51
|
Wang Y, Pascoe HG, Brautigam CA, He H, Zhang X. Structural basis for activation and non-canonical catalysis of the Rap GTPase activating protein domain of plexin. eLife 2013; 2:e01279. [PMID: 24137545 PMCID: PMC3787391 DOI: 10.7554/elife.01279] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Accepted: 08/22/2013] [Indexed: 12/14/2022] Open
Abstract
Plexins are cell surface receptors that bind semaphorins and transduce signals for regulating neuronal axon guidance and other processes. Plexin signaling depends on their cytoplasmic GTPase activating protein (GAP) domain, which specifically inactivates the Ras homolog Rap through an ill-defined non-canonical catalytic mechanism. The plexin GAP is activated by semaphorin-induced dimerization, the structural basis for which remained unknown. Here we present the crystal structures of the active dimer of zebrafish PlexinC1 cytoplasmic region in the apo state and in complex with Rap. The structures show that the dimerization induces a large-scale conformational change in plexin, which opens the GAP active site to allow Rap binding. Plexin stabilizes the switch II region of Rap in an unprecedented conformation, bringing Gln63 in Rap into the active site for catalyzing GTP hydrolysis. The structures also explain the unique Rap-specificity of plexins. Mutational analyses support that these mechanisms underlie plexin activation and signaling. DOI:http://dx.doi.org/10.7554/eLife.01279.001.
Collapse
Affiliation(s)
- Yuxiao Wang
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Heath G Pascoe
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Chad A Brautigam
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
| | - Huawei He
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Xuewu Zhang
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States
| |
Collapse
|
52
|
Hamby SE, Reviriego P, Cooper DN, Upadhyaya M, Chuzhanova N. Screening in silico predicted remotely acting NF1 gene regulatory elements for mutations in patients with neurofibromatosis type 1. Hum Genomics 2013; 7:18. [PMID: 23947441 PMCID: PMC3750751 DOI: 10.1186/1479-7364-7-18] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 08/11/2013] [Indexed: 11/10/2022] Open
Abstract
Neurofibromatosis type 1 (NF1), a neuroectodermal disorder, is caused by germline mutations in the NF1 gene. NF1 affects approximately 1/3,000 individuals worldwide, with about 50% of cases representing de novo mutations. Although the NF1 gene was identified in 1990, the underlying gene mutations still remain undetected in a small but obdurate minority of NF1 patients. We postulated that in these patients, hitherto undetected pathogenic mutations might occur in regulatory elements far upstream of the NF1 gene. In an attempt to identify such remotely acting regulatory elements, we reasoned that some of them might reside within DNA sequences that (1) have the potential to interact at distance with the NF1 gene and (2) lie within a histone H3K27ac-enriched region, a characteristic of active enhancers. Combining Hi-C data, obtained by means of the chromosome conformation capture technique, with data on the location and level of histone H3K27ac enrichment upstream of the NF1 gene, we predicted in silico the presence of two remotely acting regulatory regions, located, respectively, approximately 600 kb and approximately 42 kb upstream of the NF1 gene. These regions were then sequenced in 47 NF1 patients in whom no mutations had been found in either the NF1 or SPRED1 gene regions. Five patients were found to harbour DNA sequence variants in the distal H3K27ac-enriched region. Although these variants are of uncertain pathological significance and still remain to be functionally characterized, this approach promises to be of general utility for the detection of mutations underlying other inherited disorders that may be caused by mutations in remotely acting regulatory elements.
