Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:Q07644 (polypeptide)
 72,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Termination of translation in eukaryotes is governed by two polypeptide chain release factors, eRF1 and eRF3 on the ribosome. eRF1 promotes stop-codon-dependent hydrolysis of peptidyl-tRNA, and eRF3 interacts with eRF1 and stimulates eRF1 activity in the presence of GTP. Here, we have demonstrated that eRF3 is a GTP-binding protein endowed with a negligible, if any, intrinsic GTPase activity that is profoundly stimulated by the joint action of eRF1 and the ribosome. Separately, neither eRF1 nor the ribosome display this effect. Thus, eRF3 functions as a GTPase in the quaternary complex with ribosome, eRF1, and GTP. From the in vitro uncoupling of the peptidyl-tRNA and GTP hydrolyses achieved in this work, we conclude that in ribosomes both hydrolytic reactions are mediated by the formation of the ternary eRF1-eRF3-GTP complex. eRF1 and the ribosome form a composite GTPase-activating protein (GAP) as described for other G proteins. A dual role for the revealed GTPase complex is proposed: in " GTP state," it controls the positioning of eRF1 toward stop codon and peptidyl-tRNA, whereas in "GDP state," it promotes release of eRFs from the ribosome. The initiation, elongation, and termination steps of protein synthesis seem to be similar with respect to GTPase cycles.
 ...
PMID:Eukaryotic polypeptide chain release factor eRF3 is an eRF1- and ribosome-dependent guanosine triphosphatase. 863 14

Septin proteins are necessary for cytokinesis in budding yeast and Drosophila and are thought to be the subunits of the yeast neck filaments. To test whether septins actually form filaments, an immunoaffinity approach was used to isolate a septin complex from Drosophila embryos. The purified complex is comprised of the three previously identified septin polypeptides Pnut, Sep2, and Sep1. Hydrodynamic and sequence data suggest that the complex is composed of a heterotrimer of homodimers. The complex copurifies with one molecule of bound guanine nucleotide per septin polypeptide. It binds and hydrolyzes exogenously added GTP. These observations together with conserved sequence motifs identify the septins as members of the GTPase superfamily. We discuss a model of filament structure and speculate as to how the filaments are organized within cells.
 ...
PMID:A purified Drosophila septin complex forms filaments and exhibits GTPase activity. 863 35

A cDNA encoding the mouse delta opioid receptor was expressed stably in a Rat 1 fibroblast cell line. Expression of this receptor was demonstrated both in ligand binding studies and by reverse transcriptase-PCR. In membranes of clone D2 cells the opioid peptide [D-Ala(2)]-leucine enkephalin (DADLE) produced a robust, concentration-dependent, stimulation of basal high-affinity GTPase activity; the prototypic opioid antagonist naloxone and the highly selective and potent delta opioid ligands H-Tyr-Tic-Phe-Phe-OH (TIPP) and H-Tyr-Tic[Ch2-NH]Phe-Phe-OH (TIPP[psi]) had little effect but N,N-diallyl-Tyr-Aib-Aib-Phe-Leu (ICI174864) caused a marked dose-dependent inhibition of this activity (Tic, 1,2,3,4-tetrahydroisoquinolin-2-yl-carbonyl]; Aib, alpha-aminobutyric acid). This effect of ICI174864 was reversed by TIPP[psi] and attenuated after treatment of the cells with pertussis toxin. No stimulation by DADLE or inhibition by ICI174864 was observed in Rat 1 fibroblasts that did not express the delta opioid receptor. Basal binding of [(35)S]guanosine 5'-O-(3-thio-triphosphate) to membranes of clone D2 cells was also stimulated by DADLE and inhibited by ICI174864; both of these effects were reversed by co-incubation with TIPP[psi]. When cholera toxin-catalysed [(32)P]ADP-ribosylation was performed on membranes of clone D2 cells in the absence of guanine nucleotides, a 40 kDa G1-family polypeptide was labelled in addition to both the long and short isoforms of Gsalpha. Labelling of the 40 kDa polypeptide was enhanced by addition of DADLE and fully attenuated by addition of ICI174864. In contrast, labelling of the isoforms of Gsalpha was unaffected by either opioid ligand. Again, both the positive effect of DADLE and the inhibitory effect of ICI174864 were prevented by co-incubation with TIPP[psi] which, in isolation, had little effect on cholera toxin-catalysed [(32)P]ADP-ribosylation of either Gs or Gi. These data demonstrate that the delta opioid receptor displays a spontaneous activity when expressed in this genetic background. Attenuation of this activity is produced by ICI174864, which by acting as an 'inverse agonist' in this system, functionally uncouples the expressed receptor from the cellular G-protein population. The complete attenuation of agonist-independent cholera toxin-catalysed [(32)P]ADP-ribosylation of Gi demonstrated that ICI174864 acts as an inverse agonist with high intrinsic activity at this receptor.
 ...
PMID:Analysis of inverse agonism at the delta opioid receptor after expression in Rat 1 fibroblasts. 867 Jan 11

