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Expanding the Clinical and Genetic Spectrum of RAB28-Related Cone-Rod Dystrophy: Pathogenicity of Novel Variants in Italian Families. Int J Mol Sci 2020; 22:ijms22010381. [PMID: 33396523 PMCID: PMC7795990 DOI: 10.3390/ijms22010381] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Revised: 12/28/2020] [Accepted: 12/28/2020] [Indexed: 12/11/2022] Open
Abstract
The small Ras-related GTPase Rab-28 is highly expressed in photoreceptor cells, where it possibly participates in membrane trafficking. To date, six alterations in the RAB28 gene have been associated with autosomal recessive cone-rod dystrophies. Confirmed variants include splicing variants, missense and nonsense mutations. Here, we present a thorough phenotypical and genotypical characterization of five individuals belonging to four Italian families, constituting the largest cohort of RAB28 patients reported in literature to date. All probands displayed similar clinical phenotype consisting of photophobia, decreased visual acuity, central outer retinal thinning, and impaired color vision. By sequencing the four probands, we identified: a novel homozygous splicing variant; two novel nonsense variants in homozygosis; a novel missense variant in compound heterozygous state with a previously reported nonsense variant. Exhaustive molecular dynamics simulations of the missense variant p.(Thr26Asn) in both its active and inactive states revealed an allosteric structural mechanism that impairs the binding of Mg2+, thus decreasing the affinity for GTP. The impaired GTP-GDP exchange ultimately locks Rab-28 in a GDP-bound inactive state. The loss-of-function mutation p.(Thr26Asn) was present in a compound heterozygosis with the nonsense variant p.(Arg137*), which does not cause mRNA-mediated decay, but is rather likely degraded due to its incomplete folding. The frameshift p.(Thr26Valfs4*) and nonsense p.(Leu13*) and p.(Trp107*) variants, if translated, would lack several key structural components necessary for the correct functioning of the encoded protein.
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Génier S, Létourneau D, Gauthier E, Picard S, Boisvert M, Parent JL, Lavigne P. In-depth NMR characterization of Rab4a structure, nucleotide exchange and hydrolysis kinetics reveals an atypical GTPase profile. J Struct Biol 2020; 212:107582. [PMID: 32707235 DOI: 10.1016/j.jsb.2020.107582] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 07/15/2020] [Accepted: 07/17/2020] [Indexed: 10/23/2022]
Abstract
Rab4a is a small GTPase associated with endocytic compartments and a key regulator of early endosomes recycling. Gathering evidence indicates that its expression and activation are required for the development of metastases. Rab4a-intrinsic GTPase properties that control its activity, i.e. nucleotide exchange and hydrolysis rates, have not yet been thoroughly studied. The determination of these properties is of the utmost importance to understand its functions and contributions to tumorigenesis. Here, we used the constitutively active (Rab4aQ67L) and dominant negative (Rab4aS22N) mutants to characterize the thermodynamical and structural determinants of the interaction between Rab4a and GTP (GTPγS) as well as GDP. We report the first 1H, 13C, 15N backbone NMR assignments of a Rab GTPase family member with Rab4a in complex with GDP and GTPγS. We also provide a qualitative description of the extent of structural and dynamical changes caused by the Q67L and S22N mutations. Using a real-time NMR approach and the two aforementioned mutants as controls, we evaluated Rab4a intrinsic nucleotide exchange and hydrolysis rates. Compared to most small GTPases such as Ras, a rapid GTP exchange rate along with slow hydrolysis rate were observed. This suggests that, in a cellular context, Rab4a can self-activate and persist in an activated state in absence of regulatory mechanisms. This peculiar profile is uncommon among the Ras superfamily members, making Rab4a an atypical fast-cycling GTPase and may explain, at least in part, how it contributes to metastases.
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Affiliation(s)
- Samuel Génier
- Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada; Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada
| | - Danny Létourneau
- Département de Biochimie et Génomique Fonctionnelle, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada; Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada
| | - Esther Gauthier
- Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada; Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada
| | - Samuel Picard
- Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada; Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada
| | - Marilou Boisvert
- Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada; Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada
| | - Jean-Luc Parent
- Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada; Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada.
| | - Pierre Lavigne
- Département de Biochimie et Génomique Fonctionnelle, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada; Institut de Pharmacologie de Sherbrooke, Sherbrooke, Québec, Canada.
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3
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Yoo DY, Hauser AD, Joy ST, Bar-Sagi D, Arora PS. Covalent Targeting of Ras G12C by Rationally Designed Peptidomimetics. ACS Chem Biol 2020; 15:1604-1612. [PMID: 32378881 PMCID: PMC7739374 DOI: 10.1021/acschembio.0c00204] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Protein-protein interactions (PPIs) play a critical role in fundamental biological processes. Competitive inhibition of these interfaces requires compounds that can access discontinuous binding epitopes along a large, shallow binding surface area. Conformationally defined protein surface mimics present a viable route to target these interactions. However, the development of minimal protein mimics that engage intracellular targets with high affinity remains a major challenge because mimicry of a portion of the binding interface is often associated with the loss of critical binding interactions. Covalent targeting provides an attractive approach to overcome the loss of noncovalent contacts but have the inherent risk of dominating noncovalent contacts and increasing the likelihood of nonselective binding. Here, we report the iterative design of a proteolytically stable α3β chimeric helix mimic that covalently targets oncogenic Ras G12C as a model system. We explored several electrophiles to optimize preferential alkylation with the desired C12 on Ras. The designed lead peptide modulates nucleotide exchange, inhibits activation of the Ras-mediated signaling cascade, and is selectively toxic toward mutant Ras G12C cancer cells. The relatively high frequency of acquired cysteines as missense mutations in cancer and other diseases suggests that covalent peptides may offer an untapped therapeutic approach for targeting aberrant protein interactions.
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Affiliation(s)
- Daniel Y. Yoo
- Department of Chemistry, New York University, New York, 10003, U.S.A
| | - Andrew D. Hauser
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, U.S.A
| | - Stephen T. Joy
- Department of Chemistry, New York University, New York, 10003, U.S.A
| | - Dafna Bar-Sagi
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, U.S.A
| | - Paramjit S. Arora
- Department of Chemistry, New York University, New York, 10003, U.S.A
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Fukushima Y, Nishiyama K, Kataoka H, Fruttiger M, Fukuhara S, Nishida K, Mochizuki N, Kurihara H, Nishikawa SI, Uemura A. RhoJ integrates attractive and repulsive cues in directional migration of endothelial cells. EMBO J 2020; 39:e102930. [PMID: 32347571 DOI: 10.15252/embj.2019102930] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 03/30/2020] [Accepted: 04/03/2020] [Indexed: 12/19/2022] Open
Abstract
During angiogenesis, VEGF acts as an attractive cue for endothelial cells (ECs), while Sema3E mediates repulsive cues. Here, we show that the small GTPase RhoJ integrates these opposing signals in directional EC migration. In the GTP-bound state, RhoJ interacts with the cytoplasmic domain of PlexinD1. Upon Sema3E stimulation, RhoJ released from PlexinD1 induces cell contraction. PlexinD1-bound RhoJ further facilitates Sema3E-induced PlexinD1-VEGFR2 association, VEGFR2 transphosphorylation at Y1214, and p38 MAPK activation, leading to reverse EC migration. Upon VEGF stimulation, RhoJ is required for the formation of the holoreceptor complex comprising VEGFR2, PlexinD1, and neuropilin-1, thereby preventing degradation of internalized VEGFR2, prolonging downstream signal transductions via PLCγ, Erk, and Akt, and promoting forward EC migration. After conversion to the GDP-bound state, RhoJ shifts from PlexinD1 to VEGFR2, which then terminates the VEGFR2 signals. RhoJ deficiency in ECs efficiently suppressed aberrant angiogenesis in ischemic retina. These findings suggest that distinct Rho GTPases may act as context-dependent integrators of chemotactic cues in directional cell migration and may serve as candidate therapeutic targets to manipulate cell motility in disease or tissue regeneration.
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Affiliation(s)
- Yoko Fukushima
- Division of Vascular Biology, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan.,Department of Ophthalmology, Osaka University Graduate School of Medicine, Osaka, Japan
| | - Koichi Nishiyama
- International Research Center for Medical Sciences, Kumamoto University, Kumamoto, Japan
| | - Hiroshi Kataoka
- Laboratory for Stem Cell Biology, RIKEN Center for Developmental Biology, Kobe, Japan
| | - Marcus Fruttiger
- UCL Institute of Ophthalmology, University College London, London, UK
| | - Shigetomo Fukuhara
- Department of Molecular Pathophysiology, Institute for Advanced Medical Sciences, Nippon Medical School, Kawasaki, Japan
| | - Kohji Nishida
- Department of Ophthalmology, Osaka University Graduate School of Medicine, Osaka, Japan
| | - Naoki Mochizuki
- Department of Cell Biology, National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan
| | - Hiroki Kurihara
- Department of Physiological Chemistry and Metabolism, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Shin-Ichi Nishikawa
- Laboratory for Stem Cell Biology, RIKEN Center for Developmental Biology, Kobe, Japan
| | - Akiyoshi Uemura
- Division of Vascular Biology, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe, Japan.,Department of Retinal Vascular Biology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan
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5
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Bocanegra JL, Fujita BM, Melton NR, Cowan JM, Schinski EL, Tamir TY, Major MB, Quintero OA. The MyMOMA domain of MYO19 encodes for distinct Miro-dependent and Miro-independent mechanisms of interaction with mitochondrial membranes. Cytoskeleton (Hoboken) 2020; 77:149-166. [PMID: 31479585 PMCID: PMC8556674 DOI: 10.1002/cm.21560] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 08/13/2019] [Accepted: 08/31/2019] [Indexed: 08/19/2023]
Abstract
MYO19 interacts with mitochondria through a C-terminal membrane association domain (MyMOMA). Specific mechanisms for localization of MYO19 to mitochondria are poorly understood. Using promiscuous biotinylation data in combination with existing affinity-capture databases, we have identified a number of putative MYO19-interacting proteins. We chose to explore the interaction between MYO19 and the mitochondrial GTPase Miro2 by expressing mchr-Miro2 in combination with GFP-tagged fragments of the MyMOMA domain and assaying for recruitment of MYO19-GFP to mitochondria. Coexpression of MYO19898-970 -GFP with mchr-Miro2 enhanced MYO19898-970 -GFP localization to mitochondria. Mislocalizing Miro2 to filopodial tips or the cytosolic face of the nuclear envelope did not recruit MYO19898-970 -GFP to either location. To address the kinetics of the Miro2/MYO19 interaction, we used FRAP analysis and permeabilization-activated reduction in fluorescence analysis. MyMOMA constructs containing a putative membrane-insertion motif but lacking the Miro2-interacting region displayed slow exchange kinetics. MYO19898-970 -GFP, which does not include the membrane-insertion motif, displayed rapid exchange kinetics, suggesting that MYO19 interacting with Miro2 has higher mobility than MYO19 inserted into the mitochondrial outer membrane. Mutation of well-conserved, charged residues within MYO19 or within the switch I and II regions of Miro2 abolished the enhancement of MYO19898-970 -GFP localization in cells ectopically expressing mchr-Miro2. Additionally, expressing mutant versions of Miro2 thought to represent particular nucleotide states indicated that the enhancement of MYO19898-970 -GFP localization is dependent on Miro2 nucleotide state. Taken together, these data suggest that membrane-inserted MYO19 is part of a larger complex, and that Miro2 plays a role in integration of actin- and microtubule-based mitochondrial activities.