Collapse
Affiliation(s)
- Stephen E Hamby
- School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK
- Current address: Department of Cardiovascular Sciences, University of Leicester, Glenfield Hospital, Leicester LE3 9QP, UK
| | - Pablo Reviriego
- Institute of Medical Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK
| | - David N Cooper
- Institute of Medical Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK
| | - Meena Upadhyaya
- Institute of Medical Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK
| | - Nadia Chuzhanova
- School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK
| |
Collapse
|
53
|
Abstract
Small GTPases use GDP/GTP alternation to actuate a variety of functional switches that are pivotal for cell dynamics. The GTPase switch is turned on by GEFs, which stimulate dissociation of the tightly bound GDP, and turned off by GAPs, which accelerate the intrinsically sluggish hydrolysis of GTP. For Ras, Rho, and Rab GTPases, this switch incorporates a membrane/cytosol alternation regulated by GDIs and GDI-like proteins. The structures and core mechanisms of representative members of small GTPase regulators from most families have now been elucidated, illuminating their general traits combined with scores of unique features. Recent studies reveal that small GTPase regulators have themselves unexpectedly sophisticated regulatory mechanisms, by which they process cellular signals and build up specific cell responses. These mechanisms include multilayered autoinhibition with stepwise release, feedback loops mediated by the activated GTPase, feed-forward signaling flow between regulators and effectors, and a phosphorylation code for RhoGDIs. The flipside of these highly integrated functions is that they make small GTPase regulators susceptible to biochemical abnormalities that are directly correlated with diseases, notably a striking number of missense mutations in congenital diseases, and susceptible to bacterial mimics of GEFs, GAPs, and GDIs that take command of small GTPases in infections. This review presents an overview of the current knowledge of these many facets of small GTPase regulation.
Collapse
Affiliation(s)
- Jacqueline Cherfils
- Laboratoire d’Enzymologie et Biochimie Structurales, Centre National de la Recherche Scientifique, Centre deRecherche de Gif, Gif-sur-Yvette, France
| | | |
Collapse
|
54
|
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.
Collapse
Affiliation(s)
- Sybille Lorenz
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany
| | | | | | | | | | | | | |
Collapse
|
55
|
|
56
|
Deo M, Huang JLY, Fuchs H, de Angelis MH, Van Raamsdonk CD. Differential Effects of Neurofibromin Gene Dosage on Melanocyte Development. J Invest Dermatol 2013; 133:49-58. [DOI: 10.1038/jid.2012.240] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
|
57
|
Baker R, Lewis SM, Sasaki AT, Wilkerson EM, Locasale JW, Cantley LC, Kuhlman B, Dohlman HG, Campbell SL. Site-specific monoubiquitination activates Ras by impeding GTPase-activating protein function. Nat Struct Mol Biol 2012. [PMID: 23178454 PMCID: PMC3537887 DOI: 10.1038/nsmb.2430] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Cell growth and differentiation are controlled by growth factor receptors coupled to the GTPase Ras. Oncogenic mutations disrupt GTPase activity leading to persistent Ras signaling and cancer progression. Recent evidence indicates that monoubiquitination of Ras leads to Ras activation. Mutation of the primary site of monoubiquitination impairs the ability of activated K–Ras to promote tumor growth. To determine the mechanism of human Ras activation we chemically ubiquitinated the protein and analyzed its function by NMR, computational modeling, and biochemical activity measurements. We established that monoubiquitination has little effect on Ras GTP binding, GTP hydrolysis, or exchange factor activation, but severely abrogates the response to GTPase activating proteins in a site–specific manner. These findings reveal a new mechanism by which Ras can trigger persistent signaling in the absence of receptor activation or an oncogenic mutation.
Collapse
Affiliation(s)
- Rachael Baker
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
58
|
Thomas L, Richards M, Mort M, Dunlop E, Cooper DN, Upadhyaya M. Assessment of the potential pathogenicity of missense mutations identified in the GTPase-activating protein (GAP)-related domain of the neurofibromatosis type-1 (NF1) gene. Hum Mutat 2012; 33:1687-96. [PMID: 22807134 DOI: 10.1002/humu.22162] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Accepted: 06/28/2012] [Indexed: 11/09/2022]
Abstract
Neurofibromatosis type-1 (NF1) is caused by constitutional mutations of the NF1 tumor-suppressor gene. Although ∼85% of inherited NF1 microlesions constitute truncating mutations, the remaining ∼15% are missense mutations whose pathological relevance is often unclear. The GTPase-activating protein-related domain (GRD) of the NF1-encoded protein, neurofibromin, serves to define its major function as a negative regulator of the Ras-MAPK (mitogen-activated protein kinase) signaling pathway. We have established a functional assay to assess the potential pathogenicity of 15 constitutional nonsynonymous NF1 missense mutations (11 novel and 4 previously reported but not functionally characterized) identified in the NF1-GRD (p.R1204G, p.R1204W, p.R1276Q, p.L1301R, p.I1307V, p.T1324N, p.E1327G, p.Q1336R, p.E1356G, p.R1391G, p.V1398D, p.K1409E, p.P1412R, p.K1436Q, p.S1463F). Individual mutations were introduced into an NF1-GRD expression vector and activated Ras was assayed by an enzyme-linked immunosorbent assay (ELISA). Ten NF1-GRD variants were deemed to be potentially pathogenic by virtue of significantly elevated levels of activated GTP-bound Ras in comparison to wild-type NF1 protein. The remaining five NF1-GRD variants were deemed less likely to be of pathological significance as they exhibited similar levels of activated Ras to the wild-type protein. These conclusions received broad support from both bioinformatic analysis and molecular modeling and serve to improve our understanding of NF1-GRD structure and function.
