701
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Identification of residues of the H-ras protein critical for functional interaction with guanine nucleotide exchange factors. Mol Cell Biol 1994. [PMID: 8289791 DOI: 10.1128/mcb.14.2.1104] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ras proteins are activated in vivo by guanine nucleotide exchange factors encoded by genes homologous to the CDC25 gene of Saccharomyces cerevisiae. We have taken a combined genetic and biochemical approach to probe the sites on Ras proteins important for interaction with such exchange factors and to further probe the mechanism of CDC25-catalyzed GDP-GTP exchange. Random mutagenesis coupled with genetic selection in S. cerevisiae was used to generate second-site mutations within human H-ras-ala15 which could suppress the ability of the Ala-15 substitution to block CDC25 function. We transferred these second-site suppressor mutations to normal H-ras and oncogenic H-rasVal-12 to test whether they induced a general loss of function or whether they selectively affected CDC25 interaction. Four highly selective mutations were discovered, and they affected the surface-located amino acid residues 62, 63, 67, and 69. Two lines of evidence suggested that these residues may be involved in binding to CDC25: (i) using the yeast two-hybrid system, we demonstrated that these mutants cannot bind CDC25 under conditions where the wild-type H-Ras protein can; (ii) we demonstrated that the binding to H-Ras of monoclonal antibody Y13-259, whose epitope has been mapped to residues 63, 65, 66, 67, 70, and 73, is blocked by the mouse sos1 and yeast CDC25 gene products. We also present evidence that the mechanism by which CDC25 catalyzes exchange is more involved than simply catalyzing the release of bound nucleotide and passively allowing nucleotides to rebind. Most critically, a complex of Ras and CDC25 protein, unlike free Fas protein, possesses significantly greater affinity for GTP than for GDP. Furthermore, the Ras CDC25 complex is more readily dissociated into free subunits by GTP than it is by GDP. Both of these results suggest a function for CDC25 in promoting the selective exchange of GTP for GDP.
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702
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Stenmark H, Valencia A, Martinez O, Ullrich O, Goud B, Zerial M. Distinct structural elements of rab5 define its functional specificity. EMBO J 1994; 13:575-83. [PMID: 8313902 PMCID: PMC394846 DOI: 10.1002/j.1460-2075.1994.tb06295.x] [Citation(s) in RCA: 123] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Members of the rab family of small GTPases are localized to distinct cellular compartments and function as specific regulators of vesicle transport between organelles. Overexpression of rab5, which is associated with early endosomes and the plasma membrane, increases the rate of endocytosis [Bucci et al. (1992) Cell, 70, 715-728]. From sequence alignments and molecular modelling we identified structural elements that might contribute to the definition of the functional specificity of rab5. To test the role of these elements experimentally, we transplanted them onto rab6, which is associated with the Golgi complex. The chimeric proteins were assayed for intracellular localization and stimulation of endocytosis. First, we found that the C-terminus of rab5 could target rab6 to the plasma membrane and early endosomes but it did not confer rab5-like stimulation of endocytosis. Further replacement of other regions revealed that the N-terminus, helix alpha 2/loop 5 and helix alpha 2/loop 7 were all required to functionally convert rab6 into rab5. Reciprocal hybrids of rab5 containing these regions replaced with those of rab6 were inactive, demonstrating that each region is essential for rab5 function. These results indicate that distinct structural elements specify the localization, membrane association and regulatory function of rab5.
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Affiliation(s)
- H Stenmark
- European Molecular Biology Laboratory, D-6900 Heidelberg, Germany
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703
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Mosteller RD, Han J, Broek D. Identification of residues of the H-ras protein critical for functional interaction with guanine nucleotide exchange factors. Mol Cell Biol 1994; 14:1104-12. [PMID: 8289791 PMCID: PMC358466 DOI: 10.1128/mcb.14.2.1104-1112.1994] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Ras proteins are activated in vivo by guanine nucleotide exchange factors encoded by genes homologous to the CDC25 gene of Saccharomyces cerevisiae. We have taken a combined genetic and biochemical approach to probe the sites on Ras proteins important for interaction with such exchange factors and to further probe the mechanism of CDC25-catalyzed GDP-GTP exchange. Random mutagenesis coupled with genetic selection in S. cerevisiae was used to generate second-site mutations within human H-ras-ala15 which could suppress the ability of the Ala-15 substitution to block CDC25 function. We transferred these second-site suppressor mutations to normal H-ras and oncogenic H-rasVal-12 to test whether they induced a general loss of function or whether they selectively affected CDC25 interaction. Four highly selective mutations were discovered, and they affected the surface-located amino acid residues 62, 63, 67, and 69. Two lines of evidence suggested that these residues may be involved in binding to CDC25: (i) using the yeast two-hybrid system, we demonstrated that these mutants cannot bind CDC25 under conditions where the wild-type H-Ras protein can; (ii) we demonstrated that the binding to H-Ras of monoclonal antibody Y13-259, whose epitope has been mapped to residues 63, 65, 66, 67, 70, and 73, is blocked by the mouse sos1 and yeast CDC25 gene products. We also present evidence that the mechanism by which CDC25 catalyzes exchange is more involved than simply catalyzing the release of bound nucleotide and passively allowing nucleotides to rebind. Most critically, a complex of Ras and CDC25 protein, unlike free Fas protein, possesses significantly greater affinity for GTP than for GDP. Furthermore, the Ras CDC25 complex is more readily dissociated into free subunits by GTP than it is by GDP. Both of these results suggest a function for CDC25 in promoting the selective exchange of GTP for GDP.