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Affiliation(s)
| | | | | | - James M. Cowan
- Department of Biology, University of Richmond, Richmond, Virginia
| | | | - Tigist Y. Tamir
- Department of Pharmacology, University of North Carolina Chapel Hill, Chapel Hill, North Carolina
| | - Michael B. Major
- Department of Pharmacology, University of North Carolina Chapel Hill, Chapel Hill, North Carolina
- Department of Cell Biology and Physiology, University of North Carolina Chapel Hill, Chapel Hill, North Carolina
- Lineberger Comprehensive Cancer Center, University of North Carolina Chapel Hill, Chapel Hill, North Carolina
| | - Omar A. Quintero
- Department of Biology, University of Richmond, Richmond, Virginia
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Bery N, Keller L, Soulié M, Gence R, Iscache AL, Cherier J, Cabantous S, Sordet O, Lajoie-Mazenc I, Pedelacq JD, Favre G, Olichon A. A Targeted Protein Degradation Cell-Based Screening for Nanobodies Selective toward the Cellular RHOB GTP-Bound Conformation. Cell Chem Biol 2019; 26:1544-1558.e6. [PMID: 31522999 DOI: 10.1016/j.chembiol.2019.08.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2018] [Revised: 11/22/2018] [Accepted: 08/23/2019] [Indexed: 01/10/2023]
Abstract
The selective downregulation of activated intracellular proteins is a key challenge in cell biology. RHO small GTPases switch between a guanosine diphosphate (GDP)-bound and a guanosine triphosphate (GTP)-bound state that drives downstream signaling. At present, no tool is available to study endogenous RHO-GTPinduced conformational changes in live cells. Here, we established a cell-based screen to selectively degrade RHOB-GTP using F-box-intracellular single-domain antibody fusion. We identified one intracellular antibody (intrabody) that shows selective targeting of endogenous RHOB-GTP mediated by interactions between the CDR3 loop of the domain antibody and the GTP-binding pocket of RHOB. Our results suggest that, while RHOB is highly regulated at the expression level, only the GTP-bound pool, but not its global expression, mediates RHOB functions in genomic instability and in cell invasion. The F-box/intrabody-targeted protein degradation represents a unique approach to knock down the active form of small GTPases or other proteins with multiple cellular activities.
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Affiliation(s)
- Nicolas Bery
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Laura Keller
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France; Département de Biologie, Institut Claudius Regaud, Toulouse, France
| | - Marjorie Soulié
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Rémi Gence
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Anne-Laure Iscache
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France; Département de Biologie, Institut Claudius Regaud, Toulouse, France
| | - Julia Cherier
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France; Département de Biologie, Institut Claudius Regaud, Toulouse, France
| | - Stéphanie Cabantous
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Olivier Sordet
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Isabelle Lajoie-Mazenc
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Jean-Denis Pedelacq
- Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, Toulouse, France.
| | - Gilles Favre
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France; Département de Biologie, Institut Claudius Regaud, Toulouse, France.
| | - Aurélien Olichon
- Centre de Recherche en Cancérologie de Toulouse (CRCT), INSERM, Université de Toulouse, CNRS, UPS, Toulouse, France.
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7
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Cleator JH, Wells CA, Dingus J, Kurtz DT, Hildebrandt JD. The N54- αs Mutant Has Decreased Affinity for βγ and Suggests a Mechanism for Coupling Heterotrimeric G Protein Nucleotide Exchange with Subunit Dissociation. J Pharmacol Exp Ther 2018; 365:219-225. [PMID: 29491039 DOI: 10.1124/jpet.117.245779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 02/23/2018] [Indexed: 11/22/2022] Open
Abstract
Ser54 of Gsα binds guanine nucleotide and Mg2+ as part of a conserved sequence motif in GTP binding proteins. Mutating the homologous residue in small and heterotrimeric G proteins generates dominant-negative proteins, but by protein-specific mechanisms. For αi/o, this results from persistent binding of α to βγ, whereas for small GTP binding proteins and αs this results from persistent binding to guanine nucleotide exchange factor or receptor. This work examined the role of βγ interactions in mediating the properties of the Ser54-like mutants of Gα subunits. Unexpectedly, WT-αs or N54-αs coexpressed with α1B-adrenergic receptor in human embryonic kidney 293 cells decreased receptor stimulation of IP3 production by a cAMP-independent mechanism, but WT-αs was more effective than the mutant. One explanation for this result would be that αs, like Ser47 αi/o, blocks receptor activation by sequestering βγ; implying that N54-αS has reduced affinity for βγ since it was less effective at blocking IP3 production. This possibility was more directly supported by the observation that WT-αs was more effective than the mutant in inhibiting βγ activation of phospholipase Cβ2. Further, in vitro synthesized N54-αs bound biotinylated-βγ with lower apparent affinity than did WT-αs The Cys54 mutation also decreased βγ binding but less effectively than N54-αs Substitution of the conserved Ser in αo with Cys or Asn increased βγ binding, with the Cys mutant being more effective. This suggests that Ser54 of αs is involved in coupling changes in nucleotide binding with altered subunit interactions, and has important implications for how receptors activate G proteins.
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Affiliation(s)
- John H Cleator
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - Christopher A Wells
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - Jane Dingus
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - David T Kurtz
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
| | - John D Hildebrandt
- Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina
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Mayers JR, Hu T, Wang C, Cárdenas JJ, Tan Y, Pan J, Bednarek SY. SCD1 and SCD2 Form a Complex That Functions with the Exocyst and RabE1 in Exocytosis and Cytokinesis. THE PLANT CELL 2017; 29:2610-2625. [PMID: 28970336 PMCID: PMC5774579 DOI: 10.1105/tpc.17.00409] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 09/12/2017] [Accepted: 09/26/2017] [Indexed: 05/21/2023]
Abstract
Although exocytosis is critical for the proper trafficking of materials to the plasma membrane, relatively little is known about the mechanistic details of post-Golgi trafficking in plants. Here, we demonstrate that the DENN (Differentially Expressed in Normal and Neoplastic cells) domain protein STOMATAL CYTOKINESIS DEFECTIVE1 (SCD1) and SCD2 form a previously unknown protein complex, the SCD complex, that functionally interacts with subunits of the exocyst complex and the RabE1 family of GTPases in Arabidopsis thaliana Consistent with a role in post-Golgi trafficking, scd1 and scd2 mutants display defects in exocytosis and recycling of PIN2-GFP. Perturbation of exocytosis using the small molecule Endosidin2 results in growth inhibition and PIN2-GFP trafficking defects in scd1 and scd2 mutants. In addition to the exocyst, the SCD complex binds in a nucleotide state-specific manner with Sec4p/Rab8-related RabE1 GTPases and overexpression of wild-type RabE1 rescues scd1 temperature-sensitive mutants. Furthermore, SCD1 colocalizes with the exocyst subunit, SEC15B, and RabE1 at the cell plate and in distinct punctae at or near the plasma membrane. Our findings reveal a mechanism for plant exocytosis, through the identification and characterization of a protein interaction network that includes the SCD complex, RabE1, and the exocyst.
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Affiliation(s)
| | - Tianwei Hu
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Chao Wang
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Jessica J Cárdenas
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Yuqi Tan
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Jianwei Pan
- Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
- College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China
| | - Sebastian Y Bednarek
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
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9
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Francis JW, Goswami D, Novick SJ, Pascal BD, Weikum ER, Ortlund EA, Griffin PR, Kahn RA. Nucleotide Binding to ARL2 in the TBCD∙ARL2∙β-Tubulin Complex Drives Conformational Changes in β-Tubulin. J Mol Biol 2017; 429:3696-3716. [PMID: 28970104 DOI: 10.1016/j.jmb.2017.09.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Revised: 08/31/2017] [Accepted: 09/26/2017] [Indexed: 11/25/2022]
Abstract
Microtubules are highly dynamic tubulin polymers that are required for a variety of cellular functions. Despite the importance of a cellular population of tubulin dimers, we have incomplete information about the mechanisms involved in the biogenesis of αβ-tubulin heterodimers. In addition to prefoldin and the TCP-1 Ring Complex, five tubulin-specific chaperones, termed cofactors A-E (TBCA-E), and GTP are required for the folding of α- and β-tubulin subunits and assembly into heterodimers. We recently described the purification of a novel trimer, TBCD•ARL2•β-tubulin. Here, we employed hydrogen/deuterium exchange coupled with mass spectrometry to explore the dynamics of each of the proteins in the trimer. Addition of guanine nucleotides resulted in changes in the solvent accessibility of regions of each protein that led to predictions about each's role in tubulin folding. Initial testing of that model confirmed that it is ARL2, and not β-tubulin, that exchanges GTP in the trimer. Comparisons of the dynamics of ARL2 monomer to ARL2 in the trimer suggested that its protein interactions were comparable to those of a canonical GTPase with an effector. This was supported by the use of nucleotide-binding assays that revealed an increase in the affinity for GTP by ARL2 in the trimer. We conclude that the TBCD•ARL2•β-tubulin complex represents a functional intermediate in the β-tubulin folding pathway whose activity is regulated by the cycling of nucleotides on ARL2. The co-purification of guanine nucleotide on the β-tubulin in the trimer is also shown, with implications to modeling the pathway.
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Affiliation(s)
- Joshua W Francis
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, United States
| | - Devrishi Goswami
- Department of Molecular Medicine, The Scripps Research Institute, Jupiter, FL 33458, United States
| | - Scott J Novick
- Department of Molecular Medicine, The Scripps Research Institute, Jupiter, FL 33458, United States
| | - Bruce D Pascal
- Department of Molecular Medicine, The Scripps Research Institute, Jupiter, FL 33458, United States
| | - Emily R Weikum
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, United States
| | - Eric A Ortlund
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, United States
| | - Patrick R Griffin
- Department of Molecular Medicine, The Scripps Research Institute, Jupiter, FL 33458, United States
| | - Richard A Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322, United States.
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10
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The Architecture of the Rag GTPase Signaling Network. Biomolecules 2017; 7:biom7030048. [PMID: 28788436 PMCID: PMC5618229 DOI: 10.3390/biom7030048] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Revised: 06/22/2017] [Accepted: 06/27/2017] [Indexed: 12/11/2022] Open
Abstract
The evolutionarily conserved target of rapamycin complex 1 (TORC1) couples an array of intra- and extracellular stimuli to cell growth, proliferation and metabolism, and its deregulation is associated with various human pathologies such as immunodeficiency, epilepsy, and cancer. Among the diverse stimuli impinging on TORC1, amino acids represent essential input signals, but how they control TORC1 has long remained a mystery. The recent discovery of the Rag GTPases, which assemble as heterodimeric complexes on vacuolar/lysosomal membranes, as central elements of an amino acid signaling network upstream of TORC1 in yeast, flies, and mammalian cells represented a breakthrough in this field. Here, we review the architecture of the Rag GTPase signaling network with a special focus on structural aspects of the Rag GTPases and their regulators in yeast and highlight both the evolutionary conservation and divergence of the mechanisms that control Rag GTPases.