Collapse
Affiliation(s)
- Laura Thomas
- Institute of Medical Genetics, Cardiff University, Cardiff, UK
| | | | | | | | | | | |
Collapse
|
59
|
Heo JB, Sung S, Assmann SM. Ca2+-dependent GTPase, extra-large G protein 2 (XLG2), promotes activation of DNA-binding protein related to vernalization 1 (RTV1), leading to activation of floral integrator genes and early flowering in Arabidopsis. J Biol Chem 2012; 287:8242-53. [PMID: 22232549 DOI: 10.1074/jbc.m111.317412] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Heterotrimeric G proteins, consisting of Gα, Gβ, and Gγ subunits, play important roles in plant development and cell signaling. In Arabidopsis, in addition to one prototypical G protein α subunit, GPA1, there are three extra-large G proteins, XLG1, XLG2, and XLG3, of largely unknown function. Each extra-large G (XLG) protein has a C-terminal Gα-like region and a ∼400 amino acid N-terminal extension. Here we show that the three XLG proteins specifically bind and hydrolyze GTP, despite the fact that these plant-specific proteins lack key conserved amino acid residues important for GTP binding and hydrolysis of GTP in mammalian Gα proteins. Moreover, unlike other known Gα proteins, these activities require Ca(2+) instead of Mg(2+) as a cofactor. Yeast two-hybrid library screening and in vitro protein pull-down assays revealed that XLG2 interacts with the nuclear protein RTV1 (related to vernalization 1). Electrophoretic mobility shift assays show that RTV1 binds to DNA in vitro in a non-sequence-specific manner and that GTP-bound XLG2 promotes the DNA binding activity of RTV1. Overexpression of RTV1 results in early flowering. Combined overexpression of XLG2 and RTV1 enhances this early flowering phenotype and elevates expression of the floral pathway integrator genes, FT and SOC1, but does not repress expression of the floral repressor, FLC. Chromatin immunoprecipitation assays show that XLG2 increases RTV1 binding to FT and SOC1 promoters. Thus, a Ca(2+)-dependent G protein, XLG2, promotes RTV1 DNA binding activity for a subset of floral integrator genes and contributes to floral transition.
Collapse
Affiliation(s)
- Jae Bok Heo
- Department of Biology, Penn State University, University Park, Pennsylvania 16802, USA
| | | | | |
Collapse
|
60
|
Stefanaki K, Alexiou GA, Stefanaki C, Prodromou N. Tumors of central and peripheral nervous system associated with inherited genetic syndromes. Pediatr Neurosurg 2012; 48:271-85. [PMID: 23796843 DOI: 10.1159/000351546] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Accepted: 04/18/2013] [Indexed: 11/19/2022]
Abstract
There are several genetic syndromes that predispose to the development of tumors of the nervous system. In the present study, we provide a review of the tumors that are associated with neurofibromatosis type 1, neurofibromatosis type 2, tuberous sclerosis complex, von Hippel-Lindau disease, Li-Fraumeni syndrome, Cowden disease, Turcot syndrome, nevoid basal cell carcinoma syndrome (Gorlin syndrome) and rhabdoid predisposition syndrome, which are the most common.