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Affiliation(s)
- R D Mosteller
- Department of Biochemistry and Molecular Biology, Kenneth Norris Jr. Cancer Hospital and Research Center, University of Southern California School of Medicine, Los Angeles 90033
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704
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Affiliation(s)
- A Wittinghofer
- Max-Planck-Institut für Molekulare Physiologie, Abteilung Strukturelle Biologie, Dortmund, Federal Republic of Germany
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705
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Yamasaki K, Shirouzu M, Muto Y, Fujita-Yoshigaki J, Koide H, Ito Y, Kawai G, Hattori S, Yokoyama S, Nishimura S. Site-directed mutagenesis, fluorescence, and two-dimensional NMR studies on microenvironments of effector region aromatic residues of human c-Ha-Ras protein. Biochemistry 1994; 33:65-73. [PMID: 8286364 DOI: 10.1021/bi00167a009] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The Tyr residues in positions 32 and 40 of human c-Ha-Ras protein were replaced by site-directed mutagenesis (Y32F, Y32W, Y40K, and Y40W) to examine their roles in the signal-transducing activity and the sensitivity to the GTPase activating protein (GAP). The signal-transducing activity of the oncogenic Ras protein in PC12 cells was lost upon mutations Y32F and Y40K, but retained upon mutations Y32W and Y40W. These results suggest that residues 32 and 40 are both required to have aromatic groups and residue 32 is further required to have a hydrogen donor. On the other hand, three mutations (Y32F, Y32W, and Y40W) caused no appreciable reduction in either GAP-binding affinity or GAP sensitivity. By the Y40K mutation, GAP-binding affinity was slightly lowered, while GAP sensitivity was drastically impaired. Therefore, for residues 32 and 40 of Ras, interactions with GAP appear to be different from those with the target of signal transduction in the PC12 cell. As for the Y32W-Ras protein bound with an unhydrolyzable GTP analogue (GMPPNP), the Trp32 fluorescence is appreciably red-shifted, weaker, and more susceptible to KI quenching as compared to that of the GDP-bound form. Two-dimensional NMR spectroscopy with selectively deuterated Ras proteins revealed fewer and weaker nuclear Overhauser effects on the aromatic protons of Trp32 in the GMPPNP-bound form than in the GDP-bound form. This indicates that the side chain of Trp32 is more exposed to the solvent in the GMPPNP-bound form than in the GDP-bound form.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- K Yamasaki
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Japan
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706
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Ramaschi G, Balduini C, Torti M, Sinigaglia F. Effect of cAMP on the association of small GTP-binding proteins with the cytoskeleton of human platelets. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1199:20-6. [PMID: 8280749 DOI: 10.1016/0304-4165(94)90091-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Following activation of human platelets changes in cytoskeletal organization occur: some proteins, which are present in the cytosol or membrane-associated in resting platelets, are recovered in the Triton-insoluble residue in activated cells. Assembly and disassembly of complex effector units on the membrane and inside cells is under the control of low molecular weight GTP-binding proteins, particularly those in the ras family. We investigated the interaction of small GTP-binding proteins with the platelet cytoskeleton and the effect of high cAMP levels on these interactions. At least two GTP-binding proteins of 24 and 28 kDa were detected in the Triton-insoluble residue of resting platelets. Stimulation of platelets with thrombin or concanavalin A (Con A), under non-aggregating conditions, resulted in increased 24 kDa protein-bound GTP, which also contained a significant amount of rap1B. High cAMP levels differently affected this interaction depending on the type of agonist used. cAMP increased association of G-proteins with the cytoskeleton following Con A-activation, while it decreased G-proteins interaction after thrombin stimulation. The activation did not influence the cAMP-dependent phosphorylation of rap1B. No phosphoprotein corresponding to rap1B could be detected in the Triton-insoluble residues, however. These findings could be related to the different mechanisms of cytoskeletal protein recruitment in platelets activated with either thrombin or Con A.
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Affiliation(s)
- G Ramaschi
- Department of Biochemistry, University of Pavia, Italy
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707
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Abstract
Heterotrimeric GTP-binding proteins (G proteins) that are made up of alpha and beta gamma subunits couple many kinds of cell-surface receptors to intracellular effector enzymes or ion channels. Every cell contains several types of receptors, G proteins, and effectors. The specificity with which G protein subunits interact with receptors and effectors defines the range of responses a cell is able to make to an external signal. Thus, the G proteins act as a critical control point that determines whether a signal spreads through several pathways or is focused to a single pathway. In this review, I will summarize some features of the structure and function of mammalian G protein subunits, discuss the role of both alpha and beta gamma subunits in regulation of effectors, the role of the beta gamma subunit in macromolecular assembly, and the mechanisms that might make some responses extremely specific and others rather diffuse.
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Affiliation(s)
- E J Neer
- Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115
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708
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Lorenz J, Friedberg T, Paulus R, Oesch F, Ferlinz R. Oncogene overexpression in non-small-cell lung cancer tissue: prevalence and clinicopathological significance. THE CLINICAL INVESTIGATOR 1994; 72:156-63. [PMID: 8186664 DOI: 10.1007/bf00184595] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In contrast to small-cell lung cancer, few data are available on the role of oncogene overexpression in non-small-cell lung cancers (NSCLC). To determine the prevalence and extent of the transcriptional activation of cancer genes in NSCLC we investigated the level of mRNA of the three important cellular oncogenes--erbB2, Ki-ras, and c-myc--in 39 surgically or endoscopically obtained tumor samples and 24 samples of normal bronchopulmonary tissue taken from the same patients. Tissue RNA was prepared and the specific mRNA analyzed by the highly sensitive nuclease S1 protection assay. Oncogene mRNA in the tumors was quantified by comparison with the homogeneously weak signals in normal lung tissue preparations with densitometry. The presence of two- to four-fold excess RNA was defined as moderate and a greater than fourfold RNA amount as strong gene overexpression. In contrast to normal tissue the oncogene mRNA amount varied considerably among tumors, showing increases up to 64-fold in erbB2, 13-fold in Ki-ras, and 57-fold in c-myc. Moderate and strong (in brackets) mRNA overexpression occurred with 33% (33%) in erbB2, 36% (18%) in Ki-ras, and 18% (23%) in c-myc. Simultaneous overexpression of two genes was observed with 41% and increased mRNA of all genes tested with 20% of the NSCLC samples. Augmented oncogene mRNA was observed most frequently in large-cell carcinoma. The c-myc overexpression was significantly more prevalent in large-cell cancer than in adenocarcinoma. Tumor differentiation was negatively correlated with c-myc mRNA amounts.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J Lorenz
- III. Medizinische Klinik und Poliklinik, Johannes Gutenberg Universität, Mainz
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709
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710
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Markby DW, Onrust R, Bourne HR. Separate GTP binding and GTPase activating domains of a G alpha subunit. Science 1993; 262:1895-901. [PMID: 8266082 DOI: 10.1126/science.8266082] [Citation(s) in RCA: 135] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Most members of the guanosine triphosphatase (GTPase) superfamily hydrolyze guanosine triphosphate (GTP) quite slowly unless stimulated by a GTPase activating protein or GAP. The alpha subunits (G alpha) of the heterotrimeric G proteins hydrolyze GTP much more rapidly and contain an approximately 120-residue insert not found in other GTPases. Interactions between a G alpha insert domain and a G alpha GTP-binding core domain, both expressed as recombinant proteins, show that the insert acts biochemically as a GAP. The results suggest a general mechanism for GAP-dependent hydrolysis of GTP by other GTPases.
