responses to pertussis toxin resembled those described earlier to cell-permeant analogs of cyclic AMP. They included accelerated 36Cl– exchange, 86Rb+ uptake, and follicle cell swelling, which in turn resulted in a loss of epithelial patency. A 34% rise in follicular cAMP content accompanied these changes. In particulate fractions of follicle homogenates, pertussis toxin catalyzed the ADP-ribosylation of a polypeptide that resolved at 39 kDa in SDS-PAGE; rabbit antibodies to a C-terminal decapeptide common to 39 kDa mammalian Giα-3 and Goα were bound in immunoblots at this same location. The findings suggest that a pertussis toxin-sensitive Gα facilitates epithelial patency during vitellogenesis by suppressing cAMP levels. When follicles are released from this restraint, either experimentally with pertussis toxin or by progressing to the next phase in their normal program of development, cAMP levels rise and vitellogenesis terminates. Arch. Insect Biochem. Physiol. 39:36–45, 1998. © 1998 Wiley-Liss, Inc. 相似文献
5.
Andreas Janshoff Claudia Steinem Manfred Sieber A. el Bayâ Marcus Alexander Schmidt H.-J. Galla 《European biophysics journal : EBJ》1997,26(3):261-270
The binding of cholera toxin, tetanus toxin and pertussis toxin to ganglioside containing solid supported membranes has been
investigated by quartz crystal microbalance measurements. The bilayers were prepared by fusion of phospholipid-vesicles on
a hydrophobic monolayer of octanethiol chemisorbed on one gold electrode placed on the 5 MHz AT-cut quartz crystal. The ability
of the gangliosides GM1, GM3, GD1a, GD1b, GT1b and asialo-GM1 to act as suitable receptors for the different toxins was tested by measuring the changes of quartz resonance frequencies.
To obtain the binding constants of each ligand-receptor-couple Langmuir-isotherms were successfully fitted to the experimental
adsorption isotherms. Cholera toxin shows a high affinity for GM1 (Ka = 1.8 ⋅ 108M–1), a lower one for asialo-GM1 (Ka = 1.0 ⋅ 107 M–1) and no affinity for GM3. The C-fragment of tetanus toxin binds to ganglioside GD1a, GD1b and GT1b containing membranes with similar affinity (Ka∼106 M–1), while no binding was observed with GM3. Pertussis toxin binds to membranes containing the ganglioside GD1a with a binding constant of Ka = 1.6 ⋅ 106 M–1, but only if large amounts (40 mol%) of GD1a are present. The maximum frequency shift caused by the protein adsorption depends strongly on the molecular structure of
the receptor. This is clearly demonstrated by an observed maximum frequency decrease of 99 Hz for the adsorption of the C-fragment
of tetanus toxin to GD1b. In contrast to this large frequency decrease, which was unexpectedly high with respect to Sauerbrey's equation, implying
pure mass loading, a maximum shift of only 28 Hz was detected after adsorption of the C-fragment of tetanus toxin to GD1a.
Received: 14 January 1997 / Accepted: 15 April 1997 相似文献
6.
《Journal of receptor and signal transduction research》2013,33(4-5):313-329
AbstractSite specific antisera against a synthetic peptide corresponding to the sequence 3–17 of Gαi2 have been raised and the specificity examined using purified homogeneous Go, Gi2 and Gi containing a 41 kDa α-subunit. The distribution of Gαi2 was investigated in plasma membranes from different tissues and cells and compared to the distribution of Gαo and other pertussis toxin sensitive Gα. Considerable amounts of Gαio were found in endocrine tissue especially in membranes from the adrenal and thyroid, in leucocytes and platelets where it constitutes the major, if not only, pertussis toxin-sensitive Gα, as well as in some cell lines (C6, NG 108–15, S49 cyc?); erythrocytes contained a 41 kDa Gαi which was different from Gαo. Gαo was present abundantly in nervous tissue, adrenal medulla and cortex but also found in low amounts in other membranes except for lung, liver and blood cells. Subcellular fractionaltion of cardiac ventricular muscle demonstrated the presence of Gαo and low amounts of Gαi2 in sarcolemma, but only 41kDa Gαi was present in sarcoplasmic reticulum. The importance of the distinct distribution in terms of signal transduction is discussed. 相似文献
7.