Collapse
|
61
|
Gabriele AL, Ruggieri M, Patitucci A, Magariello A, Conforti FL, Mazzei R, Muglia M, Ungaro C, Di Palma G, Citrigno L, Sproviero W, Gambardella A, Quattrone A. A novel NF1 gene mutation in an Italian family with neurofibromatosis type 1. Childs Nerv Syst 2011; 27:635-8. [PMID: 20927530 DOI: 10.1007/s00381-010-1282-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Accepted: 09/09/2010] [Indexed: 11/26/2022]
Abstract
PURPOSE Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder with an estimated incidence of one in 3,500 births. Clinically, NF1 is characterized by café-au-lait (CAL) spots, neurofibromas, freckling of the axillary or inguinal region, Lisch nodules, optic nerve glioma, and bone dysplasias. NF1 is caused by inactivating mutations of the 17q11.2-located NF1 gene. We present a clinical and molecular study of an Italian family with NF1. METHODS The proband, a 10-year-old boy, showed large CAL spots and freckling on the axillary region and plexiform neurofibromas on the right side only. His father (47 years old) showed, in addition to the similar signs, numerous neurofibromas of various sizes on his thorax, abdomen, back, and shoulder. Two additional family members (a brother and a sister of the proband) presented only small CAL spots. The coding exons of NF1 gene were analyzed for mutations by denaturing high-performance liquid chromatography and sequencing in all family members. RESULTS The mutational analysis of the NF1 gene revealed a novel frameshift insertion mutation in exon 4c (c.654 ins A) in all affected family members. This novel mutation creates a shift on the reading frame starting at codon 218 and leads to the introduction of a premature stop at codon 227. CONCLUSIONS The segregation of the mutation with the affected phenotype and its absence in the 200 normal chromosomes suggest that it is responsible for the NF1 phenotype.
Collapse
Affiliation(s)
- Anna Lia Gabriele
- Institute of Neurological Science (ISN), National Research Council (CNR), Piano Lago di Mangone, Cosenza, Italy.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
62
|
Lam R, Romanov V, Johns K, Battaile KP, Wu-Brown J, Guthrie JL, Hausinger RP, Pai EF, Chirgadze NY. Crystal structure of a truncated urease accessory protein UreF from Helicobacter pylori. Proteins 2011; 78:2839-48. [PMID: 20635345 DOI: 10.1002/prot.22802] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Urease plays a central role in the pathogenesis of Helicobacter pylori in humans. Maturation of this nickel metalloenzyme in bacteria requires the participation of the accessory proteins UreD (termed UreH in H. pylori), UreF, and UreG, which form sequential complexes with the urease apoprotein as well as UreE, a metallochaperone. Here, we describe the crystal structure of C-terminal truncated UreF from H. pylori (residues 1-233), the first UreF structure to be determined, at 1.55 A resolution using SAD methods. UreF forms a dimer in vitro and adopts an all-helical fold congruent with secondary structure prediction. On the basis of evolutionary conservation analysis, the structure reveals a probable binding surface for interaction with other urease components as well as key conserved residues of potential functional relevance.
Collapse
Affiliation(s)
- Robert Lam
- Division of Cancer Genomics and Proteomics, Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2C4, Canada
| | | | | | | | | | | | | | | | | |
Collapse
|
63
|
Welti S, Kühn S, D'Angelo I, Brügger B, Kaufmann D, Scheffzek K. Structural and biochemical consequences of NF1 associated nontruncating mutations in the Sec14-PH module of neurofibromin. Hum Mutat 2011; 32:191-7. [PMID: 21089070 DOI: 10.1002/humu.21405] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Accepted: 10/26/2010] [Indexed: 11/06/2022]
Abstract
Neurofibromatosis type 1 (NF1) is a common genetic disorder caused by alterations in the tumor suppressor gene NF1. Clinical manifestations include various neural crest derived tumors, pigmentation anomalies, bone deformations, and learning disabilities. NF1 encodes the Ras specific GTPase activating protein (RasGAP) neurofibromin, of which the central RasGAP related domain as well as a Sec14-like (residues 1560-1699) and a tightly interacting pleckstrin homology (PH)-like (1713-1818) domain are currently well defined. However, patient-derived nontruncating mutations have been reported along the whole NF1 gene, suggesting further essential protein functions. Focusing on the Sec14-PH module, we have engineered such nontruncating mutations and analyzed their implications on protein function and structure using lipid binding assays, CD spectroscopy and X-ray crystallography. Although lipid binding appears to be preserved among most nontruncating mutants, we see major structural changes for two of the alterations. Judging from these changes and our biochemical data, we suggest the presence of an intermolecular contact surface in the lid-lock region of the protein.