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Affiliation(s)
- D W Markby
- Department of Pharmcology, University of California, San Francisco 94143
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711
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Noel JP, Hamm HE, Sigler PB. The 2.2 A crystal structure of transducin-alpha complexed with GTP gamma S. Nature 1993; 366:654-63. [PMID: 8259210 DOI: 10.1038/366654a0] [Citation(s) in RCA: 643] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The 2.2 A crystal structure of activated rod transducin, Gt alpha.GTP gamma S, shows the bound GTP gamma S molecule occluded deep in a cleft between a domain structurally homologous to small GTPases and a helical domain unique to heterotrimeric G proteins. The structure, when combined with biochemical and genetic studies, suggests: how an activated receptor might open this cleft to allow nucleotide exchange; a mechanism for GTP-induced changes in effector and receptor binding surfaces; and a mechanism for GTPase activity not evident from previous data.
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Affiliation(s)
- J P Noel
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06510
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712
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First EA, Fersht AR. Involvement of threonine 234 in catalysis of tyrosyl adenylate formation by tyrosyl-tRNA synthetase. Biochemistry 1993; 32:13644-50. [PMID: 8257697 DOI: 10.1021/bi00212a032] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
There is a mobile loop in the tyrosyl-tRNA synthetase that contains the KMSKS signature sequence of class I aminoacyl-tRNA synthetases. As it has not been possible to determine the role of the mobile loop in catalysis from X-ray crystallographic studies, we are investigating its importance by a series of site-directed mutagenic and kinetic studies. Here we examine the role of threonine 234 (T234) in the catalysis of tyrosyl adenylate formation by tyrosyl-tRNA synthetase from Bacillus stearothermophilus. This residue is the carboxy-terminal residue in the signature sequence and is either a serine or threonine in eight of the ten class I aminoacyl-tRNA synthetases isolated from Escherichia coli. Kinetic analyses of tyrosyl adenylate formation in the mutant enzymes indicate that k3, the forward rate constant for the formation of tyrosyl adenylate, is reduced 500-fold on mutation of T234 to alanine. In contrast, mutation of T234 to serine results in only a 4-fold decrease in k3, suggesting that the loss of the hydroxyl group in the T234A mutant is responsible for its decreased reaction rate. Deletion of the hydroxyl group destabilizes the transition state for the formation of tyrosyl adenylate by 2.7 kcal/mol. The transition state is also destabilized by 1.4 kcal/mol on the mutation of K230 to alanine. The effects of mutation of both T234 and K230 to alanine are less than additive; there is a coupling energy of -1.3 kcal/mol in the transition state. The effects of mutating K230 and T234 to alanine are also nonadditive in the E.Tyr-AMP complex (coupling energy = -1.9 kcal/mol).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- E A First
- MRC Unit for Protein Function and Design, University Chemical Laboratory, Cambridge, U.K
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713
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Hazlett TL, Moore KJ, Lowe PN, Jameson DM, Eccleston JF. Solution dynamics of p21ras proteins bound with fluorescent nucleotides: a time-resolved fluorescence study. Biochemistry 1993; 32:13575-83. [PMID: 8257693 DOI: 10.1021/bi00212a025] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The solution dynamics of normal and transforming p21ras proteins in both the GTP- and GDP-bound forms were examined with time-resolved fluorescence spectroscopy. The fluorescent 2'(3')-O-(N-methylanthraniloyl) derivatives (mant derivatives) of GTP, dGTP, and GDP and the aminocoumarin and fluorescein derivatives of GTP and GDP were synthesized and used as reporter groups. The fluorescence lifetimes at 5 degrees C of the mant nucleotide derivatives increased from approximately 4 ns in solution to approximately 9 ns when bound to p21ras. At 30 degrees C, there was a 7.8% difference in lifetime between normal p21ras.mantGTP and p21ras.mantGDP, but no difference between similar complexes of the [Asp-12]p21ras protein. These data are consistent with steady-state fluorescence intensity differences among p21ras.mantGTP, p21ras.mantGDP, and the free nucleotides. Rotational correlation times for the mantGTP- and mantGDP-bound p21 proteins, N-ras, K-ras, and H-ras, were similar at 26 ns (5 degrees C), which is significantly longer than the 15-ns rotational correlation time predicted for a globular 21,000-Da protein. The p21-bound fluorescein and aminocoumarin nucleotide derivatives reported correlation times of 19 and 29 ns, respectively. Global analysis of the three fluorophore.p21 complexes with linked protein rotational correlation functions were best fit with a common rotational correlation time of 28 ns. Gel permeation chromatography of the GDP and mantGDP complexes of normal p21N-ras also showed greater apparent molecular weights than were expected in both cases, demonstrating that the high rotational correlation times obtained from time-resolved fluorescence measurements were not a result of the introduction of the fluorophore.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- T L Hazlett
- Department of Physics, University of Illinois at Urbana, Champaign 61801
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714
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Affiliation(s)
- A Wittinghofer
- Max-Planck-Institut für molekulare Physiologie, Postfach 10 26 64, 44026 Dortmund, Germany
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715
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Kumar KA, Mahalakshmi S, Muniyappa K. DNA-induced conformational changes in RecA protein. Evidence for structural heterogeneity among nucleoprotein filaments and implications for homologous pairing. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)74295-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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716
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Connolly T, Gilmore R. GTP hydrolysis by complexes of the signal recognition particle and the signal recognition particle receptor. J Cell Biol 1993; 123:799-807. [PMID: 8227141 PMCID: PMC2200155 DOI: 10.1083/jcb.123.4.799] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Translocation of proteins across the endoplasmic reticulum membrane is a GTP-dependent process. The signal recognition particle (SRP) and the SRP receptor both contain subunits with GTP binding domains. One GTP-dependent reaction during protein translocation is the SRP receptor-mediated dissociation of SRP from the signal sequence of a nascent polypeptide. Here, we have assayed the SRP and the SRP receptor for GTP binding and hydrolysis activities. GTP hydrolysis by SRP was not detected, so the maximal GTP hydrolysis rate for SRP was estimated to be < 0.002 mol GTP hydrolyzed x mol of SRP-1 x min-1. The intrinsic GTP hydrolysis activity of the SRP receptor ranged between 0.02 and 0.04 mol GTP hydrolyzed x mol of SRP receptor-1 x min-1. A 40-fold enhancement of GTP hydrolysis activity relative to that observed for the SRP receptor alone was obtained when complexes were formed between SRP and the SRP receptor. GTP hydrolysis activity was inhibited by GDP, but not by ATP. Extended incubation of the SRP or the SRP receptor with GTP resulted in substoichiometric quantities of protein-bound ribonucleotide. SRP-SRP receptor complexes engaged in GTP hydrolysis were found to contain a minimum of one bound guanine ribonucleotide per SRP-SRP receptor complex. We conclude that the GTP hydrolysis activity described here is indicative of one of the GTPase cycles that occur during protein translocation across the endoplasmic reticulum.