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11
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Morris KM, Henderson R, Suresh Kumar TK, Heyes CD, Adams PD. Intrinsic GTP hydrolysis is observed for a switch 1 variant of Cdc42 in the presence of a specific GTPase inhibitor. Small GTPases 2016; 7:1-11. [PMID: 26828437 DOI: 10.1080/21541248.2015.1123797] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The Ras-related protein Cell division cycle 42 (Cdc42) is important in cell-signaling processes. Protein interactions involving Cdc42 occur primarily in flexible "Switch" regions that help regulate effector binding. We studied the kinetics of intrinsic GTP hydrolysis reaction in the absence and presence of a biologically active peptide derivative of a p21-activated kinase effector (PBD46) for wt Cdc42 and compared it to the Switch 1 variant Cdc42(T35A). While the binding of PBD46 to wt Cdc42 results in complete inhibition of GTP hydrolysis, this interaction in Cdc42(T35A) does not. Comparison of the crystal structure of wt Cdc42 in the absence of effector (1AN0.pdb), as well as the NMR structure of wt Cdc42 bound to an effector in the Switch 1 region (1CF4.pdb) ( www.rcsb.org ) suggests that the orientation of T(35) with bound Mg(2+) changes in the presence of effector, resulting in movement of GTP away from the catalytic box leading to the inhibition of GTP hydrolysis. For Cdc42(T35A), molecular dynamics simulations and structural analyses suggest that the nucleotide does not undergo the conformational shift observed for the wt Cdc42-effector interaction. Our data suggest that change in dynamics in the Switch 1 region of Cdc42 caused by the T35A mutation (Chandrashekar, et al. 2011, Biochemistry, 50, p. 6196) fosters a conformation for this Cdc42 variant that allows hydrolysis of GTP in the presence of PBD46, and that alteration of the conformational dynamics could potentially modulate Ras-related over-activity.
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Affiliation(s)
- Kyla M Morris
- a Department of Chemistry and Biochemistry , University of Arkansas , Fayetteville , Fayetteville , AR , USA
| | - Rory Henderson
- a Department of Chemistry and Biochemistry , University of Arkansas , Fayetteville , Fayetteville , AR , USA
| | | | - Colin D Heyes
- a Department of Chemistry and Biochemistry , University of Arkansas , Fayetteville , Fayetteville , AR , USA
| | - Paul D Adams
- a Department of Chemistry and Biochemistry , University of Arkansas , Fayetteville , Fayetteville , AR , USA
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12
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Okosun J, Wolfson RL, Wang J, Araf S, Wilkins L, Castellano BM, Escudero-Ibarz L, Al Seraihi AF, Richter J, Bernhart SH, Efeyan A, Iqbal S, Matthews J, Clear A, Guerra-Assunção JA, Bödör C, Quentmeier H, Mansbridge C, Johnson P, Davies A, Strefford JC, Packham G, Barrans S, Jack A, Du MQ, Calaminici M, Lister TA, Auer R, Montoto S, Gribben JG, Siebert R, Chelala C, Zoncu R, Sabatini DM, Fitzgibbon J. Recurrent mTORC1-activating RRAGC mutations in follicular lymphoma. Nat Genet 2016; 48:183-8. [PMID: 26691987 PMCID: PMC4731318 DOI: 10.1038/ng.3473] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 11/23/2015] [Indexed: 12/13/2022]
Abstract
Follicular lymphoma is an incurable B cell malignancy characterized by the t(14;18) translocation and mutations affecting the epigenome. Although frequent gene mutations in key signaling pathways, including JAK-STAT, NOTCH and NF-κB, have also been defined, the spectrum of these mutations typically overlaps with that in the closely related diffuse large B cell lymphoma (DLBCL). Using a combination of discovery exome and extended targeted sequencing, we identified recurrent somatic mutations in RRAGC uniquely enriched in patients with follicular lymphoma (17%). More than half of the mutations preferentially co-occurred with mutations in ATP6V1B2 and ATP6AP1, which encode components of the vacuolar H(+)-ATP ATPase (V-ATPase) known to be necessary for amino acid-induced activation of mTORC1. The RagC variants increased raptor binding while rendering mTORC1 signaling resistant to amino acid deprivation. The activating nature of the RRAGC mutations, their existence in the dominant clone and their stability during disease progression support their potential as an excellent candidate for therapeutic targeting.
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Affiliation(s)
- Jessica Okosun
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Rachel L Wolfson
- Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology, Department of Biology, Cambridge, Massachusetts, USA
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Jun Wang
- Centre for Molecular Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Shamzah Araf
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Lucy Wilkins
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Brian M Castellano
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, USA
| | - Leire Escudero-Ibarz
- Division of Molecular Histopathology, Department of Pathology, University of Cambridge, Cambridge, UK
| | - Ahad Fahad Al Seraihi
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Julia Richter
- Institute of Human Genetics, University Hospital Schleswig-Holstein Campus Kiel and Christian Albrechts University Kiel, Kiel, Germany
| | - Stephan H Bernhart
- Transcriptome Bioinformatics, LIFE Research Center for Civilization Diseases, Leipzig, Germany
- Interdisciplinary Center for Bioinformatics, University of Leipzig, Leipzig, Germany
- Bioinformatics Group, Department of Computer Science, University of Leipzig, Leipzig, Germany
| | - Alejo Efeyan
- Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology, Department of Biology, Cambridge, Massachusetts, USA
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Sameena Iqbal
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Janet Matthews
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Andrew Clear
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | | | - Csaba Bödör
- MTA-SE Lendulet Molecular Oncohematology Research Group, 1st Department of Pathology and Experimental Cancer Research, Semmelweis University, Budapest, Hungary
| | - Hilmar Quentmeier
- Leibniz Institute DSMZ, German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany
| | | | - Peter Johnson
- Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Andrew Davies
- Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Jonathan C Strefford
- Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Graham Packham
- Cancer Sciences Unit, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Sharon Barrans
- Haematological Malignancy Diagnostic Service, St. James's Institute of Oncology, Leeds, UK
| | - Andrew Jack
- Haematological Malignancy Diagnostic Service, St. James's Institute of Oncology, Leeds, UK
| | - Ming-Qing Du
- Division of Molecular Histopathology, Department of Pathology, University of Cambridge, Cambridge, UK
| | - Maria Calaminici
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - T Andrew Lister
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Rebecca Auer
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Silvia Montoto
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - John G Gribben
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Reiner Siebert
- Institute of Human Genetics, University Hospital Schleswig-Holstein Campus Kiel and Christian Albrechts University Kiel, Kiel, Germany
| | - Claude Chelala
- Centre for Molecular Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
| | - Roberto Zoncu
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, USA
| | - David M Sabatini
- Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology, Department of Biology, Cambridge, Massachusetts, USA
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Koch Institute for Integrative Cancer Research, Cambridge, Massachusetts, USA
- Broad Institute of Harvard and MIT, Cambridge, Massachusetts, USA
| | - Jude Fitzgibbon
- Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, UK
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13
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Lu S, Jang H, Muratcioglu S, Gursoy A, Keskin O, Nussinov R, Zhang J. Ras Conformational Ensembles, Allostery, and Signaling. Chem Rev 2016; 116:6607-65. [PMID: 26815308 DOI: 10.1021/acs.chemrev.5b00542] [Citation(s) in RCA: 266] [Impact Index Per Article: 33.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Ras proteins are classical members of small GTPases that function as molecular switches by alternating between inactive GDP-bound and active GTP-bound states. Ras activation is regulated by guanine nucleotide exchange factors that catalyze the exchange of GDP by GTP, and inactivation is terminated by GTPase-activating proteins that accelerate the intrinsic GTP hydrolysis rate by orders of magnitude. In this review, we focus on data that have accumulated over the past few years pertaining to the conformational ensembles and the allosteric regulation of Ras proteins and their interpretation from our conformational landscape standpoint. The Ras ensemble embodies all states, including the ligand-bound conformations, the activated (or inactivated) allosteric modulated states, post-translationally modified states, mutational states, transition states, and nonfunctional states serving as a reservoir for emerging functions. The ensemble is shifted by distinct mutational events, cofactors, post-translational modifications, and different membrane compositions. A better understanding of Ras biology can contribute to therapeutic strategies.
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Affiliation(s)
- Shaoyong Lu
- Department of Pathophysiology, Shanghai Universities E-Institute for Chemical Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University, School of Medicine , Shanghai, 200025, China.,Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory, National Cancer Institute , Frederick, Maryland 21702, United States
| | - Hyunbum Jang
- Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory, National Cancer Institute , Frederick, Maryland 21702, United States
| | | | | | | | - Ruth Nussinov
- Cancer and Inflammation Program, Leidos Biomedical Research, Inc., Frederick National Laboratory, National Cancer Institute , Frederick, Maryland 21702, United States.,Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Sackler Institute of Molecular Medicine, Tel Aviv University , Tel Aviv 69978, Israel
| | - Jian Zhang
- Department of Pathophysiology, Shanghai Universities E-Institute for Chemical Biology, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University, School of Medicine , Shanghai, 200025, China
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14
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Gripp KW, Sol-Church K, Smpokou P, Graham GE, Stevenson DA, Hanson H, Viskochil DH, Baker LC, Russo B, Gardner N, Stabley DL, Kolbe V, Rosenberger G. An attenuated phenotype of Costello syndrome in three unrelated individuals with a HRAS c.179G>A (p.Gly60Asp) mutation correlates with uncommon functional consequences. Am J Med Genet A 2015; 167A:2085-97. [PMID: 25914166 DOI: 10.1002/ajmg.a.37128] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Accepted: 04/06/2015] [Indexed: 12/20/2022]
Abstract
Heterozygous germline mutations in the proto-oncogene HRAS cause Costello syndrome (CS), an intellectual disability condition with severe failure to thrive, cardiac abnormalities, predisposition to tumors, and neurologic abnormalities. More than 80% of patients share the HRAS mutation c.34G>A (p.Gly12Ser) associated with the typical, relatively homogeneous phenotype. Rarer mutations occurred in individuals with an attenuated phenotype and less characteristic facial features. Most pathogenic HRAS alterations affect hydrolytic HRAS activity resulting in constitutive activation. "Gain-of-function" and "hyperactivation" concerning downstream pathways are widely used to explain the molecular basis and dysregulation of the RAS-MAPK pathway is the biologic mechanism shared amongst rasopathies. Panel testing for rasopathies identified a novel HRAS mutation (c.179G>A; p.Gly60Asp) in three individuals with attenuated features of Costello syndrome. De novo paternal origin occurred in two, transmission from a heterozygous mother in the third. Individuals showed subtle facial features; curly hair and relative macrocephaly were seen in three; atrial tachycardia and learning difficulties in two, and pulmonic valve dysplasia and mildly thickened left ventricle in one. None had severe failure to thrive, intellectual disability or cancer, underscoring the need to consider HRAS mutations in individuals with an unspecific rasopathy phenotype. Functional studies revealed strongly increased HRAS(Gly60Asp) binding to RAF1, but not to other signaling effectors. Hyperactivation of the MAPK downstream signaling pathways was absent. Our results indicate that an increase in the proportion of activated RAS downstream signaling components does not entirely explain the molecular basis of CS. We conclude that the phenotypic variability in CS recapitulates variable qualities of molecular dysfunction.
