Disease relevance of gamma-Thio-GTP

• Activation of a pertussis toxin-sensitive G protein by GTP-gamma-S blocked cGMP-kinase inhibition of the channel [1].
• By contrast, the pretreatment with tetanus and botulinum B neurotoxins did not prevent GTP gamma S-stimulated insulin secretion [2].
• Formation of runoff transcripts including retrovirus RNAs that normally contain 5'-m7GpppGmpC was not decreased by replacing GTP with non-hydrolyzable analogs, and Rous-associated virus-2 runoff products made in the presence of GTP-gamma-S contained 5'-terminal gamma-S-pppGpC [3].
• We now report that G protein activation by GTP gamma S increases the Ba2+ conductance of high-voltage-activated Ca2+ channels of chick dorsal root ganglion (DRG) cells [4].
• Incubation of isolated nuclei with Clostridium botulinum C3 exoenzyme inhibited the potentiating effect of GTP gamma S on ATP-dependent nuclear PLD activity [5].

Psychiatry related information on gamma-Thio-GTP

• GTP gamma S-stimulated adenylyl cyclase activity was significantly lower in Alzheimer's disease superior temporal cortex, but not cerebellum, compared to values from a series of matched control cases [6].

High impact information on gamma-Thio-GTP

• Interestingly, while the earliest steps in stack formation share some similarities with events catalyzing fusion of transport vesicles to its target membrane, neither GTP gamma S nor Rab-GDI, inhibitors of vesicular protein traffic, inhibit stack formation [7].
• In cell lysates, GTP gamma S stimulated PIP 5-kinase activity, and this effect was blocked by botulinum C3 exoenzyme, suggesting that Rho was responsible [8].
• A cytosolic factor markedly enhanced PLD activity in membranes and was essential for GTP gamma S-dependent stimulation of an enriched preparation of PLD [9].
• We now report the complete purification of one component based on its ability to reconstitute GTP gamma S-mediated PLC activity and identify it as the phosphatidylinositol transfer protein (PI-TP) [10].
• The BAPTA-inhibited step in fusion was biochemically distinct from, and occurred later than, the GTP gamma S-sensitive step mediated by the monomeric GTPase, ADP-ribosylation factor [11].

Chemical compound and disease context of gamma-Thio-GTP

• The coupling is mediated by G proteins, since pertussis toxin treatment reduced the K+ current and injection of GTP gamma S (guanosine 5'-O-(thiotriphosphate)) enhanced it [12].
• The activation of phospholipase C in human platelets is coupled to agonist receptors via guanine nucleotide-binding protein(s), and prior treatment of permeabilized platelets with GTP gamma S, GDP beta S, or pertussis toxin modifies platelet responses to agonists [13].
• The absence of a significant rise in inositol 1-monophosphate indicated that phosphatidylinositol hydrolysis was not stimulated by AII or GTP gamma S. Pretreatment of glomerulosa cells with pertussis toxin for 12 h before permeabilization did not inhibit AII- or GTP gamma S-stimulated inositol polyphosphate formation [14].
• Pertussis toxin completely inhibited the ZP-stimulated GTP gamma S binding, but only decreased mastoparan-stimulated GTP gamma S binding by 70-80% [15].
• Overnight pretreatment with pertussis toxin or the addition of guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) or guanosine-5'-O-(2-thiodiphosphate) (GDP-beta-S) instead of GTP to the pipette solution did not alter this current, excluding involvement of G proteins [16].

Biological context of gamma-Thio-GTP

• GTP gamma S irreversibly inhibits protein transport between successive compartments of the Golgi stack in a cell-free system [17].
• Because several vesicular transport steps require GTP hydrolysis, GTP-gamma S may help identify intermediates in synaptic vesicle recycling [18].
• Here we show that GTP is a potent inhibitor of GTP-gamma S-induced degranulation, indicating that sustained activation of a GTP-binding protein is sufficient for membrane fusion [19].
• Presynaptic injection of the nonhydrolyzable GTP analog GTP gamma S irreversibly inhibited neurotransmitter release without changing either the size of the calcium signals produced by presynaptic action potentials or the number of synaptic vesicles docked at presynaptic active zones [20].
• In TCR-modulated CTL, GTP gamma S is no longer able to activate exocytosis [21].