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Affiliation(s)
- T Connolly
- Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester 01655
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717
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Chung HH, Benson DR, Cornish VW, Schultz PG. Probing the role of loop 2 in Ras function with unnatural amino acids. Proc Natl Acad Sci U S A 1993; 90:10145-9. [PMID: 8234268 PMCID: PMC47730 DOI: 10.1073/pnas.90.21.10145] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The YDPT sequence motif (residues 32-35) in loop 2 (residues 32-40) of Ha-Ras p21 protein is conserved in the Ras protein family. X-ray crystal structures have revealed significant conformational differences in this region between the GTP- and GDP-bound forms. Moreover, mutations in this region block neoplastic transformation and prevent interaction with GTPase-activating protein (GAP), suggesting that this region may contribute to the effector function of Ras. To better understand the structural features required for GAP interaction and GTPase activity, the expanded repertoire of unnatural amino acid mutagenesis has been used to investigate the roles of the key residues, Pro-34, Thr-35, and Ile-36. A Pro-34-->methanoproline mutant, in which residue 34 is locked in the trans conformation, was found to retain high levels of intrinsic and GAP-activated GTPase activity, making unlikely conformational isomerization at this position. Deletion of a single methyl group from Ile (Ile-36-->norvaline) abolished GAP activation of Ras, revealing a remarkable specificity in this protein-protein interaction. Finally, replacement of Thr-35 with diastereomeric allo-threonine led to inactivation of Ras, demonstrating the importance of the orientation of this critical residue in Ras function.
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Affiliation(s)
- H H Chung
- Department of Chemistry, University of California, Lawrence Berkeley Laboratory, Berkeley 94720-9989
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718
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Thomas TC, Schmidt CJ, Neer EJ. G-protein alpha o subunit: mutation of conserved cysteines identifies a subunit contact surface and alters GDP affinity. Proc Natl Acad Sci U S A 1993; 90:10295-9. [PMID: 8234290 PMCID: PMC47761 DOI: 10.1073/pnas.90.21.10295] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The reversible association of alpha and beta gamma subunits of GTP-binding proteins is important for signal transmission from a variety of cell-surface receptors to intracellular effectors. Previous work showed that 1,6-bis(maleimido)hexane, which crosslinks cysteine residues, crosslinks alpha o and alpha i-1 to beta gamma. These crosslinks are likely to form through a conserved cysteine because 1,6-bis(maleimido)hexane can also crosslink alpha i-2, alpha 1, alpha s and Drosophila alpha 1 to give products of the same apparent molecular weight as crosslinked alpha o beta gamma and alpha i-1 beta gamma. These proteins have only two cysteines in common. Therefore, we mutated each of the two conserved cysteines of alpha o to alanines. Mutation of Cys215 prevents crosslinking to beta gamma, but does not affect binding of guanosine 5'-[gamma-thio]triphosphate or the ability of the mutated alpha subunit to bind beta gamma. In models of the alpha subunit based on the crystal structure of p21ras, Cys215 is located on the face opposite to the GTP-binding site and near an area that changes conformation depending on the nucleotide bound. This surface on the alpha subunit overlaps a putative effector binding region, raising important questions about the spatial organization of the proteins as they form ternary complexes. Mutation of Cys325 has no effect on crosslinking but, surprisingly, decreases by a factor of 10 the affinity of the mutated protein for GDP, relative to wild type, without changing the affinity for guanosine 5'-[gamma-thio]triphosphate. This mutation falls within a region thought to contact receptors and may represent a site through which receptors enhance the release of GDP.
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Affiliation(s)
- T C Thomas
- Department of Medicine, Brigham and Women's Hospital, Boston, MA
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719
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McKiernan C, Brondyk W, Macara I. The Rab3A GTPase interacts with multiple factors through the same effector domain. Mutational analysis of cross-linking of Rab3A to a putative target protein. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(20)80546-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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720
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Aggeler R, Cai S, Keana J, Koike T, Capaldi R. The gamma subunit of the Escherichia coli F1-ATPase can be cross-linked near the glycine-rich loop region of a beta subunit when ADP + Mg2+ occupies catalytic sites but not when ATP + Mg2+ is bound. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)36860-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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721
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Weijland A, Sarfati R, Bârzu O, Parmeggiani A. Asparagine-135 of elongation factor Tu is a crucial residue for the folding of the guanine nucleotide binding pocket. FEBS Lett 1993; 330:334-8. [PMID: 8375504 DOI: 10.1016/0014-5793(93)80899-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
This work studies the structure-function relationships of Asn135, a residue situated in the GTP binding pocket of elongation factor Tu (EF-Tu). For this purpose we constructed EF-TuN135D/D138N and assayed its reactivity towards various purine nucleotides. We found that EF-TuN135D/D138N had no functional effect with GTP, ATP, XTP and isoGTP. The lack of a productive interaction with isoGTP shows that the Asn135 side-chain does not recognize the exocyclic keto group of the guanine base. However, EF-TuN135D/D138N, whose native conformation is stabilized by either elongation factor Ts or kirromycin, was able to support the enzymatic binding of aa-tRNA to the ribosome in the absence of any nucleotide, when in complex with the antibiotic. Taken together, these results show that Asn135 is important for the correct folding of the nucleotide binding site and that EF-Tu.kirromycin can mediate the binding of aa-tRNA to the mRNA-programmed ribosomes independently of the native conformation of this site.
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Affiliation(s)
- A Weijland
- SDI n. 61840 du CNRS, Laboratoire de Biochimie, Ecole Polytechnique, Palaiseau, France
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722
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Koide H, Satoh T, Nakafuku M, Kaziro Y. GTP-dependent association of Raf-1 with Ha-Ras: identification of Raf as a target downstream of Ras in mammalian cells. Proc Natl Acad Sci U S A 1993; 90:8683-6. [PMID: 8378348 PMCID: PMC47422 DOI: 10.1073/pnas.90.18.8683] [Citation(s) in RCA: 141] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Ras is involved in signal transduction of various factors for growth, differentiation, and oncogenesis. Recent studies have revealed several proteins that function upstream and downstream of the Ras signaling pathway. However, its immediate downstream target molecular has not yet been identified. In an effort to identify the Ras-associated downstream proteins, we added recombinant Ha-Ras in a GTP-bound form to cell-free lysates and used several antibodies against Ras to immunoprecipitate Ras complexes. We found that a serine/threonine kinase, Raf-1, was coimmunoprecipitated with Ha-Ras by two anti-Ras antibodies (LA069 and Y13-238), whereas a neutralizing antibody against Ras (Y13-259) could not precipitate Raf-1. The coimmunoprecipitation was observed with a complex of Ras and guanosine 5'-[gamma- thio]triphosphate but not with a complex of Ras and guanosine 5'-[beta-thio]diphosphate. The GTP-dependent association of Ha-Ras with Raf-1 was observed with lysates of various types of cultured cells, including NIH 3T3, pheochromocytoma (PC) 12, Ba/F3, and Jurkat T cells, and also with crude extracts from rat brain. Furthermore, Raf-1 was precipitated with a transforming Ha-Ras mutant ([Val12]Ras) and wild-type Ha-Ras but not with an effector-region mutant ([Leu35,ARg37]Ras) that lacks transforming activity. These results indicate that Ras.GTP physically associates with Raf either directly or through other component(s) and strongly suggest that Raf functions in close downstream proximity to Ras in mammalian cells.