Interferon gamma is a pleiotropic cytokine that regulates many immune functions. We have identified a novel protein, inducibly expressed GTPase (IGTP), whose expression was regulated by interferon gamma in macrophages. In mouse RAW 264.7 macrophages, IGTP mRNA levels were almost undetectable but increased within 1 h of exposure to interferon gamma, peaked at very high levels within 3 h, and remained at high levels to at least 48 h; pretreatment of the cells with cycloheximide blocked the majority of mRNA accumulation. In the mouse, the mRNA was highly expressed in thymus, spleen, lung, and small intestine. Using interspecific backcross analysis, the Igtp gene was mapped to mouse chromosome 11. The IGTP cDNA encoded a putative polypeptide of Mr 48,507 and pI 7.79 that contained three consensus GTP binding motifs, GXXXXGK(S/T), DXXG, and NTKXD. Both IGTP that had been immunoprecipitated from RAW cells and a glutathione S-transferase IGTP fusion protein were able to convert GTP to GDP in vitro. Subcellular protein fractionation and Western blotting localized IGTP to the cytosol of RAW cells. In addition, the protein was homologous to proteins encoded by three previously cloned cDNAs, IRG-47, TGTP/Mg21, and LRG-47, and thus may be representative of a new family of interferon gamma-regulated GTPases.
 ...
PMID:Identification of a novel GTPase, the inducibly expressed GTPase, that accumulates in response to interferon gamma. 870 76

G proteins couple receptors for many hormones and neurotransmitters to effectors that regulate second messenger metabolism. G protein-coupled receptors comprise a superfamily with the common structural feature of a single polypeptide with seven membrane-spanning domains. G proteins themselves are heterotrimers with an alpha subunit that binds guanine nucleotides. In the basal state, G proteins tightly bind GDP; receptor activation allows exchange of bound GDP for GTP that activates the G protein and causes it to modulate effector activity. An intrinsic GTPase activity hydrolyzes bound GTP to GDP thereby deactivating the G protein. The effects (cholera, whooping cough) of bacterial toxins that target G proteins for covalent modification signal the potential importance of G protein dysfunction as a cause of human disease. Conceptually, G protein dysfunction could involve gain or loss of function. For Gs, examples of both types have already been defined. Mutations in G protein-coupled receptors have also been identified in several human diseases. Germline loss of function mutations in rhodopsin, cone opsins, the V2 vasopressin receptor, ACTH receptor, and calcium-sensing receptor are responsible for retinitis pigmentosa, color blindness, nephrogenic diabetes insipidus, familial ACTH resistance, and familial hypocalciuric hypercalcemia, respectively. Missense mutations that cause constitutive receptor activation have been identified in the TSH and LH receptors.
 ...
PMID:Defects in G protein-coupled signal transduction in human disease. 881 89