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Affiliation(s)
- Karen W Gripp
- Division of Medical Genetics, A. I. duPont Hospital for Children, Wilmington, Delaware
| | - Katia Sol-Church
- Center for Applied Clinical Genomics, A. I. duPont Hospital for Children, Wilmington, Delaware
| | - Patroula Smpokou
- Division of Genetics and Metabolism, Children's National Health System, Washington, District of Columbia
| | - Gail E Graham
- Department of Genetics, Children's Hospital of Eastern Ontario, Ottawa, Ontario, Canada
| | - David A Stevenson
- Division of Medical Genetics, Stanford University, Stanford, California
| | - Heather Hanson
- Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, Utah
| | - David H Viskochil
- Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, Utah
| | - Laura C Baker
- Division of Medical Genetics, A. I. duPont Hospital for Children, Wilmington, Delaware
| | - Bridget Russo
- Center for Applied Clinical Genomics, A. I. duPont Hospital for Children, Wilmington, Delaware
| | - Nick Gardner
- Center for Applied Clinical Genomics, A. I. duPont Hospital for Children, Wilmington, Delaware
| | - Deborah L Stabley
- Center for Applied Clinical Genomics, A. I. duPont Hospital for Children, Wilmington, Delaware
| | - Verena Kolbe
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Georg Rosenberger
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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15
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Maringer K, Saheb E, Bush J. Vesicular Trafficking Defects, Developmental Abnormalities, and Alterations in the Cellular Death Process Occur in Cell Lines that Over-Express Dictyostelium GTPase, Rab2, and Rab2 Mutants. BIOLOGY 2014; 3:514-35. [PMID: 25157910 PMCID: PMC4192625 DOI: 10.3390/biology3030514] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Revised: 07/29/2014] [Accepted: 08/13/2014] [Indexed: 01/10/2023]
Abstract
Small molecular weight GTPase Rab2 has been shown to be a resident of pre-Golgi intermediates and required for protein transport from the ER to the Golgi complex, however, the function of Rab2 in Dictyostelium has yet to be fully characterized. Using cell lines that over-express DdRab2, as well as cell lines over-expressing constitutively active (CA), and dominant negative (DN) forms of the GTPase, we report a functional role in vesicular transport specifically phagocytosis, and endocytosis. Furthermore, Rab2 like other GTPases cycles between an active GTP-bound and an inactive GDP-bound state. We found that this GTP/GDP cycle for DdRab2 is crucial for normal Dictyostelium development and cell-cell adhesion. Similar to Rab5 and Rab7 in C. elegans, we found that DdRab2 plays a role in programmed cell death, possibly in the phagocytic removal of apoptotic corpses.
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Affiliation(s)
- Katherine Maringer
- Department of Biology, University of Arkansas at Little Rock, 2801 S. University Ave., Little Rock, AR 72205, USA.
| | - Entsar Saheb
- Department of Biology, University of Arkansas at Little Rock, 2801 S. University Ave., Little Rock, AR 72205, USA.
| | - John Bush
- Department of Biology, University of Arkansas at Little Rock, 2801 S. University Ave., Little Rock, AR 72205, USA.
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16
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K-Ras(G12C) inhibitors allosterically control GTP affinity and effector interactions. Nature 2013; 503:548-51. [PMID: 24256730 PMCID: PMC4274051 DOI: 10.1038/nature12796] [Citation(s) in RCA: 1582] [Impact Index Per Article: 143.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Accepted: 10/25/2013] [Indexed: 12/16/2022]
Abstract
Somatic mutations in the small GTPase K-Ras are the most common activating lesions found in human cancer, and are generally associated with poor response to standard therapies. Efforts to target this oncogene directly have faced difficulties owing to its picomolar affinity for GTP/GDP and the absence of known allosteric regulatory sites. Oncogenic mutations result in functional activation of Ras family proteins by impairing GTP hydrolysis. With diminished regulation by GTPase activity, the nucleotide state of Ras becomes more dependent on relative nucleotide affinity and concentration. This gives GTP an advantage over GDP and increases the proportion of active GTP-bound Ras. Here we report the development of small molecules that irreversibly bind to a common oncogenic mutant, K-Ras(G12C). These compounds rely on the mutant cysteine for binding and therefore do not affect the wild-type protein. Crystallographic studies reveal the formation of a new pocket that is not apparent in previous structures of Ras, beneath the effector binding switch-II region. Binding of these inhibitors to K-Ras(G12C) disrupts both switch-I and switch-II, subverting the native nucleotide preference to favour GDP over GTP and impairing binding to Raf. Our data provide structure-based validation of a new allosteric regulatory site on Ras that is targetable in a mutant-specific manner.
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17
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Bátor J, Varga J, Szeberényi J. The effect of sodium nitroprusside on survival and stress signaling in PC12 rat phaeochromocytoma cells expressing a dominant negative RasH mutant protein. Biochem Cell Biol 2013; 91:230-5. [PMID: 23859017 DOI: 10.1139/bcb-2012-0078] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Toxic concentrations of the second messenger nitric oxide cause cellular stress leading to cell death. Ras proteins, possible targets of nitric oxide-induced nitrosylation, may act as mediators in nitrosative stress. To analyze the possible involvement of Ras proteins in nitric oxide cytotoxicity, a PC12 rat phaeochromocytoma cell line expressing a dominant negative Ras mutant protein was used in this study. Cytotoxic concentrations of the nitric oxide donor sodium nitroprusside activated several proapoptotic mechanisms, including stimulation of the stress kinase pathways mediated by c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), inhibition of the translation initiation factor eIF2α, induction and phosphorylation of the p53 protein, and inhibited Akt-mediated antiapoptotic signaling, independent of Ras function. Simultaneously, Ras-dependent stimulation of the prosurvival ERK pathway was also observed, followed by an increased activation of the caspase-9/caspase-3 cascade in cells with impaired Ras function. It is concluded that nitric oxide stimulation of multiple signaling pathways contributes to the cell death program, whereas concomitant activation of the Ras/ERK pathway provides a certain degree of protection.
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Affiliation(s)
- Judit Bátor
- Department of Medical Biology, Medical School, University of Pécs, Pécs, Hungary
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18
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Lorenz S, Lissewski C, Simsek-Kiper PO, Alanay Y, Boduroglu K, Zenker M, Rosenberger G. Functional analysis of a duplication (p.E63_D69dup) in the switch II region of HRAS: new aspects of the molecular pathogenesis underlying Costello syndrome. Hum Mol Genet 2013; 22:1643-53. [PMID: 23335589 DOI: 10.1093/hmg/ddt014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Costello syndrome is a congenital disorder comprising a characteristic face, severe feeding difficulties, skeletal, cardiac and skin abnormalities, intellectual disability and predisposition to malignancies. It is caused by heterozygous germline HRAS mutations mostly affecting Gly(12) or Gly(13), which impair HRAS-GTPase activity and result in increased downstream signal flow independent of incoming signals. Functional analyses of rarer HRAS mutations identified in individuals with attenuated Costello syndrome phenotypes revealed altered GDP/GTP nucleotide affinities (p.K117R) and inefficient effector binding (p.E37dup). Thus, both phenotypic and functional variability associated with HRAS mutations are evident. Here, we report on a novel heterozygous HRAS germline mutation (c.187_207dup, p.E63_D69dup) in a girl presenting with a phenotype at the milder end of the Costello syndrome spectrum. The p.E63_D69dup mutation impaired co-precipitation of recombinant HRAS with NF1 GTPase-activating protein (GAP) suggesting constitutive HRAS(E63_D69dup) activation due to GAP insensitivity. Indeed, we identified strongly augmented active HRAS(E63_D69dup) that co-precipitated with effectors RAF1, RAL guanine nucleotide dissociation stimulator and phospholipase C1. However, we could not pull down active HRAS(E63_D69dup) using the target protein PIK3CA, indicating a compromised association between active HRAS(E63_D69dup) and PIK3CA. Accordingly, overexpression of HRAS(E63_D69dup) increased steady-state phosphorylation of MEK1/2 and ERK1/2 downstream of RAF, whereas AKT phosphorylation downstream of phosphoinositide 3-kinase (PI3K) was not enhanced. By analyzing signaling dynamics, we found that HRAS(E63_D69dup) has impaired reagibility to stimuli resulting in reduced and disrupted capacity to transduce incoming signals to the RAF-MAPK and PI3K-AKT cascade, respectively. We suggest that disrupted HRAS reagibility, as we demonstrate for the p.E63_D69dup mutation, is a previously unappreciated molecular pathomechanism underlying Costello syndrome.
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Affiliation(s)
- Sybille Lorenz
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany
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19
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Qi X, Zheng H. Functional analysis of small Rab GTPases in cytokinesis in Arabidopsis thaliana. Methods Mol Biol 2013; 1043:103-12. [PMID: 23913040 DOI: 10.1007/978-1-62703-532-3_11] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Rab proteins are key regulators of membrane transport in eukaryotes. Recent evidence from different species supports the notion that some Rab proteins are crucial for cytokinesis, a pivotal procedure for successful cell division. As a family of monomeric small GTPases of the Ras superfamily, the function of Rab proteins is modulated by guanine nucleotide binding and hydrolysis. To investigate the function of Rab proteins, creating dominant negative or constitutively active mutant forms of a Rab protein is a widely used approach. To study cytokinesis in plant cells, using fluorescent dye to highlight the cell shape and the nuclei, and to monitor the formation of the newly formed cell plate in mitotic cells, is easy and useful. In this chapter, we describe detailed methods for (1) generating transgenic plants expressing dominant negative or constitutively active form of RAB-A1c; (2) fluorescent staining of cell shape, cell wall, and nuclei of mitotic root tip cells; (3) fluorescent staining of newly formed cell plate; and (4) detecting fluorescent signals using Confocal Laser Scanning Microscopy in the genetic model plant species Arabidopsis thaliana.
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Affiliation(s)
- Xingyun Qi
- Department of Biology, McGill University, Montreal, QC, Canada
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20
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Gallegos ME, Balakrishnan S, Chandramouli P, Arora S, Azameera A, Babushekar A, Bargoma E, Bokhari A, Chava SK, Das P, Desai M, Decena D, Saramma SDD, Dey B, Doss AL, Gor N, Gudiputi L, Guo C, Hande S, Jensen M, Jones S, Jones N, Jorgens D, Karamchedu P, Kamrani K, Kolora LD, Kristensen L, Kwan K, Lau H, Maharaj P, Mander N, Mangipudi K, Menakuru H, Mody V, Mohanty S, Mukkamala S, Mundra SA, Nagaraju S, Narayanaswamy R, Ndungu-Case C, Noorbakhsh M, Patel J, Patel P, Pendem SV, Ponakala A, Rath M, Robles MC, Rokkam D, Roth C, Sasidharan P, Shah S, Tandon S, Suprai J, Truong TQN, Uthayaruban R, Varma A, Ved U, Wang Z, Yu Z. The C. elegans rab family: identification, classification and toolkit construction. PLoS One 2012; 7:e49387. [PMID: 23185324 PMCID: PMC3504004 DOI: 10.1371/journal.pone.0049387] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Accepted: 10/09/2012] [Indexed: 11/29/2022] Open
Abstract
Rab monomeric GTPases regulate specific aspects of vesicle transport in eukaryotes including coat recruitment, uncoating, fission, motility, target selection and fusion. Moreover, individual Rab proteins function at specific sites within the cell, for example the ER, golgi and early endosome. Importantly, the localization and function of individual Rab subfamily members are often conserved underscoring the significant contributions that model organisms such as Caenorhabditis elegans can make towards a better understanding of human disease caused by Rab and vesicle trafficking malfunction. With this in mind, a bioinformatics approach was first taken to identify and classify the complete C. elegans Rab family placing individual Rabs into specific subfamilies based on molecular phylogenetics. For genes that were difficult to classify by sequence similarity alone, we did a comparative analysis of intron position among specific subfamilies from yeast to humans. This two-pronged approach allowed the classification of 30 out of 31 C. elegans Rab proteins identified here including Rab31/Rab50, a likely member of the last eukaryotic common ancestor (LECA). Second, a molecular toolset was created to facilitate research on biological processes that involve Rab proteins. Specifically, we used Gateway-compatible C. elegans ORFeome clones as starting material to create 44 full-length, sequence-verified, dominant-negative (DN) and constitutive active (CA) rab open reading frames (ORFs). Development of this toolset provided independent research projects for students enrolled in a research-based molecular techniques course at California State University, East Bay (CSUEB).
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Affiliation(s)
- Maria E Gallegos
- Department of Biological Sciences, California State University East Bay, Hayward, CA, USA.