Chakraborti S Mandal A Das S Chakraborti T 《Molecular and cellular biochemistry》2005,280(1-2):107-117
Treatment of bovine pulmonary artery smooth muscle with the O2•− generating system hypoxanthine plus xanthine oxidase stimulated MMP-2 activity and PKC activity; and inhibited Na+ dependent Ca2+ uptake in the microsomes. Pretreatment of the smooth muscle with SOD (the O2•− scavenger) and TIMP-2 (MMP-2 inhibitor) prevented the increase in MMP-2 activity and PKC activity, and reversed the inhibition
of Na+ dependent Ca2+ uptake in the microsomes. Pretreatment with calphostin C (a general PKC inhibitor) and rottlerin (a PKCδ inhibitor) prevented
the increase in PKC activity and reversed O2•− caused inhibition of Na+ dependent Ca2+ uptake without causing any change in MMP-2 activity in the microsomes of the smooth muscle. Treatment of the smooth muscle
with the O2•− generating system revealed, respectively, 36 kDa RACK-1 and 78 kDa PKCδ immunoreactive protein profile along with an additional
38 kDa immunoreactive fragment in the microsomes. The 38 kDa band appeared to be the proteolytic fragment of the 78 kDa PKCδ
since pretreatment with TIMP-2 abolished the increase in the 38 kDa immunoreactive fragment. Co-immunoprecipitation of PKCδ
and RACK-1 demonstrated O2•− dependent increase in PKCδ-RACK-1 interaction in the microsomes. Immunoblot assay elicited an immunoreactive band of 41 kDa
Giα in the microsomes. Treatment of the smooth muscle tissue with the O2•− generating system causes phosphorylation of Giα in the microsomes and pretreatment with TIMP-2 and rottlerin prevented the phosphorylation. Pretreatment of the smooth muscle
tissue with pertussis toxin reversed O2•− caused inhibition of Na+ dependent Ca2+ uptake without affecting the protease activity and PKC activity in the microsomes. We suggest the existence of a pertussis
toxin sensitive G protein mediated mechanism for inhibition of Na+ dependent Ca2+ uptake in microsomes of bovine pulmonary artery smooth muscle under O2•− triggered condition, which is regulated by PKCδ dependent phosphorylation and sensitive to TIMP-2 for its inhibition. (Mol
Cell Biochem xxx: 107–117, 2005) 相似文献
8.
《Life sciences》1992,50(5):PL19-PL24
The mechanism by which the inhibitory effect of d-ala2-met-enkephalinamide (DALA) on lacrimal acinar adenylyl cyclase is exerted was assessed in membrane preparations by a cAMP protein binding assay. Inhibition by the analogue was GTP-dependent with a significant enhancement of the inhibitory effect by GTP. While pretreatment of membranes with either cholera or pertussis toxin resulted in stimulation of adenylyl cyclase activity, modification of the Giα subunit by pertussis-toxin catalyzed ADP-ribosylation did not effect the hormonal inhibition of adenylyl cyclase. Incubation of membranes with manganese, however, prevented the inhibitory action of DALA in addition to enhancing basal and forskolin-stimulated adenylyl cyclase activity. The results suggest that the inhibitory effect of DALA in lacrimal acinar cells is exerted via a mechanism other than pertussis-toxin sensitive coupling of the receptor to adenylyl cyclase through Gi. The mechanism may be effected through a pertussis-toxin insensitive G protein, through an interaction with Gi that is pertussis-toxin insensitive, or through an interaction with the catalytic subunit of adenylyl cyclase. 相似文献
9.