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Affiliation(s)
- H Koide
- DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, CA 94304-1104
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723
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Kjeldgaard M, Nissen P, Thirup S, Nyborg J. The crystal structure of elongation factor EF-Tu from Thermus aquaticus in the GTP conformation. Structure 1993; 1:35-50. [PMID: 8069622 DOI: 10.1016/0969-2126(93)90007-4] [Citation(s) in RCA: 316] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND Elongation factor Tu (EF-Tu) is a GTP-binding protein that is crucial for protein biosynthesis. In the GTP form of the molecule, EF-Tu binds tightly to aminoacyl-tRNA, forming a ternary complex that interacts with the ribosomal acceptor site. During this interaction, GTP is hydrolyzed, and EF-Tu.GDP is ejected. RESULTS The crystal structure of EF-Tu from Thermus aquaticus, complexed to the GTP analogue GDPNP, has been determined at 2.5 A resolution and compared to the structure of Escherichia coli EF-Tu.GDP. During the transition from the GDP (inactive) to the GTP (active) form, domain 1, containing the GTP-binding site, undergoes internal conformational changes similar to those observed in ras-p21. In addition, a dramatic rearrangement of domains is observed, corresponding to a rotation of 90.8 degrees of domain 1 relative to domains 2 and 3. Residues that are affected in the binding of aminoacyl-tRNA are found in or near the cleft formed by the domain interface. CONCLUSION GTP binding by EF-Tu leads to dramatic conformational changes which expose the tRNA binding site. It appears that tRNA binding to EF-Tu induces a further conformational change, which may affect the GTPase activity.
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Affiliation(s)
- M Kjeldgaard
- Department of Chemistry, Aarhus University, Denmark
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724
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Berchtold H, Reshetnikova L, Reiser CO, Schirmer NK, Sprinzl M, Hilgenfeld R. Crystal structure of active elongation factor Tu reveals major domain rearrangements. Nature 1993; 365:126-32. [PMID: 8371755 DOI: 10.1038/365126a0] [Citation(s) in RCA: 419] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The crystal structure of intact elongation factor Tu (EF-Tu) from Thermus thermophilus has been determined and refined at an effective resolution of 1.7 A, with incorporation of data extending to 1.45 A. The effector region, including interaction sites for the ribosome and for transfer RNA, is well defined. Molecular mechanisms are proposed for transduction and amplification of the signal induced by GTP binding as well as for the intrinsic and effector-enhanced GTPase activity of EF-Tu. Comparison of the structure with that of EF-Tu-GDP reveals major mutual rearrangements of the three domains of the molecule.
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Affiliation(s)
- H Berchtold
- Central Research G 865A, Hoechst Aktiengesellschaft, Frankfurt, Germany
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725
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Abstract
Tumors of the human thyroid follicular cell demonstrate multiple "routes" and multiple stages of development, offering an unparalleled opportunity for correlating clinicopathologic tumor behavior with the underlying molecular genetic abnormalities. This review summarizes the clinical and experimental evidence supporting the causal role of five key genes in thyroid oncogenesis, namely, the oncogenes ras, gsp, ret, and trk, and the tumor-suppressor gene TP53. The nature of the somatic mutations is described and the likely mechanisms discussed by which they perturb cellular growth signal transduction to produce particular pathologic phenotypes. A model of thyroid oncogenesis is presented that suggests that the pattern of tumor development is determined by the nature of the initiating oncogenic event.
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Affiliation(s)
- D Wynford-Thomas
- David Wynford-Thomas is at the Cancer Research Campaign Thyroid Tumour Biology Research Group, Department of Pathology, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN, WalesUK
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726
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Identification of a small GTP-binding protein, Rab25, expressed in the gastrointestinal mucosa, kidney, and lung. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(17)46639-7] [Citation(s) in RCA: 122] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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727
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Cannon JF. AMBER force-field parameters for guanosine triphosphate and its imido and methylene analogs. J Comput Chem 1993. [DOI: 10.1002/jcc.540140815] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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728
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Moore KJ, Webb MR, Eccleston JF. Mechanism of GTP hydrolysis by p21N-ras catalyzed by GAP: studies with a fluorescent GTP analogue. Biochemistry 1993; 32:7451-9. [PMID: 8338843 DOI: 10.1021/bi00080a016] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The mechanism of the hydrolysis of GTP by p21N-ras and its activation by the catalytic domain of p120 GTPase activating protein (GAP) have been studied using a combination of chemical and fluorescence measurements with the fluorescent GTP analogue, 2'(3')-O-(N-methylanthraniloyl)GTP (mantGTP). Since the concentration of active p21 is important in these measurements, various assays for both total protein and active p21 were investigated. All assays gave good agreement except the filter binding assay of [3H]-GDP bound to p21, which gave values of 35-40% compared to the other methods. Concentrations of p21 were thus based on the absorbance of the mant-chromophore of the p21-mant-nucleotide complexes. The rate constants of the elementary steps of the p21 intrinsic GTPase activity and the GAP activated activity were similar between GTP and mantGTP. Incubation of a stoichiometric complex of p21.mantGTP results in a biphasic decrease in fluorescence. The second phase occurs with the same rate constant as the cleavage step and is accelerated by GAP. No other steps of the mechanism are affected by GAP. Incubation of a stoichiometric complex of p21.mantGpp[NH]p also results in a biphasic decrease in fluorescence even though cleavage does not occur. This is interpreted that the cleavage step of p21.GTP is preceded by and controlled by an isomerization of the p21.GTP complex. GAP accelerates the rate constant of the second fluorescence phase occurring with p21.mantGpp[NH]p. This result shows that GAP accelerates the proposed isomerization which limits GTP cleavage rather than the cleavage step itself.