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21
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Gripp KW, Bifeld E, Stabley DL, Hopkins E, Meien S, Vinette K, Sol-Church K, Rosenberger G. A novel HRAS substitution (c.266C>G; p.S89C) resulting in decreased downstream signaling suggests a new dimension of RAS pathway dysregulation in human development. Am J Med Genet A 2012; 158A:2106-18. [PMID: 22821884 DOI: 10.1002/ajmg.a.35449] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Accepted: 04/08/2012] [Indexed: 12/13/2022]
Abstract
Costello syndrome is caused by HRAS germline mutations affecting Gly(12) or Gly(13) in >90% of cases and these are associated with a relatively homogeneous phenotype. Rarer mutations in other HRAS codons were reported in patients with an attenuated or mild phenotype. Disease-associated HRAS missense mutations result in constitutive HRAS activation and increased RAF-MEK-ERK and PI3K-AKT signal flow. Here we report on a novel heterozygous HRAS germline alteration, c.266C>G (p.S89C), in a girl presenting with severe fetal hydrops and pleural effusion, followed by a more benign postnatal course. A sibling with the same mutation and fetal polyhydramnios showed a Dandy-Walker malformation; his postnatal course was complicated by severe feeding difficulties. Their apparently asymptomatic father is heterozygous for the c.266C>G change. By functional analyses we identified reduced levels of active HRAS(S89C) and diminished MEK, ERK and AKT phosphorylation in cells overexpressing HRAS(S89C) , which represent novel consequences of disease-associated HRAS mutations. Given our patients' difficult neonatal course and presence of this change in their asymptomatic father, we hypothesize that its harmful consequences may be time limited, with the late fetal stage being most sensitive. Alternatively, the phenotype may develop only in the presence of an additional as-yet-unknown genetic modifier. While the pathogenicity of the HRAS c.266C>G change remains unproven, our data may illustrate wide functional and phenotypic variability of germline HRAS mutations.
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Affiliation(s)
- Karen W Gripp
- Division of Medical Genetics, A. I. duPont Hospital for Children, Wilmington, Delaware, USA
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Hu YH, Deng T, Sun L. The Rab1 GTPase of Sciaenops ocellatus modulates intracellular bacterial infection. FISH & SHELLFISH IMMUNOLOGY 2011; 31:1005-1012. [PMID: 21889593 DOI: 10.1016/j.fsi.2011.08.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2011] [Revised: 08/21/2011] [Accepted: 08/22/2011] [Indexed: 05/31/2023]
Abstract
The Rab family proteins belong to the Ras-like GTPase superfamily and play important roles in intracellular membrane trafficking. To date no studies on fish Rab have been documented, though rab-like sequences have been found in a number of teleosts. In this study, we identified and analyzed a Rab homologue, SoRab1, from red drum, Sciaenops ocellatus. The cDNA of SoRab1 contains a 5'- untranslated region (UTR) of 358 bp, an open reading frame (ORF) of 612 bp, and a 3'-UTR of 265 bp. The ORF encodes a putative protein of 203 residues, which shares 92-99% overall sequence identities with the Rab1 from fish, human, and mouse. SoRab1 possesses a typical Rab1 GTPase domain with the conserved G box motifs and the switch I and switch II regions. Recombinant SoRab1 purified from Escherichia coli exhibits apparent GTPase activity. Quantitative real time RT-PCR analysis showed that SoRab1 expression was detected in a number of tissues, with the lowest expression found in blood and highest expression found in muscle. Bacterial and lipopolysaccharide challenges significantly upregulated SoRab1 expression in liver, kidney, and spleen in time-dependent manners. Transient overexpression of SoRab1 in primary hepatocytes reduced intracellular bacterial infection, whereas interference with SoRab1 expression by RNAi enhanced intracellular bacterial invasion. These results provide the first indication that a fish Rab1 GTPase, SoRab1, regulates intracellular bacterial infection and thus is likely to play a role in bacteria-induced host immune defense.
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Affiliation(s)
- Yong-hua Hu
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, PR China
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23
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Löcke S, Fricke I, Mucha E, Humpert ML, Berken A. Interactions in the pollen-specific receptor-like kinases-containing signaling network. Eur J Cell Biol 2010; 89:917-23. [DOI: 10.1016/j.ejcb.2010.08.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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Effects of site-directed mutagenesis of mglA on motility and swarming of Myxococcus xanthus. BMC Microbiol 2010; 10:295. [PMID: 21083931 PMCID: PMC3000849 DOI: 10.1186/1471-2180-10-295] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Accepted: 11/18/2010] [Indexed: 01/31/2023] Open
Abstract
Background The mglA gene from the bacterium Myxococcus xanthus encodes a 22kDa protein related to the Ras superfamily of monomeric GTPases. MglA is required for the normal function of A-motility (adventurous), S-motility (social), fruiting body morphogenesis, and sporulation. MglA and its homologs differ from all eukaryotic and other prokaryotic GTPases because they have a threonine (Thr78) in place of the highly conserved aspartate residue of the consensus PM3 (phosphate-magnesium binding) region. To identify residues critical for MglA function or potential protein interactions, and explore the function of Thr78, the phenotypes of 18 mglA mutants were characterized. Results Nine mutants, with mutations predicted to alter residues that bind the guanine base or coordinate magnesium, did not produce detectable MglA. As expected, these mutants were mot- dev- because MglA is essential for these processes. Of the remaining nine mutants, seven showed a wild-type distribution pattern for MglA but fell into two categories with regard to function. Five of the seven mutants exhibited mild phenotypes, but two mutants, T78D and P80A, abolished motility and development. The localization pattern of MglA was abolished in two mutants that were mot- spo- and dev-. These two mutants were predicted to alter surface residues at Asp52 and Thr54, which suggests that these residues are critical for proper localization and may define a protein interaction site. Improving the consensus match with Ras at Thr78 abolished function of MglA. Only the conservative serine substitution was tolerated at this position. Merodiploid constructs revealed that a subset of alleles, including mglAD52A, were dominant and also illustrated that changing the balance of MglA and its co-transcribed partner, MglB, affects A-motility. Conclusion Our results suggest that GTP binding is critical for stability of MglA because MglA does not accumulate in mutants that cannot bind GTP. The threonine in PM3 of MglA proteins represents a novel modification of the highly conserved GTPase consensus at this position. The requirement for a hydroxyl group at this position may indicate that MglA is subject to modification under certain conditions. Proper localization of MglA is critical for both motility and development and likely involves protein interactions mediated by residues Asp52 and Thr54.
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Berg TJ, Gastonguay AJ, Lorimer EL, Kuhnmuench JR, Li R, Fields AP, Williams CL. Splice variants of SmgGDS control small GTPase prenylation and membrane localization. J Biol Chem 2010; 285:35255-66. [PMID: 20709748 PMCID: PMC2975149 DOI: 10.1074/jbc.m110.129916] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ras and Rho small GTPases possessing a C-terminal polybasic region (PBR) are vital signaling proteins whose misregulation can lead to cancer. Signaling by these proteins depends on their ability to bind guanine nucleotides and their prenylation with a geranylgeranyl or farnesyl isoprenoid moiety and subsequent trafficking to cellular membranes. There is little previous evidence that cellular signals can restrain nonprenylated GTPases from entering the prenylation pathway, leading to the general belief that PBR-possessing GTPases are prenylated as soon as they are synthesized. Here, we present evidence that challenges this belief. We demonstrate that insertion of the dominant negative mutation to inhibit GDP/GTP exchange diminishes prenylation of Rap1A and RhoA, enhances prenylation of Rac1, and does not detectably alter prenylation of K-Ras. Our results indicate that the entrance and passage of these small GTPases through the prenylation pathway is regulated by two splice variants of SmgGDS, a protein that has been reported to promote GDP/GTP exchange by PBR-possessing GTPases and to be up-regulated in several forms of cancer. We show that the previously characterized 558-residue SmgGDS splice variant (SmgGDS-558) selectively associates with prenylated small GTPases and facilitates trafficking of Rap1A to the plasma membrane, whereas the less well characterized 607-residue SmgGDS splice variant (SmgGDS-607) associates with nonprenylated GTPases and regulates the entry of Rap1A, RhoA, and Rac1 into the prenylation pathway. These results indicate that guanine nucleotide exchange and interactions with SmgGDS splice variants can regulate the entrance and passage of PBR-possessing small GTPases through the prenylation pathway.
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Affiliation(s)
- Tracy J Berg
- Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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Aronsson H, Combe J, Patel R, Agne B, Martin M, Kessler F, Jarvis P. Nucleotide binding and dimerization at the chloroplast pre-protein import receptor, atToc33, are not essential in vivo but do increase import efficiency. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2010; 63:297-311. [PMID: 20444229 DOI: 10.1111/j.1365-313x.2010.04242.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The atToc33 protein is one of several pre-protein import receptors in the outer envelope of Arabidopsis chloroplasts. It is a GTPase with motifs characteristic of such proteins, and its loss in the plastid protein import 1 (ppi1) mutant interferes with the import of photosynthesis-related pre-proteins, causing a chlorotic phenotype in mutant plants. To assess the significance of GTPase cycling by atToc33, we generated several atToc33 point mutants with predicted effects on GTP binding (K49R, S50N and S50N/S51N), GTP hydrolysis (G45R, G45V, Q68A and N101A), both binding and hydrolysis (G45R/K49N/S50R), and dimerization or the functional interaction between dimeric partners (R125A, R130A and R130K). First, a selection of these mutants was assessed in vitro, or in yeast, to confirm that the mutations have the desired effects: in relation to nucleotide binding and dimerization, the mutants behaved as expected. Then, activities of selected mutants were tested in vivo, by assessing for complementation of ppi1 in transgenic plants. Remarkably, all tested mutants mediated high levels of complementation: complemented plants were similar to the wild type in growth rate, chlorophyll accumulation, photosynthetic performance, and chloroplast ultrastructure. Protein import into mutant chloroplasts was also complemented to >50% of the wild-type level. Overall, the data indicate that neither nucleotide binding nor dimerization at atToc33 is essential for chloroplast import (in plants that continue to express the other TOC receptors in native form), although both processes do increase import efficiency. Absence of atToc33 GTPase activity might somehow be compensated for by that of the Toc159 receptors. However, overexpression of atToc33 (or its close relative, atToc34) in Toc159-deficient plants did not mediate complementation, indicating that the receptors do not share functional redundancy in the conventional sense.