Adenosine Release and Uptake in Cerebellar Granule Neurons Both Occur via an Equilibrative Nucleoside Carrier that Is Modulated by G Proteins 总被引:6,自引:3,他引:3
M. I. Sweeney 《Journal of neurochemistry》1996,67(1):81-88
Abstract: There is debate about the mechanisms mediating adenosine release from neurons. In this study, the release of adenosine evoked by depolarizing cultured cerebellar granule neurons with 50 mM K+ was inhibited by 49 ± 7% in Ca2+-free medium. The remaining release was blocked by dipyridamole (IC50 = 6.4 × 10?8M) and nitrobenzylthioinosine (IC50 = 3.6 × 10?8M), inhibitors of adenosine uptake. Ca2+-dependent release was reduced by 78 ± 9% following a 21-h pretreatment of the cells with pertussis toxin, which ADP-ribosylates Gi/Go G proteins, thereby preventing their dissociation. The nucleoside transporter-mediated component of K+-induced adenosine release also was inhibited by 62 ± 8% by pertussis toxin and was potentiated by 78 ± 11% following cholera toxin treatment, which permanently activates Gs. Uptake of [3H]adenosine into cultured cerebellar granule neurons over a 10-min period was not dependent on extracellular Na+ but was reduced by dipyridamole (IC50 = 3.2 × 10?8M) and nitrobenzylthioinosine (IC50 = 2.6 × 10?8M). Thus, adenosine uptake likely occurs via the same transporter mediating Ca2+-independent adenosine release. Adenosine uptake was potentiated by cholera toxin pretreatment (152 ± 15% of control), but pertussis toxin had no statistically significant effect. It is possible that Gs, Gi/Go, or free Gβγ dimer modulate the equilibrative, inhibitor-sensitive nucleoside carrier to enhance adenosine transport. 相似文献
10.
GAP-43 and Go are peripheral membrane proteins enriched in neuronal growth cone. GAP-43 was highly purified from bovine cerebral cortex
and myristoylated Goα was highly purified from Escherichia coli cotransformed with pQE60 Goα and pBB131 (NMT). GAP-43 stimulated GTPγS binding to Goα and the stimulation effect was dependent on concentration of GAP-43. Protein-protein binding experiments using CaM-Sepharose
affinity media revealed that Goα GDP bound GAP-43 directly to form intermolecular complex. This interaction induced conformational change of Goα. In the presence of GAP-43, fluorescence spectrum of Goα GDP blue shifted 4 nm; fluorescence intensity increased 35.3% and apparent quenching constant (Ksv) increased from (1.1
±0.22) ×105 to (4.1±0.43) × 105 (M−1). However, no obvious changes of fluorescence spectra of Goα GTPγS were observed in the absence or presence of GAP-43. Our results indicated that GAP-43 induced conformational change
of Goα GDP so as to accelerate GDP release and subsequent GTPγS binding, which activates G proteins to trigger signal transduction
and amplification. These results provided insights into understanding the function of G proteins in coupling between receptors
and effectors and the key role of GDP/GTP exchange mode in GTPase cycle. 相似文献
11.
The lipoglycoproteins of the WNT family act on seven transmembrane-spanning Class Frizzled receptors. Here, we show that WNT-5A evokes a proliferative response in a mouse microglia-like cell line (N13), which is sensitive to pertussis toxin, thus implicating the involvement of heterotrimeric G proteins of the Gi/o family. We continue to show that WNT-5A stimulation of N13 membranes and permeabilized cells evokes the exchange of GDP for GTP of pertussis toxin-sensitive G proteins employing [γ-35S]GTP assay and activity state-specific antibodies to GTP-bound Gi proteins. Our functional analysis of the PTX-sensitivity of WNT-induced G protein activation and PCR analysis of G protein and FZD expression patterns suggest that WNT-5A stimulation leads to the activation of Gi2/3 proteins in N13 cells possibly mediated by FZD5, the predominant FZD expressed. In summary, we provide for the first time molecular proof that WNT-5A stimulation results in the activation of heterotrimeric Gi2/3 proteins in mammalian cells with physiological protein stochiometry. 相似文献
12.