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Affiliation(s)
- K J Moore
- Division of Physical Biochemistry, National Institute for Medical Research, Mill Hill, London, U.K
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729
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Miller AF, Halkides CJ, Redfield AG. An NMR comparison of the changes produced by different guanosine 5'-triphosphate analogs in wild-type and oncogenic mutant p21ras. Biochemistry 1993; 32:7367-76. [PMID: 8338834 DOI: 10.1021/bi00080a006] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have used nuclear magnetic resonance spectroscopy to compare the conformational changes produced by replacement of bound GDP by the GTP analogs guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and guanylyl (beta, gamma-imido)diphosphate (GMPPNP) in wild-type p21ras as well as the oncogenic mutant (G12D)p21ras. We have used isotope-edited nuclear magnetic resonance spectroscopy to observe the amide resonances of selectively [15N]glycine and [15N]isoleucine labeled p21ras-nucleotide complexes. We find that eight of the nine resonances that respond strongly to GTP gamma S and GMPPNP binding are the same but that the nature of the effect appears different. With GTP gamma S, seven new resonances replace the eight resonances specifically associated with GDP-p21ras, but in GMPPNP-p21ras only two resonances replace the GDP-specific resonances that are lost. The resonance of Gly 60 is clearly shown to be responsive to replacement of GDP by GMPPNP, in addition to glycines 10, 12, 13, 15, and 75 and isoleucines 36, 21, and one other, that were found to respond to GTP gamma S by Miller et al. [Miller, A.-F., Papastavros, M. Z., & Redfield, A.G. (1992) Biochemistry 31, 10208-10216). The two GMPPNP-specific resonances observed appear in positions similar to GTP gamma S-specific resonances, and the GTP gamma S-specific resonances, although not lost altogether, are weaker than the GDP-specific resonances they replace. Thus, the two GTP analogs have similar effects on the spectrum of p21ras, suggesting that the effects are due to features common to both analogs. We propose that active site resonance intensities are specifically attenuated when GTP analogs are bound because interactions with the gamma-phosphate of GTP analogs couple the flexible loops 2 and 4 to the rigid loop 1 of the active site. The conformational heterogeneity and dynamics of loops 2 and 4 would be constrained by loop 1 but also transmitted to it. Coupled conformational exchange on a common intermediate time scale could explain the simultaneous loss of resonances from all three loops in the active site. In our comparison of wild-type and (G12D) GDP-p21ras, we find that the resonance of Ile 36 is not visible in (G12D)p21ras. In (G12D)p21ras, replacement of GDP by GTP gamma S causes the resonances of glycines 10, 13, 15, 60, and 75 and isoleucine 21 and four others to shift from their GDP-specific positions. GTP gamma S-specific resonances are observed for all but two of these.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A F Miller
- Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254
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730
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Löw A, Sprinzl M, Faulhammer HG. Affinity labeling of c-H-ras p21 consensus elements with periodate-oxidized GDP and GTP. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 215:473-9. [PMID: 8393791 DOI: 10.1111/j.1432-1033.1993.tb18056.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The amino acid sequence motifs of human c-H-ras p21 involved in the interaction with guanosine nucleotides were cross-linked to in situ periodate-oxidized [alpha-32P]GDP or [alpha-32P]GTP. Site-specific reaction was achieved by cross-linking conserved lysine residues close to the G-nucleotide binding site of p21 with the 2',3'-dialdehyde derivatives of GDP or GTP under kinetically controlled conditions. After endoproteinase Asp-N digestion, HPLC separation of 32P-labeled peptides and N-terminal microsequence analysis, two single lysine residues, namely, K117 and K147, which are parts of the N-K-X-D and S-A-K/L consensus elements of ras proteins, respectively, were identified. No significant divergences in the position and extent of covalent modification could be detected between p21.GDP and p21.GTP. This is in contrast to Thermus thermophilus EF-Tu.GDP and EF-Tu.GTP, which were investigated with the same technique [Peter, M. E., Wittmann-Liebold, B. & Sprinzl, M. (1988) Biochemistry 27, 9132-9139] and which exhibited considerable differences in cross-linking efficiency in the GTP form as compared to the GDP form of the protein. The described affinity labeling technique of cross-linking [alpha-32P]GTP with GTP-binding proteins can be used as a general analytical method for the detection and identification of consensus elements in GTPases from different organisms.
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Affiliation(s)
- A Löw
- Laboratorium für Biochemie, Universität Bayreuth, Germany
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731
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Hu JS, Redfield AG. Mapping the nucleotide-dependent conformational change of human N-ras p21 in solution by heteronuclear-edited proton-observed NMR methods. Biochemistry 1993; 32:6763-72. [PMID: 8329399 DOI: 10.1021/bi00077a031] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Heteronuclear-edited proton-detected NMR methods are used to study the nucleotide-dependent conformational change between GDP- and GTP gamma S-bound forms of human N-ras p21. Amide groups of Asp are used as sensitive probes. When GTP gamma S is substituted for GDP in cellular N-ras p21, the chemical shifts of resonances Asp-47, -126, -154, and Asn-172, as well as Gly-77 and -151, are not sensitive to nucleotide exchange, whereas Asp-30, -33, -38, -54, -57, -69, -92, -105, and -119 are affected. Distinct chemical shift changes of Asp-33, -38, and -69 indicate that substantial structure changes occur in the effector-binding region and the switch II region. Crystallographic studies of H-ras p21 have indicated that the conformational differences are confined to residues 32-38 and 60-76. Our observations indicate that the nucleotide-dependent structural transitions of the protein in solution may not be identical to those in the crystal. They suggest that the peptide beyond Glu-76 participates in a conformational switch, and possibly is involved in effector function. We propose that the region roughly from Asp-92 to -105, and the region of guanine base-binding motif(s), e.g., 116NKXD, are candidate sites recognized by either a GDP/GTP release factor or a GTPase-affected protein.
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Affiliation(s)
- J S Hu
- Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254
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732
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ATP hydrolysis-linked structural changes in the N-terminal part of the gamma subunit of Escherichia coli F1-ATPase examined by cross-linking studies. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)82368-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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733
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Abstract
Genetic, physical and biochemical methods have been used successfully to identify discrete regions of the p21ras protein involved in protein-protein interactions. Of special interest are the effector residues of p21ras, which are essential for downstream signalling. This review details current understanding of what these residues are and how they bind and activate proteins essential to the ras pathway.