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Affiliation(s)
- Henrik Aronsson
- Department of Plant and Environmental Sciences, University of Gothenburg, Box 461, SE-405 30 Gothenburg, Sweden
| | - Jonathan Combe
- Department of Biology, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Ramesh Patel
- Department of Biology, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - Birgit Agne
- Laboratoire de Physiologie Végétale, Université de Neuchâtel, Rue Emile-Argand 11, 2007 Neuchâtel, Switzerland
| | - Meryll Martin
- Laboratoire de Physiologie Végétale, Université de Neuchâtel, Rue Emile-Argand 11, 2007 Neuchâtel, Switzerland
| | - Felix Kessler
- Laboratoire de Physiologie Végétale, Université de Neuchâtel, Rue Emile-Argand 11, 2007 Neuchâtel, Switzerland
| | - Paul Jarvis
- Department of Biology, University of Leicester, University Road, Leicester LE1 7RH, UK
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Gremer L, De Luca A, Merbitz-Zahradnik T, Dallapiccola B, Morlot S, Tartaglia M, Kutsche K, Ahmadian MR, Rosenberger G. Duplication of Glu37 in the switch I region of HRAS impairs effector/GAP binding and underlies Costello syndrome by promoting enhanced growth factor-dependent MAPK and AKT activation. Hum Mol Genet 2009; 19:790-802. [DOI: 10.1093/hmg/ddp548] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
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28
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Rosenberger G, Meien S, Kutsche K. Oncogenic HRAS mutations cause prolonged PI3K signaling in response to epidermal growth factor in fibroblasts of patients with Costello syndrome. Hum Mutat 2009; 30:352-62. [PMID: 19035362 DOI: 10.1002/humu.20855] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Costello syndrome (CS) is a rare congenital disorder characterized by failure to thrive, craniofacial dysmorphisms, cardiac and skin abnormalities, mental retardation, and predisposition to malignancies. CS is caused by heterozygous gain-of-function mutations in HRAS that also occur as somatic alterations in human tumors. HRAS is one of the three classical RAS proteins and cycles between an active, GTP- and an inactive, GDP-bound conformation. We used primary human skin fibroblasts from patients with CS as a model system to study the functional consequences of HRAS mutations on endogenous signaling pathways. The GTP-bound form of HRAS was significantly enriched in CS compared with normal fibroblasts. Active HRAS is known to stimulate both the RAF-MEK-ERK and the PI3K-AKT signaling cascade. Phosphorylation of MEK and ERK was normal in CS fibroblasts under basal conditions and slightly prolonged after epidermal growth factor (EGF) stimulation. Interestingly, basal phosphorylation of AKT was increased yet more in CS fibroblasts. Moreover, AKT phosphorylation was diminished in the early and enhanced in the late phase of EGF stimulation. Taken together, these results document that CS-associated HRAS mutations result in prolonged signal flux in a ligand-dependent manner. Our data suggest that altered cellular response to growth factors rather than constitutive activation of HRAS downstream signaling molecules may contribute to some of the clinical features in patients with CS.
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Affiliation(s)
- Georg Rosenberger
- Institut für Humangenetik, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany
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29
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Lee MTG, Mishra A, Lambright DG. Structural mechanisms for regulation of membrane traffic by rab GTPases. Traffic 2009; 10:1377-89. [PMID: 19522756 DOI: 10.1111/j.1600-0854.2009.00942.x] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In all eukaryotic organisms, Rab GTPases function as critical regulators of membrane traffic, organelle biogenesis and maturation, and related cellular processes. The numerous Rab proteins have distinctive yet overlapping subcellular distributions throughout the endomembrane system. Intensive investigation has clarified the underlying molecular and structural mechanisms for several ubiquitous Rab proteins that control membrane traffic between tubular-vesicular organelles in the exocytic, endocytic and recycling pathways. In this review, we focus on structural insights that inform our current understanding of the organization of the Rab family as well as the mechanisms for membrane targeting and activation, interaction with effectors, deactivation and specificity determination.
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Affiliation(s)
- Meng-Tse Gabe Lee
- Program in Molecular Medicine and Department of Biochemistry & Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA
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30
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Foucart C, Jauneau A, Gion JM, Amelot N, Martinez Y, Panegos P, Grima-Pettenati J, Sivadon P. Overexpression of EgROP1, a Eucalyptus vascular-expressed Rac-like small GTPase, affects secondary xylem formation in Arabidopsis thaliana. THE NEW PHYTOLOGIST 2009; 183:1014-1029. [PMID: 19549133 DOI: 10.1111/j.1469-8137.2009.02910.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
To better understand the genetic control of secondary xylem formation in trees we analysed genes expressed during Eucalyptus xylem development. Using eucalyptus xylem cDNA libraries, we identified EgROP1, a member of the plant ROP family of Rho-like GTPases. These signalling proteins are central regulators of many important processes in plants, but information on their role in xylogenesis is scarce. Quantitative real-time reverse-transcriptase polymerase chain reaction (qRT-PCR) confirmed that EgROP1 was preferentially expressed in the cambial zone and differentiating xylem in eucalyptus. Genetic mapping performed in a eucalyptus breeding population established a link between EgROP1 sequence polymorphisms and quantitative trait loci (QTLs) related to lignin profiles and fibre morphology. Overexpression of various forms of EgROP1 in Arabidopsis thaliana altered anisotropic cell growth in transgenic leaves, but most importantly affected vessel element and fibre growth in secondary xylem. Patches of fibre-like cells in the secondary xylem of transgenic plants showed changes in secondary cell wall thickness, lignin and xylan composition. These results suggest a role for EgROP1 in fibre cell morphology and secondary cell wall formation making it a good candidate gene for marker-based selection of eucalyptus trees.
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Affiliation(s)
- Camille Foucart
- UMR 5546 CNRS/Université Toulouse III, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 42617 Auzeville, F-31326 Castanet Tolosan, France
| | - Alain Jauneau
- IFR 40, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 42617 Auzeville, F-31326 Castanet Tolosan, France
| | - Jean-Marc Gion
- UPR39 Génétique Forestière, Cirad-BIOS, Campus de Baillarguet TA 10C, F-34398 Montpellier Cedex 5, France
| | - Nicolas Amelot
- UMR 5546 CNRS/Université Toulouse III, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 42617 Auzeville, F-31326 Castanet Tolosan, France
| | - Yves Martinez
- IFR 40, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 42617 Auzeville, F-31326 Castanet Tolosan, France
| | - Patricia Panegos
- UMR 5546 CNRS/Université Toulouse III, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 42617 Auzeville, F-31326 Castanet Tolosan, France
| | - Jacqueline Grima-Pettenati
- UMR 5546 CNRS/Université Toulouse III, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 42617 Auzeville, F-31326 Castanet Tolosan, France
| | - Pierre Sivadon
- UMR 5546 CNRS/Université Toulouse III, Pôle de Biotechnologies Végétales, 24 chemin de Borde Rouge, BP 42617 Auzeville, F-31326 Castanet Tolosan, France
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Soundararajan M, Turnbull A, Fedorov O, Johansson C, Doyle DA. RhoB can adopt a Mg2+ free conformation prior to GEF binding. Proteins 2008; 72:498-505. [PMID: 18393397 DOI: 10.1002/prot.22017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Meera Soundararajan
- Structural Genomics Consortium, University of Oxford, Old Road Campus Research Building, Old Road Campus, off Roosevelt Drive, Headington OX3 7DQ, United Kingdom
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32
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Veltel S, Kravchenko A, Ismail S, Wittinghofer A. Specificity of Arl2/Arl3 signaling is mediated by a ternary Arl3-effector-GAP complex. FEBS Lett 2008; 582:2501-7. [PMID: 18588884 DOI: 10.1016/j.febslet.2008.05.053] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 05/09/2008] [Accepted: 05/13/2008] [Indexed: 10/21/2022]
Abstract
Arl2 and Arl3, members of the Arf subfamily of small G proteins, are believed to be involved in ciliary and microtubule-dependent processes. Recently, we could identify RP2, responsible for a variant of X-linked retinitis pigmentosa, as the Arl3-specific GAP. Here, we have characterized Arl2/3 interactions. We show the formation of a ternary complex between Arl3, its cognate GAP RP2 and its retinal effector HRG4. This complex seems to be important for photoreceptor function.
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Affiliation(s)
- Stefan Veltel
- Max-Planck-Institut für molekulare Physiologie, Abteilung Strukturelle Biologie, Otto-Hahn-Strasse 11, Dortmund, Germany
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Vallee RB, Herskovits JS, Aghajanian JG, Burgess CC, Shpetner HS. Dynamin, a GTPase involved in the initial stages of endocytosis. CIBA FOUNDATION SYMPOSIUM 2007; 176:185-93; discussion 193-7. [PMID: 8299419 DOI: 10.1002/9780470514450.ch12] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Dynamin is a high molecular mass (100 kDa) GTPase which binds to and co-purifies with microtubules. Molecular cloning of rat brain dynamin has revealed the three well-established consensus sequence elements for GTP binding within the N-terminal third of the protein, as well as sequence similarity within this region to the interferon-inducible antiviral Mx proteins, the product of the yeast membrane sorting gene VPS1, and the product of the yeast mitochondrial replication gene MGM1. More extensive sequence similarity between rat dynamin and the product of the Drosophila gene shibire, which is involved in endocytosis, has also been found. In in vitro assays microtubules strongly stimulate the dynamin GTPase. This effect can be reversed by removal of the dynamin C-terminus using papain, which abolishes microtubule binding. Overexpression of mutant forms of dynamin in vivo using Cos-7 cells inhibits transferrin uptake and alters the distribution of clathrin and of alpha-adaptin, but not gamma-adaptin. Deletion of the C-terminus of mutant forms of dynamin abolishes these effects. Together these results suggest a critical role for dynamin in the early stages of endocytosis. It is uncertain whether microtubules interact with dynamin in vivo or whether the in vitro effects of microtubules mimic the effects of other regulatory elements in vivo.
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Affiliation(s)
- R B Vallee
- Cell Biology Group, Worcester Foundation for Experimental Biology, Shrewsbury, MA
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Yang S, Farias M, Kapfhamer D, Tobias J, Grant G, Abel T, Bućan M. Biochemical, molecular and behavioral phenotypes of Rab3A mutations in the mouse. GENES, BRAIN, AND BEHAVIOR 2007; 6:77-96. [PMID: 16734774 PMCID: PMC2914309 DOI: 10.1111/j.1601-183x.2006.00235.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ras-associated binding (Rab) protein 3A is a neuronal guanosine triphosphate (GTP)-binding protein that binds synaptic vesicles and regulates synaptic transmission. A mouse mutant, earlybird (Ebd), with a point mutation in the GTP-binding domain of Rab3A (D77G), exhibits anomalies in circadian behavior and homeostatic response to sleep loss. Here, we show that the D77G substitution in the Ebd allele causes reduced GTP and GDP binding, whereas GTPase activity remains intact, leading to reduced protein levels of both Rab3A and rabphilin3A. Expression profiling of the cortex and hippocampus of Ebd and Rab3a-deficient mice revealed subtle differences between wild-type and mutant mice. Although mice were backcrossed for three generations to a C57BL/6J background, the most robust changes at the transcriptional level between Rab3a(-/-) and Rab3a(+/+) mice were represented by genes from the 129/Sv-derived chromosomal region surrounding the Rab3a gene. These results showed that differences in genetic background have a stronger effect on gene expression than the mutations in the Rab3a gene. In behavioral tests, the Ebd/Ebd mice showed a more pronounced mutant phenotype than the null mice; Ebd/Ebd have reduced anxiety-like behavior in the elevated zero-maze test, reduced response to stress in the forced swim test and a deficit in cued fear conditioning (FC), whereas Rab3a(-/-) showed only a deficit in cued FC. Our data implicate Rab3A in learning and memory as well as in the regulation of emotion. A combination of forward and reverse genetics has provided multiple alleles of the Rab3a gene; our studies illustrate the power and complexities of the parallel analysis of these alleles at the biochemical, molecular and behavioral levels.