Collapse
Affiliation(s)
- Stefan Welti
- European Molecular Biology Laboratory (EMBL), Structural and Computational Biology Unit, Heidelberg, Germany.
| | | | | | | | | | | |
Collapse
|
64
|
Kweh F, Zheng M, Kurenova E, Wallace M, Golubovskaya V, Cance WG. Neurofibromin physically interacts with the N-terminal domain of focal adhesion kinase. Mol Carcinog 2009; 48:1005-17. [PMID: 19479903 PMCID: PMC2783617 DOI: 10.1002/mc.20552] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The NF1 gene that is altered in patients with type 1 neurofibromatosis (NF1) encodes a neurofibromin protein that functions as a tumor suppressor. In this report, we show for the first time physical interaction between neurofibromin and focal adhesion kinase (FAK), the protein that localizes at focal adhesions. We show that neurofibromin associates with the N-terminal domain of FAK, and that the C-terminal domain of neurofibromin directly interacts with FAK. Confocal microscopy demonstrates colocalization of NF1 and FAK in the cytoplasm, perinuclear and nuclear regions inside the cells. Nf1+/+ MEF cells expressed less cell growth during serum deprivation conditions, and adhered less on collagen and fibronectin-treated plates than Nf1(-/-) MEF cells, associated with changes in actin and FAK staining. In addition, Nf1+/+ MEF cells detached more significantly than Nf1(-/-) MEF cells by disruption of FAK signaling with the dominant-negative inhibitor of FAK, C-terminal domain of FAK (FAK-CD). Thus, the results demonstrate the novel interaction of neurofibromin and FAK and suggest their involvement in cell adhesion, cell growth, and other cellular events and pathways.
Collapse
Affiliation(s)
- Frederick Kweh
- Department of Surgery, University of Florida, Gainesville, Florida
- University of Florida Shands Cancer Center, Gainesville, Florida
| | - Min Zheng
- Department of Surgery, University of Florida, Gainesville, Florida
- University of Florida Shands Cancer Center, Gainesville, Florida
| | - Elena Kurenova
- Department of Surgery, University of Florida, Gainesville, Florida
- University of Florida Shands Cancer Center, Gainesville, Florida
| | - Margaret Wallace
- Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida
| | | | | |
Collapse
|
65
|
Crystal structure of the plexin A3 intracellular region reveals an autoinhibited conformation through active site sequestration. Proc Natl Acad Sci U S A 2009; 106:15610-5. [PMID: 19717441 DOI: 10.1073/pnas.0906923106] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Plexin cell surface receptors bind to semaphorin ligands and transduce signals for regulating neuronal axon guidance. The intracellular region of plexins is essential for signaling and contains a R-Ras/M-Ras GTPase activating protein (GAP) domain that is divided into two segments by a Rho GTPase-binding domain (RBD). The regulation mechanisms for plexin remain elusive, although it is known that activation requires both binding of semaphorin to the extracellular region and a Rho-family GTPase (Rac1 or Rnd1) to the RBD. Here we report the crystal structure of the plexin A3 intracellular region. The structure shows that the N- and C-terminal portions of the GAP homologous regions together form a GAP domain with an overall fold similar to other Ras GAPs. However, the plexin GAP domain adopts a closed conformation and cannot accommodate R-Ras/M-Ras in its substrate-binding site, providing a structural basis for the autoinhibited state of plexins. A comparison with the plexin B1 RBD/Rnd1 complex structure suggests that Rnd1 binding alone does not induce a conformational change in plexin, explaining the requirement of both semaphorin and a Rho GTPase for activation. The structure also identifies an N-terminal segment that is important for regulation. Both the N-terminal segment and the RBD make extensive interactions with the GAP domain, suggesting the presence of an allosteric network connecting these three domains that integrates semaphorin and Rho GTPase signals to activate the GAP. The importance of these interactions in plexin signaling is shown by both cell-based and in vivo axon guidance assays.