Other than the fact that the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel can be activated by cAMP dependent kinase (PKA), little is known about the signal transduction pathways regulating
CFTR. Since G-proteins play a principal role in signal transduction regulating several ion channels [4, 5, 9], we sought to
test whether G-proteins control CFTR Cl− conductance (CFTR G
Cl
) in the native sweat duct (SD). We permeabilized the basolateral membrane with α-toxin so as to manipulate cytosolic nucleotides.
We activated G-proteins and monitored CFTR G
Cl
activity as described earlier [20, 23, 25]. We now show that activating G-proteins with GTP-γ-S (100 μm) also activates CFTR G
Cl
in the presence of 5 mm ATP alone (without exogenous cAMP). GTP-γ-S increased CFTR G
Cl
by 44 ± 20 mS/cm2 (mean ±se; n= 7). GDP (10 mm) inhibited G-protein activation of CFTR G
Cl
even in the presence of GTP-γ-S. The heterotrimeric G-protein activator (AlF4
−) in the cytoplasmic bath activated CFTR G
Cl
(increased by 51.5 ± 9.4 mS/cm2 in the presence of 5 mm ATP without cAMP, n= 6), the magnitude of which was similar to that induced by GTP-γ-S. Employing immunocytochemical-labeling techniques, we
localized Gαs, Gαi, Gαq, and Gβ at the apical membranes of the sweat duct. Further, we showed that the mutant CFTR G
Cl
in ducts from cystic fibrosis (CF) subjects could be partially activated by G-proteins. The magnitude of mutant CFTR G
Cl
activation by G-proteins was smaller as compared to non-CF ducts but comparable to that induced by cAMP in CF ducts. We conclude
that heterotrimeric G-proteins are present in the apical membrane of the native human sweat duct which may help regulate salt
absorption by controlling CFTR G
Cl
activity.
Received: 9 June 2000/Revised: 5 October 2000 相似文献
13.
Albrecht Piiper Danuta Stryjek-Kaminska Ralph Gebhardt Stefan Zeuzem 《Journal of cellular physiology》1996,167(1):52-59
Signal transduction of fibroblast growth factor (FGF) receptors is known to involve tyrosine phosphorylation of several substrates, including Grb2, phospholipase C-γ, and phosphatidylinositol 3-kinase, whereas the role of G-proteins in FGF receptor signaling is controversial. In the present study we investigated the role of G-proteins in FGF receptor signaling in rat pancreatic acini. Immunological analysis revealed the presence of FGF receptor and phospholipase C-γ1 in rat pancreatic acini. Both basic fibroblast growth factor (FGF-2) and guanosine 5′-(γ-O-thio)triphosphate (GTPγS) caused an increase in inositol 1,4,5-trisphosphate (1,4,5-IP3) production and amylase release. Combined stimulation of the acini with GTPγS and FGF-2 led to a decrease of these responses as compared to the effect of the single substances. When pancreatic acini were preincubated with FGF-2 (1 nM) or vehicle (water) ADP-ribosylation of the α-subunit of Gi-type G-proteins by pertussis toxin was reduced in membranes prepared from FGF-2 pretreated acini as compared to control acini, suggesting functional interaction of FGF receptors with Gi-proteins. Pretreatment of acini with pertussis toxin which inhibits Gi-type G-proteins abolished the inhibitory effect of GTPγS on FGF-induced 1,4,5-IP3 production and amylase release, whereas the stimulatory effects of FGF-2 and GTPγS on these parameters remained unchanged. In conclusion, these results show communication of FGF receptors and Gi-type G-proteins and that Gi-type G-proteins exert an inhibitory influence on FGF-induced activation of phosphoinositide-specific phospholipase C in pancreatic acinar cells. © 1996 Wiley-Liss, Inc. 相似文献
14.