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Affiliation(s)
- S. Yang
- Department of Genetics, University of Pennsylvania, Philadelphia, PA
| | - M. Farias
- Department of Genetics, University of Pennsylvania, Philadelphia, PA
| | - D. Kapfhamer
- Department of Genetics, University of Pennsylvania, Philadelphia, PA
| | - J. Tobias
- Penn Center for Bioinformatics, University of Pennsylvania, Philadelphia, PA, USA
| | - G. Grant
- Department of Genetics, University of Pennsylvania, Philadelphia, PA
- Penn Center for Bioinformatics, University of Pennsylvania, Philadelphia, PA, USA
| | - T. Abel
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
| | - M. Bućan
- Department of Genetics, University of Pennsylvania, Philadelphia, PA
- Penn Center for Bioinformatics, University of Pennsylvania, Philadelphia, PA, USA
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Blangy A, Bouquier N, Gauthier-Rouvière C, Schmidt S, Debant A, Leonetti JP, Fort P. Identification of TRIO-GEFD1 chemical inhibitors using the yeast exchange assay. Biol Cell 2006; 98:511-22. [PMID: 16686599 DOI: 10.1042/bc20060023] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
BACKGROUND INFORMATION Rho GTPases are involved in many biological processes and participate in cancer development. Their activation is catalysed by exchange factors [RhoGEFs (Rho GTPase guanine nucleotide-exchange factor)] of the Dbl family. RhoGEFs display proto-oncogenic features, thus appearing as candidate targets for anticancer drugs. Dominant-negative Rho GTPase mutants have been widely used to block RhoGEF signalling. However, these tools suffer from limitations, due to the high number of RhoGEFs and the complex mechanisms that control Rho GTPase activation. RESULTS RhoG-T17N is a poor inhibitor of its exchange factor TRIO-GEFD1 (first exchange domain of the exchange factor TRIO) in vivo: although it binds to TRIO-GEFD1, RhoG-T17N does not block the downstream signalling. Using the yeast exchange assay, we show that in the presence of TRIO-GEFD1, RhoG-T17N can bind to its effectors, which illustrates how negative mutants may produce misleading interpretations and emphasizes the need for new types of RhoGEF inhibitors. In that prospect, we adapted the yeast exchange assay method to identify RhoGEF inhibitors. Using this novel approach, we screened a 3500-chemical-compound library and identified a potential inhibitor of TRIO-GEFD1. This molecule inhibited TRIO-GEFD1 in vitro. Among the chemical analogues of this compound, we identified two molecules with better inhibitory activity. The three TRIO-GEFD1 inhibitors had no effect on ARHGEF17 and ARNO [ARF (ADP-ribosylation factor) nucleotide-binding-site opener], two exchange factors for RhoA and Arf1 respectively. CONCLUSIONS The development of RhoGEF inhibitors appears as a valuable tool for the study of Rho GTPase signalling pathways. The yeast exchange assay adaptation we present here is suitable to screen for chemical or peptide libraries and identify candidate inhibitors.
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Affiliation(s)
- Anne Blangy
- Centre de Recherches en Biochimie Macromoléculaire, CNRS (Centre National de la Recherche Scientifique) FRE2593, 1919 route de Mende, 34293 Montpellier Cedex 5, France.
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Lommerse PHM, Snaar-Jagalska BE, Spaink HP, Schmidt T. Single-molecule diffusion measurements of H-Ras at the plasma membrane of live cells reveal microdomain localization upon activation. J Cell Sci 2005; 118:1799-809. [PMID: 15860728 DOI: 10.1242/jcs.02300] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Recent studies show that the partitioning of the small GTPase H-Ras in different types of membrane microdomains is dependent on guanosine 5'-triphosphate (GTP)-loading of H-Ras. Detailed knowledge about the in vivo dynamics of this phenomenon is limited. In this report, the effect of the activation of H-Ras on its microdomain localization was studied by single-molecule fluorescence microscopy. Individual human H-Ras molecules fused to the enhanced yellow fluorescent protein (eYFP) were imaged in the dorsal plasma membrane of live mouse cells and their diffusion behavior was analyzed. The diffusion of a constitutively inactive (S17N) and constitutively active (G12V) mutant of H-Ras was compared. Detailed analysis revealed that for both mutants a major, fast-diffusing population and a minor, slow-diffusing population were present. The slow-diffusing fraction of the active mutant was confined to 200 nm domains, which were not observed for the inactive mutant. In line with these results we observed that the slow-diffusing fraction of wild-type H-Ras became confined to 200 nm domains upon insulin-induced activation of wild-type H-Ras. This activation-dependent localization of H-Ras to 200 nm domains, for the first time directly detected in live cells, supports the proposed relationship between H-Ras microdomain localization and activation.
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Affiliation(s)
- Piet H M Lommerse
- Department of Biophysics, Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
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Datta K, Skidmore JM, Pu K, Maddock JR. The Caulobacter crescentus GTPase CgtAC is required for progression through the cell cycle and for maintaining 50S ribosomal subunit levels. Mol Microbiol 2005; 54:1379-92. [PMID: 15554976 DOI: 10.1111/j.1365-2958.2004.04354.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The Obg subfamily of bacterial GTP-binding proteins are biochemically distinct from Ras-like proteins raising the possibility that they are not controlled by conventional guanine nucleotide exchange factors (GEFs) and/or guanine nucleotide activating proteins (GAPs). To test this hypothesis, we generated mutations in the Caulobacter crescentus obg gene (cgtAC) which, in Ras-like proteins, would result in either activating or dominant negative phenotypes. In C. crescentus, a P168V mutant is not activating in vivo, although in vitro, the P168V protein showed a modest reduction in the affinity for GDP. Neither the S173N nor N280Y mutations resulted in a dominant negative phenotype. Furthermore, the S173N was significantly impaired for GTP binding, consistent with a critical role of this residue in GTP binding. In general, conserved amino acids in the GTP-binding pocket were, however, important for function. To examine the in vivo consequences of depleting CgtAC, we generated a temperature-sensitive mutant, G80E. At the permissive temperature, G80E cells grow slowly and have reduced levels of 50S ribosomal subunits, indicating that CgtAC is important for 50S assembly and/or stability. Surprisingly, at the non-permissive temperature, G80E cells rapidly lose viability and yet do not display an additional ribosome defect. Thus, the essential nature of the cgtAC gene does not appear to result from its ribosome function. G80E cells arrest as predivisional cells and stalkless cells. Flow cytometry on synchronized cells reveals a G1-S arrest. Therefore, CgtAC is necessary for DNA replication and progression through the cell cycle.
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Affiliation(s)
- Kaustuv Datta
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
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Moeder W, Yoshioka K, Klessig DF. Involvement of the small GTPase Rac in the defense responses of tobacco to pathogens. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2005; 18:116-24. [PMID: 15720080 DOI: 10.1094/mpmi-18-0116] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
During the hypersensitive response (HR), plants accumulate reactive oxygen species (ROS) that are likely generated at least in part by an NADPH oxidase similar to that found in mammalian neutrophils. An essential regulator of mammalian NADPH oxidase is the small GTP-binding protein Rac. To investigate whether Rac also regulates the pathogen-induced oxidative burst in plants, a dominant negative form of the rice OsRac1 gene was overexpressed in tobacco carrying the N resistance gene. Following infection with Tobacco mosaic virus (TMV), DN-OsRacl plants developed smaller lesions than wild-type plants, accumulated lower levels of lipid peroxidation products, and failed to activate expression of antioxidant genes. These results, combined with the demonstration that superoxide and hydrogen peroxide levels were reduced in DN-OsRacl tobacco developing a synchronous HR triggered by transient expression of the TMV p50 helicase domain or the Pto and AvrPto proteins, suggest that ROS production is impaired. The dominant negative effect of DN-OsRacl could be rescued by transiently overexpressing the wild-type OsRac1 protein. TMV-induced salicylic acid accumulation also was compromised in DN-OsRacl tobacco. Interestingly, while systemic acquired resistance to TMV was not impaired, nonhost resistance to Pseudomonas syringae pv. maculicola ES4326 was suppressed. Thus, the effect DN-OsRac1 expression exerts on the resistance signaling pathway appears to vary depending on the identity of the inoculated pathogen.
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Affiliation(s)
- Wolfgang Moeder
- Boyce Thompson Institute for Plant Research, Ithaca, NY 14850, USA
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39
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Cleator JH, Ravenell R, Kurtz DT, Hildebrandt JD. A dominant negative Galphas mutant that prevents thyroid-stimulating hormone receptor activation of cAMP production and inositol 1,4,5-trisphosphate turnover: competition by different G proteins for activation by a common receptor. J Biol Chem 2004; 279:36601-7. [PMID: 15234971 DOI: 10.1074/jbc.m406232200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A Ser to Asn mutation at position 54 of the alpha subunit of G(s) (designated N54-alpha(s)) was characterized after transient expression of it with various components of the receptor-adenylyl cyclase pathway in COS-1, COS-7, and HEK 293 cells. Previous studies of the N54-alpha(s) mutant revealed that it has a conditional dominant negative phenotype that prevents hormone-stimulated increases in cAMP without interfering with the regulation of basal cAMP levels (Cleator, J. H., Mehta, N. D., Kurtz, D. K., Hildebrandt, J. D. (1999) FEBS Lett. 243, 205-208). Experiments reported here were conducted to localize the mechanism of the dominant negative effect of the mutant. Competition studies conducted with activated alpha(s)* (Q212L) showed that the N54 mutant did not work down-stream by blocking the interaction of endogenous alpha(s) with adenylyl cyclase. The co-expression of wild type or N54-alpha(s) along with the thyroid-stimulating hormone (TSH) receptor and adenylyl cyclase isotypes differing with respect to betagamma stimulation (AC II or AC III) revealed that the phenotype of the mutant is not dependent upon the presence of adenylyl cyclase isoforms regulated by betagamma. These studies ruled out a downstream site of action of the mutant. To investigate an upstream site of action, N54-alpha(s) was co-expressed with either the TSH receptor that activates both alpha(s) and alpha(q) or with the alpha(1B)-adrenergic receptor that activates only alpha(q). N54-alpha(s) failed to inhibit alpha(1B)-adrenergic receptor stimulation of inositol 1,4,5-trisphosphate production but did inhibit TSH stimulation of inositol 1,4,5-trisphosphate. These results show that G(s) and G(q) compete for activation by the TSH receptor. They also indicate that the N54 protein has a dominant negative phenotype by blocking upstream receptor interactions with normal G proteins. This phenotype is different from that seen in analogous mutants of other G protein alpha subunits and suggests that either regulation or protein-protein interactions differ among G protein alpha subunits.
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Affiliation(s)
- John H Cleator
- Department of Pharmacology, Medical University of South Carolina, Charleston, SC 29425, USA
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Alto NM, Soderling J, Scott JD. Rab32 is an A-kinase anchoring protein and participates in mitochondrial dynamics. J Cell Biol 2002; 158:659-68. [PMID: 12186851 PMCID: PMC2174006 DOI: 10.1083/jcb.200204081] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
A-kinase anchoring proteins (AKAPs) tether the cAMP-dependent protein kinase (PKA) and other signaling enzymes to distinct subcellular organelles. Using the yeast two-hybrid approach, we demonstrate that Rab32, a member of the Ras superfamily of small molecular weight G-proteins, interacts directly with the type II regulatory subunit of PKA. Cellular and biochemical studies confirm that Rab32 functions as an AKAP inside cells. Anchoring determinants for PKA have been mapped to sites within the conserved alpha5 helix that is common to all Rab family members. Subcellular fractionation and immunofluorescent approaches indicate that Rab32 and a proportion of the cellular PKA pool are associated with mitochondria. Transient transfection of a GTP binding-deficient mutant of Rab32 promotes aberrant accumulation of mitochondria at the microtubule organizing center. Further analysis of this mutant indicates that disruption of the microtubule cytoskeleton results in aberrantly elongated mitochondria. This implicates Rab32 as a participant in synchronization of mitochondrial fission. Thus, Rab32 is a dual function protein that participates in both mitochondrial anchoring of PKA and mitochondrial dynamics.