Collapse
|
66
|
Du X, Sprang SR. Transition state structures and the roles of catalytic residues in GAP-facilitated GTPase of Ras as elucidated by (18)O kinetic isotope effects. Biochemistry 2009; 48:4538-47. [PMID: 19610677 DOI: 10.1021/bi802359b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ras-catalyzed guanosine 5' triphosphate (GTP) hydrolysis proceeds through a loose transition state as suggested in our previous study of (18)O kinetic isotope effects (KIE) [ Du , X. et al. ( 2004 ) Proc. Natl. Acad. Sci. U.S.A. 101 , 8858 - 8863 ]. To probe the mechanisms of GTPase activation protein (GAP)-facilitated GTP hydrolysis reactions, we measured the (18)O KIEs in GTP hydrolysis catalyzed by Ras in the presence of GAP(334) or NF1(333), the catalytic fragment of p120GAP or NF1. The KIEs in the leaving group oxygens (the beta nonbridge and the beta-gamma bridge oxygens) reveal that chemistry is rate-limiting in GAP(334)-facilitated GTP hydrolysis but only partially rate-limiting in the NF1(333)-facilitated GTP hydrolysis reaction. The KIEs in the gamma nonbridge oxygens and the leaving group oxygens reveal that the GAP(334) or NF1(333)-facilitated GTP hydrolysis reaction proceeds through a loose transition state that is similar in nature to the transition state of the GTP hydrolysis catalyzed by Ras alone. However, the KIEs in the pro-S beta, pro-R beta, and beta-gamma oxygens suggest that charge increase on the beta-gamma bridge oxygen is more prominent in the transition states of GAP(334)- and NF1(333)-facilitated reactions than that catalyzed by the intrinsic GTPase activity of Ras. The charge distribution on the two beta nonbridge oxygens is also very asymmetric. The catalytic roles of active site residues were inferred from the effect of mutations on the reaction rate and KIEs. Our results suggest that the arginine finger of GAP and amide protons in the P-loop of Ras stabilize the negative charge on the beta-gamma bridge oxygen and the pro-S beta nonbridge oxygen of a loose transition state, whereas Lys-16 of Ras and Mg(2+) are only involved in substrate binding.
Collapse
Affiliation(s)
- Xinlin Du
- Department of Biochemistry, University of Texas, Southwestern Medical Center, 6001 Forest Park, Room ND10.300, Dallas, Texas 75390-9050, USA
| | | |
Collapse
|
67
|
Yang Q, Huang C, Yang X, Feng Y, Wang Q, Liu M. The R1947X mutation of NF1 causing autosomal dominant neurofibromatosis type 1 in a Chinese family. J Genet Genomics 2009; 35:73-6. [PMID: 18407053 DOI: 10.1016/s1673-8527(08)60011-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Revised: 10/24/2007] [Accepted: 10/25/2007] [Indexed: 10/22/2022]
Abstract
Neurofibromatosis type 1 is a common autosomal dominant disorder with a high rate of penetrance. It is caused by the mutation of the tumor suppressor gene NF1, which encodes neurofibromin. The main function of neurofibromin is down-regulating the biological activity of the proto-oncoprotein Ras by acting as a Ras-specific GTPase activating protein. In this study, we identified a Chinese family affected with neurofibromatosis type 1. The known gene NF1 associated with NF1 was studied by linkage analysis and by direct sequencing of the entire coding region and exon-intron boundaries of the NF1 gene. The R1947X mutation of NF1 was identified, which was co-segregated with affected individuals in the Chinese family, but not present in unaffected family members. This is the first report, which states that the R1947X mutation of NF1 may be one of reasons for neurofibromatosis type 1 in Chinese population.
Collapse
Affiliation(s)
- Qinbo Yang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, and Center for Human Genome Research, Huazhong University of Science and Technology, Wuhan, China
| | | | | | | | | | | |
Collapse
|
68
|
Kurella VB, Richard JM, Parke CL, Lecour LF, Bellamy HD, Worthylake DK. Crystal structure of the GTPase-activating protein-related domain from IQGAP1. J Biol Chem 2009; 284:14857-65. [PMID: 19321438 DOI: 10.1074/jbc.m808974200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
IQGAP1 is a 190-kDa molecular scaffold containing several domains required for interaction with numerous proteins. One domain is homologous to Ras GTPase-activating protein (GAP) domains. However, instead of accelerating hydrolysis of bound GTP on Ras IQGAP1, using its GAP-related domain (GRD) binds to Cdc42 and Rac1 and stabilizes their GTP-bound states. We report here the crystal structure of the isolated IQGAP1 GRD. Despite low sequence conservation, the overall structure of the GRD is very similar to the GAP domains from p120 RasGAP, neurofibromin, and SynGAP. However, instead of the catalytic "arginine finger" seen in functional Ras GAPs, the GRD has a conserved threonine residue. GRD residues 1099-1129 have no structural equivalent in RasGAP and are seen to form an extension at one end of the molecule. Because the sequence of these residues is highly conserved, this region likely confers a functionality particular to IQGAP family GRDs. We have used isothermal titration calorimetry to demonstrate that the isolated GRD binds to active Cdc42. Assuming a mode of interaction similar to that displayed in the Ras-RasGAP complex, we created an energy-minimized model of Cdc42.GTP bound to the GRD. Residues of the GRD that contact Cdc42 map to the surface of the GRD that displays the highest level of sequence conservation. The model indicates that steric clash between threonine 1046 with the phosphate-binding loop and other subtle changes would likely disrupt the proper geometry required for GTP hydrolysis.