Claude Sauvage Jean-François Rumigny Michel Maitre 《Molecular and cellular biochemistry》1991,107(1):65-77
Summary Three G proteins from human brain membranes were purified to near homogeneity by conventional techniques including preparative
electrophoresis. These G proteins were characterized by their ability to bind GTP, GDP and GTP analogs. Two of these proteins
have molecular weights of 50,000 (G50) and 36,000 (G36), as determined on SDS-gels. G36 was ADP-ribosylated by pertussis toxin. Thus, G50 could represent a Gsα subunit, whereas G36 could be Giα or Goα. G50 was phosphorylated by cAMP dependent protein kinase and protein kinase C. G36 was phosphorylated by a protein kinase independent of calcium and phospholipid, a proteolytic product of protein kinase C,
analogous to protein kinase M. Phosphorylation of G36 by this protein kinase induced a dramatic decrease in its GTPase activity. The third G protein, of molecular weight 22,000
probably belongs to the group of monomeric G proteins possessing functional similarities withras gene products. The regulation of G proteins involving calcium-dependent and independent pathways is delineated. 相似文献
15.
Abstract: The identity and role of G proteins in coupling adenosine receptors to effectors have been studied to a limited degree. We have identified the G proteins whose GTPase activity is stimulated by adenosine receptor agonists in neuronal membranes. (R)-Phenylisopropyladenosine, 2-chloroadenosine, and N-ethylcarboxamideadenosine produced a concentration-dependent stimulation of GTPase. At 10?5M, the increase above basal GTPase in frontal cortex was 25 ± 4, 20 ± 3, and 8 ± 1%, respectively, and in the cerebellum 55 ± 2, 41 ± 4, and 22 ± 2%, respectively. The effects of (R)-phenylisopropyladenosine and 2-chloroadenosine were inhibited by (1) A1 antagonists (76–96% reduction), (2) pretreatment with pertussis toxin (90–100% reduction), and (3) antibodies raised against the α-subunit of Gi and Go (55–57% reduction by each), suggesting that A1 receptors interact equally with Gi and Go. (R)-Phenylisopropyladenosine increased the binding of a nonhydrolyzable analogue of GTP to membranes in a pertussis toxin-sensitive manner, indicative of activation of Gi or Go. Previously, (±)-Bay K 8644 enhanced GTP hydrolysis by Go but not Gi. Now we report a profound synergistic stimulation of GTPase in the presence of (R)-phenylisopropyladenosine and (±)-Bay K 8644 (10?7 to 10?5M). (±)-Bay K 8644 had no effect on nucleotide exchange and, thus, cannot activate Go. It appears that a positive cooperative stimulation of Go occurs when it is first activated by A1 receptors and subsequently interacts with the L-type Ca2+ channel. 相似文献
16.
Rosemary S. Hopkins Mark A. Stamnes Melvin I. Simon James B. Hurley 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1988,970(3)
Cholera toxin- and pertussis toxin-catalyzed ADP-ribosylation were used to identify and localize G protein substrates in Drosophila melanogaster and in Manduca sexta. Cholera toxin catalyzes ADP-ribosylation of 37 kDa and 50 kDa polypeptides, but these polypeptides are also substrates for an ADP-ribosyltransferase (EC 2.4.2.30) activity endogenous to the Drosophila extracts. Pertussis toxin modifies 37 kDa and 39 kDa polypeptides in Drosophila homogenates. The pattern of proteolysis of the 39 kDa pertussis toxin substrate is similar to that of mammalian Go and is influenced by guanyl nucleotide binding. The 39 kDa Go-like Drosophila and Manduca pertussis toxin substrates are found primarily in neural tissues. These studies provide further evidence that G proteins are present in Drosophila and that this organism can therefore be used to investigate the physiological roles of these enzymes using advanced genetic manipulations. 相似文献
17.