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Affiliation(s)
- Neal M Alto
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health and Sciences University, 3181 SW Sam Jackson Park Road, Portland, OR 97201, USA
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41
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Ehrlich JS, Hansen MD, Nelson WJ. Spatio-temporal regulation of Rac1 localization and lamellipodia dynamics during epithelial cell-cell adhesion. Dev Cell 2002; 3:259-70. [PMID: 12194856 PMCID: PMC3369831 DOI: 10.1016/s1534-5807(02)00216-2] [Citation(s) in RCA: 279] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Cadherin-dependent epithelial cell-cell adhesion is thought to be regulated by Rho family small GTPases and PI 3-kinase, but the mechanisms involved are poorly understood. Using time-lapse microscopy and quantitative image analysis, we show that cell-cell contact in MDCK epithelial cells coincides with a spatio-temporal reorganization of plasma membrane Rac1 and lamellipodia from noncontacting to contacting surfaces. Within contacts, Rac1 and lamellipodia transiently concentrate at newest sites, but decrease at older, stabilized sites. Significantly, Rac1 mutants alter kinetics of cell-cell adhesion and strengthening, but not the eventual generation of cell-cell contacts. Products of PI 3-kinase activity also accumulate dynamically at contacts, but are not essential for either initiation or development of cell-cell adhesion. These results define a role for Rac1 in regulating the rates of initiation and strengthening of cell-cell adhesion.
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Tornero P, Chao RA, Luthin WN, Goff SA, Dangl JL. Large-scale structure-function analysis of the Arabidopsis RPM1 disease resistance protein. THE PLANT CELL 2002; 14:435-50. [PMID: 11884685 PMCID: PMC152923 DOI: 10.1105/tpc.010393] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2001] [Accepted: 10/29/2001] [Indexed: 05/17/2023]
Abstract
The Arabidopsis RPM1 gene confers resistance against Pseudomonas syringae expressing either the AvrRpm1 or the AvrB type III effector protein. We present an exhaustive genetic screen for mutants that no longer recognize avrRpm1. Using an inducible avrRpm1 expression system, we identified 110 independent mutations. These mutations represent six complementation groups. None discriminates between avrRpm1 and avrB recognition. We identified 95 rpm1 alleles and present a detailed structure--function analysis of the RPM1 protein. Several rpm1 mutants retain partial function, and we deduce that their residual activity is dependent on the level of avrRpm1 signal. In these mutants, the hypersensitive response remains activated if the signal goes above a certain threshold. Missense mutations in rpm1 are highly enriched in the nucleotide binding domain, suggesting that this region plays a key role either in the hypersensitive response associated with RPM1 activation or in RPM1 stability. Cluster analysis of rpm1 alleles defines functionally important residues that are highly conserved between nucleotide binding site leucine-rich repeat R proteins and those that are unique to RPM1. Regions of RPM1 to which no loss-of-function alleles map may represent domains in which variation is tolerated and may contribute to the evolution of new R gene specificities.
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Affiliation(s)
- Pablo Tornero
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA
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Mori K, Hata M, Neya S, Hoshino T. A study on the role of Mg2+ in a Ras protein by MD simulation. CHEM-BIO INFORMATICS JOURNAL 2002. [DOI: 10.1273/cbij.2.147] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Kenichi Mori
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences
| | - Masayuki Hata
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences
| | - Saburo Neya
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences
| | - Tyuji Hoshino
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences
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Hansen MD, Nelson WJ. Serum-activated assembly and membrane translocation of an endogenous Rac1:effector complex. Curr Biol 2001; 11:356-60. [PMID: 11267873 DOI: 10.1016/s0960-9822(01)00091-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Rho family GTPases (Cdc42, Rac1, and RhoA) function downstream of Ras [1], and in a variety of cellular processes [2]. Studies to examine these functions have not directly linked endogenous protein interactions with specific in vivo functions of Rho GTPases. Here, we show that endogenous Rac1 and two known binding partners, Rho GDP dissociation inhibitor (RhoGDI) and p21-activated kinase (PAK), fractionate as distinct cytosolic complexes. A Rac1:PAK complex is translocated from the cytosol to ruffling membranes upon cell activation by serum. Overexpression of dominant-negative (T17N) Rac1 does not affect the assembly or distribution of this Rac1:PAK complex. This is the first direct evidence of how a specific function of Rac1 is selected by the assembly and membrane translocation of a distinct Rac1:effector complex.
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Affiliation(s)
- M D Hansen
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, Stanford, CA 94305-5345, USA
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Farrar CT, Ma J, Singel DJ, Halkides CJ. Structural changes induced in p21Ras upon GAP-334 complexation as probed by ESEEM spectroscopy and molecular-dynamics simulation. Structure 2000; 8:1279-87. [PMID: 11188692 DOI: 10.1016/s0969-2126(00)00532-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND The means by which the protein GAP accelerates GTP hydrolysis, and thereby downregulates growth signaling by p21Ras, is of considerable interest, particularly inasmuch as p21 mutants are implicated in a number of human cancers. A GAP "arginine finger," identified by X-ray crystallography, has been suggested as playing the principal role in the GTP hydrolysis. Mutagenesis studies, however, have shown that the arginine can only partially account for the 10(5)-fold increase in the GAP-accelerated GTPase rate of p21. RESULTS We report electron spin-echo envelope modulation (ESEEM) studies of GAP-334 complexed with GMPPNP bound p21 in frozen solution, together with molecular-dynamics simulations. Our results indicate that, in solution, the association of GAP-334 with GTP bound p21 induces a conformational change near the metal ion active site of p21. This change significantly reduces the distances from the amide groups of p21 glycine residues 60 and 13 to the divalent metal ion. CONCLUSIONS The movement of glycine residues 60 and 13 upon the binding of GAP-334 in solution provides a physical basis to interpret prior mutagenesis studies, which indicated that Gly-60 and Gly-13 of p21 play important roles in the GAP-dependent GTPase reaction. Gly-60 and Gly-13 may play direct catalytic roles and stabilize the attacking water molecule and beta,gamma-bridging oxygen, respectively, in p21. The amide proton of Gly-60 could also play an indirect role in catalysis by supplying a crucial hydrogen bonding interaction that stabilizes loop L4 and therefore the position of other important catalytic residues.
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Affiliation(s)
- C T Farrar
- Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138, USA
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48
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Klockow B, Ahmadian MR, Block C, Wittinghofer A. Oncogenic insertional mutations in the P-loop of Ras are overactive in MAP kinase signaling. Oncogene 2000; 19:5367-76. [PMID: 11103938 DOI: 10.1038/sj.onc.1203909] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Mutations of Ras with three extra amino acids inserted into the phosphate-binding (P) loop have been investigated both in vitro and in vivo. Such mutants have originally been detected as oncogenes both in the ras and the TC21 genes. Biochemical experiments reveal the molecular basis of their oncogenic potential: the mutants show a strongly attenuated binding affinity for nucleotides, most notably for GDP, leading to a preference for GTP binding. Furthermore, both the intrinsic as well as the GAP-stimulated GTP hydrolysis are drastically diminished. The binding interaction with GAP is reduced, whereas binding to the Ras-binding domain of the downstream effector c-Raf1 is not altered appreciably. Microinjection into PC12 cells shows the mutants to be as potent to induce neurite outgrowth as conventional oncogenic Ras mutants. Unexpectedly, their ability to stimulate the MAP kinase pathway as measured by a reporter gene assay in RK13 cells is much higher than that of the normal oncogenic mutant G12V. This characteristic was attributed to an increased stimulation of c-Raf1 kinase activity by the insertional Ras mutants.
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Affiliation(s)
- B Klockow
- Max-Planck-Institut für molekulare Physiologie, Dortmund, Germany
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49
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Park J, Choi HJ, Lee S, Lee T, Yang Z, Lee Y. Rac-related GTP-binding protein in elicitor-induced reactive oxygen generation by suspension-cultured soybean cells. PLANT PHYSIOLOGY 2000; 124:725-32. [PMID: 11027721 PMCID: PMC59177 DOI: 10.1104/pp.124.2.725] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2000] [Accepted: 06/27/2000] [Indexed: 05/21/2023]
Abstract
Plant cells produce reactive oxygen species (ROS) in response to many stimuli. However, the mechanism of ROS biosynthesis remains unclear. We have explored the hypothesis that the superoxide burst in plants mechanistically resembles the oxidative burst in neutrophils. First we have confirmed that ROS production, which occurs in suspension-cultured soybean (Glycine max) cells in response to hypo-osmotic shock, is inhibited by diphenylene iodonium, an inhibitor of the flavin-dependent oxidase of neutrophils. Because a Rac family G protein is an essential regulator of this NADPH oxidase, and because many plant homologs of Rac have been cloned, we next examined whether Rac-like proteins might be involved in the oxidative burst in the soybean cells. We identified a Rac-like 21-kD soybean protein that cross-reacts with antibodies to human Rac and garden pea Rop and also binds [gamma-(35)S] GTP, a diagnostic trait of small G proteins. This Rac-related protein translocated from the cytosol to microsomes during the oxidative burst. Moreover, soybean cells transiently transformed with either a dominant negative (RacN17) or a dominant positive (RacV12) form of Rac1 showed the anticipated altered responses to three different stimuli: hypo-osmotic shock, oligo-GalUA, and harpin. In response to these stimuli, cells transformed with RacN17 produced less ROS and cells transformed with RacV12 generated more ROS than control cells. These results strongly suggest that a Rac-related protein participates in the regulation of ROS production in soybean cells, possibly via activation of an enzyme complex similar to the NADPH oxidase of phagocytes in animal systems.
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Affiliation(s)
- J Park
- Division of Molecular Life Science, Pohang University of Science and Technology, Pohang, 790-784, Korea
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50
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Palmieri SJ, Nebl T, Pope RK, Seastone DJ, Lee E, Hinchcliffe EH, Sluder G, Knecht D, Cardelli J, Luna EJ. Mutant Rac1B expression in Dictyostelium: effects on morphology, growth, endocytosis, development, and the actin cytoskeleton. CELL MOTILITY AND THE CYTOSKELETON 2000; 46:285-304. [PMID: 10962483 DOI: 10.1002/1097-0169(200008)46:4<285::aid-cm6>3.0.co;2-n] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Rac1 is a small G-protein in the Ras superfamily that has been implicated in the control of cell growth, adhesion, and the actin-based cytoskeleton. To investigate the role of Rac1 during motile processes, we have established Dictyostelium cell lines that conditionally overexpress epitope-tagged Dictyostelium discoideum wild-type Rac1B (DdRac1B) or a mutant DdRac1B protein. Expression of endogenous levels of myc- or GFP-tagged wild-type DdRac1B had minimal effect on cellular morphologies and behaviors. By contrast, expression of a constitutively active mutant (G12-->V or Q61-->L) or a dominant negative mutant (T17-->N) generated amoebae with characteristic cellular defects. The morphological appearance of actin-containing structures, intracellular levels of F-actin, and cellular responses to chemoattractant closely paralleled the amount of active DdRac1B, indicating a role in upregulating actin cytoskeletal activities. Expression of any of the three mutants inhibited cell growth and cytokinesis, and delayed multicellular development, suggesting that DdRac1B plays important regulatory role(s) during these processes. No significant effects were observed on binding or internalization of latex beads in suspension or on intracellular membrane trafficking. Cells expressing DdRac1B-G12V exhibited defects in fluid-phase endocytosis and the longest developmental delays; DdRac1B-Q61L produced the strongest cytokinesis defect; and DdRac1B-T17N generated intermediate phenotypes. These conditionally expressed DdRac1B proteins should facilitate the identification and characterization of the Rac1 signaling pathway in an organism that is amenable to both biochemical and molecular genetic manipulations.
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Affiliation(s)
- S J Palmieri
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, UK
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