Association reactions of a recombinant CFTR-NBF-2 polypeptide fused to glutathione S-transferase with guanine nucleotides were monitored quantitatively by recording the fluorescence enhancement of excited trinitrophenol (TNP)-labelled GTP after binding to NBF-2. Binding of TNP-GTP to the recombinant NBF-2 polypeptide was characterized by a Kd value of 3.9 microM. The corrected Kd values for unlabelled guanine nucleotides were determined to be 33 microM for GTP, 92 microM for GDP and 217 microM for GMP. TNP-ATP bound to NBF-2 was competitively displaced by GTP indicating a common binding site for both nucleotides. The recombinant NBF-2 did not show an intrinsic GTPase activity above a detection limit of 0.007 min(-1). Our findings provide the first experimental evidence that NBF-2 can act as a GTP-binding subunit that would favor the release of GDP after GTP hydrolysis.
 ...
PMID:A recombinant polypeptide model of the second predicted nucleotide binding fold of the cystic fibrosis transmembrane conductance regulator is a GTP-binding protein. 894 60

The Rho family of small GTP-binding proteins plays important roles in the regulation of actin cytoskeleton organization and cell growth. Activation of these GTPases involves the replacement of bound GDP with GTP, a process catalyzed by the Dbl-like guanine-nucleotide exchange factors, all of which seem to share a putative catalytic motif termed the Dbl homology (DH) domain, followed by a pleckstrin homology (PH) domain. Here we have examined the role of a Dbl-like molecule, the faciogenital dysplasia gene product (FGD1), which when mutated in its Dbl homology domain, cosegregates with the developmental disease Aarskog-Scott syndrome. We report that a polypeptide of FGD1 encompassing the DH and PH domains can bind specifically to the Rho family GTPase Cdc42Hs and stimulates the GDP-GTP exchange of the isoprenylated form of Cdc42Hs. Microinjection of this FGD1 polypeptide into Swiss 3T3 fibroblast cells induces the formation of peripheral actin microspikes, similar to that previously observed when cells were injected with a constitutively active form of Cdc42Hs. This effect of FGD1 on actin organization is readily inhibited by coinjection of a dominant-negative mutant of Cdc42Hs. Examination of NIH 3T3 cells expressing the FGD1 fragment revealed that similar to cells expressing Dbl, two independent elements downstream of Cdc42Hs, the Jun NH2-terminal kinase and the p70 S6 kinase, became activated. Hence, our results indicate that FGD1, through its DH and PH domains, acts as a Cdc42Hs-specific guanine-nucleotide exchange factor and suggest that the Cdc42Hs GTPase may have a role in mammalian development.
 ...
PMID:The faciogenital dysplasia gene product FGD1 functions as a Cdc42Hs-specific guanine-nucleotide exchange factor. 896 70

Elongation factor Tu (EF-Tu) from Escherichia coli carrying the mutation G222D is unable to hydrolyze GTP on the ribosome and to sustain polypeptide synthesis at near physiological Mg2+ concentration, although the interactions with guanine nucleotides and aminoacyl-tRNA are not changed significantly. GTPase and polypeptide synthesis activities are restored by increasing the Mg2+ concentration. Here we report a pre-steady-state kinetic study of the binding of the ternary complexes of wild-type and mutant EF-Tu with Phe-tRNA(Phe) and GTP to the A site of poly(U)-programed ribosomes. The kinetic parameters of initial binding to the ribosome and subsequent codon-anticodon interaction are similar for mutant and wild-type EF-Tu, independent of the Mg2+ concentration, suggesting that the initial interaction with the ribosome is not affected by the mutation. Codon recognition following initial binding is also not affected by the mutation. The main effect of the G222D mutation is the inhibition, at low Mg2+ concentration, of codon-induced structural transitions of the tRNA and, in particular, their transmission to EF-Tu that precedes GTP hydrolysis and the subsequent steps of A-site binding. Increasing the Mg2+ concentration to 10 mM restores the complete reaction sequence of A-site binding at close to wild-type rates. The inhibition of the structural transitions is probably due to the interference of the negative charge introduced by the mutation with negative charges either of the 3' terminus of the tRNA, bound in the vicinity of the mutated amino acid in domain 2 of EF-Tu, or of the ribosome. Increasing the Mg2+ concentration appears to overcome the inhibition by screening the negative charges.
 ...
PMID:The G222D mutation in elongation factor Tu inhibits the codon-induced conformational changes leading to GTPase activation on the ribosome. 897 2