Anatomical context of gamma-Thio-GTP

• Inhibition by GTP gamma S requires a cytosolic inhibitory factor that binds to Golgi membranes during inhibition [17].
• Redistribution of both proteins can be prevented by pretreating cells with AlF4-. Recruitment of adaptors from the cytosol onto the TGN membrane has been reconstituted in a permeabilized cell system and is increased by addition of GTP gamma S and blocked by addition of BFA [22].
• When this coating is exaggerated by GTP gamma S, the periphery of all cisternae is partitioned into coated vesicles that remain attached at their sites of formation [23].
• Intracellular perfusion of mast cells with GTP-gamma S is sufficient to trigger complete exocytotic degranulation in the absence of other intracellular messengers [19].
• We report here that free GTP gamma S-activated G alpha i 1, but not G alpha i 2 or G alpha i 3, potently inhibits G beta 1 gamma 2-induced GIRK activity in excised membrane patches of Xenopus oocytes expressing GIRK1 [24].

Associations of gamma-Thio-GTP with other chemical compounds

• This G protein may be located at a site distinct from the postsynaptic neuron (that is, in presynaptic terminals or glial cells) since maximal activation of CA1 neuronal G proteins by intracellular injection of guanosine-5'-O-(3-thiotriphosphate), a nonhydrolyzable analog of guanosine 5'-triphosphate, did not occlude LTP [25].
• The hydrolysis-resistant GTP analogs, GTP gamma S and GppNHp, were able to stimulate exocytosis at low free Ca2+ concentrations [26].
• However, PAF- and mastoparan-stimulated binding of GTP gamma S to G proteins, which was fully PTX-sensitive, was 2.5-fold higher in HT than NT cell lines [27].
• However, in neurons dialyzed with GTP gamma S, quisqualate and glutamate but not NMDA, kainate, AMPA, or L-APB caused marked and irreversible depressions of the Ca2+ current [28].
• Direct G protein stimulation by GTP gamma S yielded significantly less PA and IP3 in TXA2- platelets [29].

Gene context of gamma-Thio-GTP

• G(o) protein treated with GTP-gamma S lost the ability to associate with APP [30].
• The addition of Sar1p promotes vesicle formation from the ER irrespective of the GTP- or GTP gamma S-bound form, indicating that the active form of Sar1p but not the hydrolysis of GTP is required for this process [31].
• Actin incorporation in the bud can be stimulated by treating the permeabilized cells with GTP-gamma S, and, significantly, the stimulatory effect is eliminated by a mutation in CDC42, a gene that encodes a Rho-like GTP-binding protein required for bud formation [32].
• The vesicles produced are functionally distinct from the ER: they transfer pro-alpha-factor to the Golgi apparatus faster and more efficiently than the ER, they do not require Sec12p or Sec23p to complete transfer, and transfer is resistant to GTP gamma S. Targeting of vesicles to the Golgi apparatus requires Ypt1p and Sec18p [33].
• The weak stimulatory effect of ARF alone suggested that the GTP gamma S-stimulated PLD activity is dependent on the presence of another protein(s), presumably ARF-regulatory proteins [34].

Analytical, diagnostic and therapeutic context of gamma-Thio-GTP

• Electron microscopy demonstrates a corresponding 5-fold accumulation of non-clathrin-coated buds and vesicles associated with the Golgi cisternae during inhibition by GTP gamma S [17].
• In good agreement with these results, microinjection experiments demonstrated that CTX or GTP-gamma-S induced the expression of a PR1-GUS reporter gene but not that of a GLB-GUS reporter gene containing the promoter region of a gene encoding the class I isoform of PR-2 [35].
• Removal of the nucleotide binding protein was also achieved by affinity chromatography with GTP gamma S coupled to Sepharose via a spacer [36].
• Using this effect as the basis of a biological assay, we have isolated a protein from bovine brain cytosol that retards the loss of responsiveness to stimulation by Ca2+ and GTP-gamma-S [37].
• The site of cross-linking between Cys(ACM)Tyr-P gamma-24-45-Cys and alpha t GTP gamma S was localized to within alpha t-306-310 using a variety of chemical and proteolytic cleavages of the cross-linked product, analysis of the fragments with SDS-polyacrylamide gel electrophoresis, and matrix-assisted laser desorption ionization mass spectrometry [38].

References