The sphingosine derivatives sphingosylphosphorylcholine (SPC) and sphingosine-1-phosphate (S1P) caused a similar elevation of the intracellular Ca2+ concentration ([Ca2+]i) in an immortalized airway epithelial cell line (CFNP9o−) incubated in Ca2+-free medium. The maximal effect was obtained with 2 μM SPC and 0.1 μM S1 P and was sensitive to pre-incubation with pertussis toxin, indicating the involvement of a Gi/Go type of G protein. In Ca2+ containing medium, [Ca2+]i elevation by SPC was significantly higher than that by S1P, due to the fact that SPC was able to stimulate Mn2+ entry, whereas S1P was ineffective. SPC, but not S1P, caused a dose-dependent production of total inositol phosphates. Conversely, S1P, but not SPC, increased the level of phosphatidic acid. These findings suggest the presence of two distinct receptors, specific for SPC and S1P, respectively. Depletion of intracellular Ca2+ stores by SPC makes cells unable to respond to a subsequent addition of S1P. Conversely, cells do respond to SPC after a challenge with S1P, suggesting that the two receptors likely share one or more intracellular signalling component(s). 相似文献
18.
《Biochimica et Biophysica Acta (BBA)/General Subjects》1986,884(2):219-224
It has recently been shown in this laboratory that permeabilization of human platelets with 15–25 μm/ml saponin allows ADP-ribosylation by pertussis toxin of the αi-subunit of Gi(Ni), a guanine nucleotide-binding regulatory protein. The same assay conditions have been used to determine phospholipase C in permeabilized platelets. Guanosine 5′-O-thiophosphate- (GTP[γS]-) activated phospholipase C in permeabilized platelets whose inositol phospholipids were prelabeled with [3H]inositol. Phospholipase C activity was measured by [3H]polyphosphoinositide decreases and formation of [3Hinositol bisphosphate and [3H]inositol trisphosphate. Prostacyclin, cyclic AMP or pretreatment of permeabilized platelets with pertussis toxin did not alter this effect under conditions in which the αi-subunit was effectively ADP-ribosylated by pertussis toxin. This information indicated that ADP-ribosylation of Gi-protein was not directly related to activation or inhibition of platelet phospholipase C by GTP[γS]. Thrombin also activated phospholipase C in permeabilized platelets and, surprisingly, this action was enhanced by pertussis toxin pretreatment. This indicated that ADP-ribosylation of Gi-protein facilitates the action of thrombin on phospholipase C. 相似文献
19.
We have demonstrated the ability of peptides derived from the third intracellular loop of GLP-1 receptor to differently modulate
activity of four different types of G-proteins overexpressed in sf9 cells. In this respect, the involvement of Cys341 in inhibition of Gs and Cys341 in activation of Gs and in inhibition of Gi1, Go, and G11, respectively, indicates their potential role in discrimination between different types of G-proteins. Moreover, these two
amino acids from the third intracellular loop might represent an important novel targets for covalent modification by downstream
regulators in signaling through GLP-1 receptor. 相似文献
20.
Extracellular signals are transduced across the cell by the cell surface receptors, with the aid of G-proteins, which act
at a critical point of signal transduction and cellular regulation. Structurally, G-proteins are heterotrimeric consisting
α, β and γ subunits but in functionally active state they dissociate into α subunit coupled to GTP and as βγ dimer. G-proteins
can be broadly divided into two classes based on their sensitivity to pertussis toxin and cholera toxin. Existence of various
forms of each of the subunit allows molecular diversity in the subunit species of G-proteins. These subunits interact with
a wide range of receptors and effectors, facilitated by post translational modification of their subunits. Different types
of G-proteins mediate several signalling events in different parts of the body. This review summarizes the features of (i)
structural and functional heterogenity among different subunits of G-proteins, (ii) interaction of G-proteins and their subunits
with effectors with specific cases of G-protein mediated signalling in olfaction, phototransduction in the retina,
ras andras
related transduction and (iii) disease conditions associated with malfunctioning of G-proteins. 相似文献