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Affiliation(s)
- M S Marshall
- Department of Medicine, Indiana University School of Medicine, Indianapolis
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734
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Bourret R, Drake S, Chervitz S, Simon M, Falke J. Activation of the phosphosignaling protein CheY. II. Analysis of activated mutants by 19F NMR and protein engineering. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)38623-5] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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735
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Activation of the phosphosignaling protein CheY. I. Analysis of the phosphorylated conformation by 19F NMR and protein engineering. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)38622-3] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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736
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Noda M. Structures and functions of the K rev-1 transformation suppressor gene and its relatives. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1155:97-109. [PMID: 8504133 DOI: 10.1016/0304-419x(93)90024-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- M Noda
- Department of Viral Oncology, Cancer Institute, Japanese Foundation for Cancer Research, Tokyo, Japan
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737
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Newman CM, Magee AI. Posttranslational processing of the ras superfamily of small GTP-binding proteins. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1155:79-96. [PMID: 8504132 DOI: 10.1016/0304-419x(93)90023-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- C M Newman
- Laboratory of Eukaryotic Molecular Genetics, National Institute for Medical Research, Mill Hill, London, UK
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738
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Conklin BR, Bourne HR. Structural elements of G alpha subunits that interact with G beta gamma, receptors, and effectors. Cell 1993; 73:631-41. [PMID: 8388779 DOI: 10.1016/0092-8674(93)90245-l] [Citation(s) in RCA: 329] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- B R Conklin
- Department of Pharmacology, University of California School of Medicine, San Francisco 94143
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739
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Polakis P, McCormick F. Structural requirements for the interaction of p21ras with GAP, exchange factors, and its biological effector target. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)98325-0] [Citation(s) in RCA: 131] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
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740
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Lütcke A, Jansson S, Parton RG, Chavrier P, Valencia A, Huber LA, Lehtonen E, Zerial M. Rab17, a novel small GTPase, is specific for epithelial cells and is induced during cell polarization. J Biophys Biochem Cytol 1993; 121:553-64. [PMID: 8486736 PMCID: PMC2119572 DOI: 10.1083/jcb.121.3.553] [Citation(s) in RCA: 114] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The rab subfamily of small GTPases has been demonstrated to play an important role in the regulation of membrane traffic in eukaryotic cells. Compared with nonpolarized cells, epithelial cells have distinct apical and basolateral transport pathways which need to be separately regulated. This raises the question whether epithelial cells require specific rab proteins. However, all rab proteins identified so far were found to be equally expressed in polarized and nonpolarized cells. Here we report the identification of rab17, the first epithelial cell-specific small GTPase. Northern blot analysis on various mouse organs, revealed that the rab17 mRNA is present in kidney, liver, and intestine but not in organs lacking epithelial cells nor in fibroblasts. To determine whether rab17 is specific for epithelial cells we studied its expression in the developing kidney. We found that rab17 is absent from the mesenchymal precursors but is induced upon their differentiation into epithelial cells. In situ hybridization studies on the embryonic kidney and intestine revealed that rab17 is restricted to epithelial cells. By immunofluorescence and immunoelectron microscopy on kidney sections, rab17 was localized to the basolateral plasma membrane and to apical tubules. Rab proteins associated with two distinct compartments have been found to regulate transport between them. Therefore, our data suggest that rab17 might be involved in transcellular transport.
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Affiliation(s)
- A Lütcke
- European Molecular Biology Laboratory, Heidelberg, Germany
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741
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Löw A, Sprinzl M, Limmer S. Nucleotide binding and GTP hydrolysis by the 21-kDa product of the c-H-ras gene as monitored by proton-NMR spectroscopy. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 213:781-8. [PMID: 8386636 DOI: 10.1111/j.1432-1033.1993.tb17820.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Proton-NMR signals in the downfield region (below approximately 10 ppm) have been shown to provide a useful spectroscopic window to monitor the binding of guanine nucleotides to the active site of GTP/GDP-binding proteins via H-bonds, as specified here by the 21-kDa product of the c-H-ras gene (p21). The time course of the intensity change of certain peaks upon addition of GTP to nucleotide-free p21 corresponds to the GTP hydrolysis rate as determined by HPLC. Though there are fewer potential H-bond acceptors in the GDP-bound protein than in the GTP complex, more downfield peaks are found in the former complex, suggesting tighter binding of GDP. Moreover, inspection of the downfield proton-NMR spectra permits rapid detection of subtle changes of the active site induced by complexation with slowly hydrolyzing GTP analogues resulting from mutations of the amino acid sequence, especially in the phosphate binding loop. Our studies strongly suggest that no major conformational change of the phosphate-binding region occurs upon nucleotide complexation that precedes the catalytic step. Besides, it is suspected that the Ser17 hydroxyl group is involved in nucleotide binding and GTP hydrolysis.
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Affiliation(s)
- A Löw
- Laboratorium für Biochemie, Universität Bayreuth, Germany
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742
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Brennwald P, Novick P. Interactions of three domains distinguishing the Ras-related GTP-binding proteins Ypt1 and Sec4. Nature 1993; 362:560-3. [PMID: 8464498 DOI: 10.1038/362560a0] [Citation(s) in RCA: 159] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The genes SEC4 and YPT1 encode Ras-related GTP-binding proteins in the yeast Saccharomyces cerevisiae. Ypt1 is necessary for vesicular transport from the endoplasmic reticulum to the Golgi, whereas Sec4 is required for fusion of post-Golgi secretory vesicles to the plasma membrane. Recently, three structural domains have been proposed to specify the stage in cellular transport at which members of the Sec4/Ypt1/Rab family act: the effector domain, the C-terminal hypervariable region, and a region corresponding to loop 7 in the structure of p21ras (ref. 8). Here we use Sec4/Ypt1 chimaeras to show that these three regions cooperate to specify Ypt1 function and that the C-terminal hypervariable region is needed for Ypt1 localization to the Golgi. Unexpectedly, we found that a single chimaera can function as either Ypt1 or Sec4 without missorting carboxypeptidase Y or invertase.
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Affiliation(s)
- P Brennwald
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510
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743
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Abstract
The transition of guanine nucleotide binding proteins between the 'on' (GTP-bound) and 'off' (GDP-bound) states has become a paradigm of molecular switching after a chemical reaction. The mechanism by which the switch signal is transmitted to the downstream recipients in the intracellular signal pathway has been extensively studied by biochemical, biophysical and genetic methods, but a clear picture of this process has yet to emerge. Based on the similarities of ras-p21 and elongation factor Tu we propose here a model of the GDP state of ras-p21 that is in agreement with all relevant experimental evidence. The model provides important clues about: (1) a possible molecular mechanism for signal transmission from the site of GTP hydrolysis to downstream effectors; (2) a major conformational change during signal generation and a key residue involved in this process (Tyr-64); and (3) regions in ras-p21 that can be differentially recognized by binding to external partners in a GTP/GDP state dependent fashion, most notably residues D69, Q70, R73, T74, R102, K104, D105 at the end of the alpha-helices 2 and 3.