The tuberous sclerosis-2 (TSC2) gene is linked to tuberous sclerosis (TSC), a dominantly inherited genetic syndrome in which inactivation of the normal TSC2 allele is associated with the development of mostly benign tumors and focal dysplasias. TSC2 encodes the protein tuberin, which is a widely expressed 180-kd polypeptide that exhibits specific GTPase activating activity toward Rap1 in vitro and co-localizes with Rap1 in cultured cells. In this study, we have performed immunohistochemical analyses, using affinity-purified anti-tuberin antibodies, to study the distribution of tuberin in a panel of normal human organs that are commonly affected by TSC. Cryosections indicated that tuberin is widely expressed at low levels. More intense staining of tuberin, in the cryosections and in paraffin sections, was observed in the small blood vessels of many organs, including the kidney, skin, and adrenal gland. High levels of tuberin were also detected in cortical neurons and cerebellar Purkinje cells. These findings imply that loss-of-function mutations in TSC2 might lead to the development of highly vascularized tumors, subcortical tubers, and focal atrophy of the cerebellar cortex, which are features commonly associated with TSC. Moreover, Rap1 was also found to be highly expressed in many of the same cells that contained high levels of tuberin, suggesting a functional interaction between tuberin and Rap1 in these tissues.
 ...
PMID:Expression of the TSC2 product tuberin and its target Rap1 in normal human tissues. 900 20

The expression of genes transcribed by the RNA polymerase with the alternative sigma factor sigma 54 (E sigma 54) is absolutely dependent on activator proteins that bind to enhancer-like sites, located far upstream from the promoter. These unique prokaryotic proteins, known as enhancer-binding proteins (EBP), mediate open promoter complex formation in a reaction dependent on NTP hydrolysis. The best characterized proteins of this family of regulators are NtrC and NifA, which activate genes required for ammonia assimilation and nitrogen fixation, respectively. In a recent IRBM course (@ontiers of protein structure prediction," IRBM, Pomezia, Italy, 1995; see web site http://www.mrc-cpe.cam.uk/irbm-course95/), one of us (J.O.) participated in the elaboration of the proposal that the Central domain of the EBPs might adopt the classical mononucleotide-binding fold. This suggestion was based on the results of a new protein fold recognition algorithm (Map) and in the mapping of correlated mutations calculated for the sequence family on the same mononucleotide-binding fold topology. In this work, we present new data that support the previous conclusion. The results from a number of different secondary structure prediction programs suggest that the Central domain could adopt an alpha/beta topology. The fold recognition programs ProFIT 0.9, 3D PROFILE combined with secondary structure prediction, and 123D suggest a mononucleotide-binding fold topology for the Central domain amino acid sequence. Finally, and most importantly, three of five reported residue alterations that impair the Central domain. ATPase activity of the E sigma 54 activators are mapped to polypeptide regions that might be playing equivalent roles as those involved in nucleotide-binding in the mononucleotide-binding proteins. Furthermore, the known residue substitution that alter the function of the E sigma 54 activators, leaving intact the Central domain ATPase activity, are mapped on region proposed to play an equivalent role as the effector region of the GTPase superfamily.
 ...
PMID:A proposed architecture for the central domain of the bacterial enhancer-binding proteins based on secondary structure prediction and fold recognition. 907 Apr 37


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>