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Affiliation(s)
- P F Stouten
- European Molecular Biology Laboratory, Protein Design Group, Heidelberg, Germany
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744
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Sawada T, Sakiyama S, Hiwasa T. v-Ha-Ras insertion/deletion mutants with reduced protease-inhibitory activity have no transforming activity. FEBS Lett 1993; 318:297-300. [PMID: 8440385 DOI: 10.1016/0014-5793(93)80532-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have purified 26 insertion/deletion mutants of v-Ha-ras oncogene products produced by Escherichia coli and investigated their protease-inhibitory activity toward papain and cathepsins B and L. Ki values for papain were relatively similar among the mutants, however, those for cathepsins B and L varied up to 10-fold. Among them, four mutants, 1-48 LIR 54-189, 1-110 LIS 112-189, 1-130 PDQ 146-189 and 1-155 LIR 166-189, showed significant reduction in the inhibitory activity toward cathepsin L and these four mutants have lost transforming activity toward NIH3T3 mouse fibroblasts. However, some other mutants also showed no transforming activity in spite of possession of the potent protease-inhibitory activity, suggesting that the protease-inhibitory activity of Ras might be necessary but not sufficient for its biological activity.
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Affiliation(s)
- T Sawada
- Division of Biochemistry, Chiba Cancer Center Research Institute, Japan
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745
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Chung HH, Benson DR, Schultz PG. Probing the structure and mechanism of Ras protein with an expanded genetic code. Science 1993; 259:806-9. [PMID: 8430333 DOI: 10.1126/science.8430333] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Mutations in Ras protein at positions Gly12 and Gly13 (phosphate-binding loop L1) and at positions Ala59, Gly60, and Gln61 (loop L4) are commonly associated with oncogenic activation. The structural and catalytic roles of these residues were probed with a series of unnatural amino acids that have unusual main chain conformations, hydrogen bonding abilities, and steric features. The properties of wild-type and transforming Ras proteins previously thought to be uniquely associated with the structure of a single amino acid at these positions were retained by mutants that contained a variety of unnatural amino acids. This expanded set of functional mutants provides new insight into the role of loop L4 residues in switch function and suggests that loop L1 may participate in the activation of Ras protein by effector molecules.
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Affiliation(s)
- H H Chung
- Department of Chemistry, University of California, Berkeley 94720
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746
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Moya M, Roberts D, Novick P. DSS4-1 is a dominant suppressor of sec4-8 that encodes a nucleotide exchange protein that aids Sec4p function. Nature 1993; 361:460-3. [PMID: 8429886 DOI: 10.1038/361460a0] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The protein Sec4p plays an essential role at the final stage of the yeast secretory pathway and belongs to the ras superfamily of GTP-binding proteins, more specifically to a branch that includes Ypt1p in Saccharomyces cerevisiae and rab proteins in mammalian cells. GTP-binding proteins change conformation depending on whether GTP or GDP is bound and can thus act as a regulatory switch. The protein remains in its inactive, GDP-bound form until exchange of GTP for GDP allows it to stimulate a downstream effector. This interaction is curtailed by GTP hydrolysis. The rates of nucleotide exchange and GTP hydrolysis can be regulated by interaction with accessory proteins. Although GDP dissociation stimulators (GDS) have been identified that act on members of the ras and rho branches of the superfamily, less is known regarding GDSs that act on members of the Sec4/Ypt1/Rab subgroup. A preliminary characterization of a Rab3A GDP dissociation stimulating activity has been presented. We report here the use of suppressor analysis to clone a gene, dss4, encoding a 17K protein that aids Sec4p action in vivo by functioning as a GDP dissociation stimulator.
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Affiliation(s)
- M Moya
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510
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747
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Domains near ATP gamma phosphate in the catalytic site of H+-ATPase. Model proposed from mutagenesis and inhibitor studies. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53672-3] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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748
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Burns RG, Farrell KW, Surridge CD. Should the tubulins be members of the GTPase superfamily? CIBA FOUNDATION SYMPOSIUM 1993; 176:248-267. [PMID: 8299423 DOI: 10.1002/9780470514450.ch16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The beta-subunit of the alpha/beta tubulin heterodimer resembles other members of the GTPase superfamily in that: it binds GTP, the GTP is hydrolysed to GDP on microtubule assembly and this induces a conformational change; it exhibits a similar nucleotide stereospecificity; aluminium and beryllium fluorides inhibit this hydrolysis-dependent conformational change; and beta-tubulin contains peptides which are similar to the consensus motifs characteristic of the GTPase superfamily proteins. By contrast, UV photo-cross-linking and other binding studies have identified peptides which may contribute to the GTP-binding site but which are absent from the GTPase superfamily proteins. We suggest that beta-tubulin has a 'dual personality', with the characteristics of the GTP-binding site depending upon the precise conformation of the protein and upon whether the experimental assays probe nucleotide binding or the hydrolytic mechanism. We suggest that the hydrolytic mechanism of beta-tubulin resembles that of the other members of the GTPase superfamily, although the differences within the consensus motifs dictate that the architecture of the GTP pocket cannot be identical.
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Affiliation(s)
- R G Burns
- Blackett Laboratory, Imperial College of Science, Technology and Medicine, London, UK
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749
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John J, Rensland H, Schlichting I, Vetter I, Borasio G, Goody R, Wittinghofer A. Kinetic and structural analysis of the Mg(2+)-binding site of the guanine nucleotide-binding protein p21H-ras. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)54022-9] [Citation(s) in RCA: 204] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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750
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Abstract
Rhodopsin, upon activation by light, transduces the photon signal by activation of the G-protein, transducin. The well-studied rhodopsin/transducin system serves as a model for the understanding of signal transduction by the large class of G-protein-coupled receptors. The interactive form of rhodopsin, R*, is conformationally similar or identical to rhodopsin's photolysis intermediate Metarhodopsin II (MII). Formation of MII requires deprotonation of rhodopsin's protonated Schiff base which appears to facilitate some opening of the rhodopsin structure. This allows a change in conformation at rhodopsin's cytoplasmic surface that provides binding sites for transducin. Rhodopsin's 2nd, 3rd and putative 4th cytoplasmic loops bind transducin at sites including transducin's 5 kDa carboxyl-terminal region. Site-specific mutagenesis of rhodopsin is being used to distinguish sites on rhodopsin's surface that are important in binding transducin from those that function in activating transducin. These observations are consistent with and extend studies on the action of other G-protein-coupled receptors and their interactions with their respective G proteins.
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Affiliation(s)
- P A Hargrave
- Department of Ophthalmology, University of Florida, Gainesville 32610
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