Collapse
Affiliation(s)
- Vinodh B Kurella
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA
| | | | | | | | | | | |
Collapse
|
69
|
Bonneau F, Lenherr ED, Pena V, Hart DJ, Scheffzek K. Solubility survey of fragments of the neurofibromatosis type 1 protein neurofibromin. Protein Expr Purif 2008; 65:30-7. [PMID: 19111619 DOI: 10.1016/j.pep.2008.12.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Revised: 12/02/2008] [Accepted: 12/02/2008] [Indexed: 12/13/2022]
Abstract
The protein giant neurofibromin (320kDa) is the protein product of the NF1 tumor suppressor gene, alterations of which are responsible for the pathogenesis of neurofibromatosis type 1 (NF1). Neurofibromin is a Ras-specific GTPase activating protein (RasGAP) that, 15 years after the cloning of the gene, remains the only clearly defined function of the protein. In a structural proteomics approach, we aimed at defining functions beyond RasGAP activity based on the discovery of structural modules. Given the poor outcome of domain prediction tools, we have undertaken a fragment solubility survey covering the full protein sequence, with the aim of defining new domain boundaries or fragments that could be investigated by biochemical methods including structural analysis. More than 200 constructs have been expressed and tested for solubility in small scale assays. Boundaries were chosen based upon secondary structure predictions, sequence conservation among neurofibromin orthologues and chemical properties of amino acids. Using this strategy we recently discovered a novel bipartite module in neurofibromin. We have expanded our study to include ESPRIT, a library-based construct screen, to perform fragment testing at a finer level with respect to the choice of terminal residues. Our study confirms earlier notions about the challenges neurofibromin presents to the biochemist and points to strategies whereby the success rate may be enhanced in the future.
Collapse
Affiliation(s)
- Fabien Bonneau
- European Laboratory of Molecular Biology (EMBL), Structural & Computational Biology and Developmental Biology Units, Meyerhofstrasse 1, D-69117 Heidelberg, Germany
| | | | | | | | | |
Collapse
|
70
|
Gremer L, Gilsbach B, Ahmadian MR, Wittinghofer A. Fluoride complexes of oncogenic Ras mutants to study the Ras-RasGap interaction. Biol Chem 2008; 389:1163-71. [PMID: 18713003 DOI: 10.1515/bc.2008.132] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Down-regulation of Ras signalling is mediated by specific GTPase-activating proteins (GAPs), which stimulate the very slow GTPase reaction of Ras by 10(5)-fold. The basic features of the GAP activity involve the stabilisation of both switch regions of Ras in the transition state, and the insertion of an arginine finger. In the case of oncogenic Ras mutations, the features of the active site are disturbed. To understand these features in more detail, we have investigated the effects of oncogenic mutations of Ras and compared the GAP-stimulated GTPase reaction with the ability to form GAP-mediated aluminium or beryllium fluoride complexes. In general we find a correlation between the size of the amino acid at position 12, the GTPase activity and ability to form aluminium fluoride complexes. While Gly12 is very sensitive to even the smallest possible structural change, Gly13 is much less sensitive to steric hindrance, but is sensitive to charge. Oncogenic mutants of Ras defective in the GTPase activity can however form ground-state GppNHp complexes with GAP, which can be mimicked by beryllium fluoride binding. We show that beryllium fluoride complexes are less sensitive to structural changes and report on a state close to but different from the ground state of the GAP-stimulated GTPase reaction.
Collapse
Affiliation(s)
- Lothar Gremer
- Abteilung Strukturelle Biologie, Max-Planck-Institut für molekulare Physiologie, Otto-Hahn-Strasse 11, D-44227 Dortmund, Germany
| | | | | | | |
Collapse
|
71
|
Hirosawa-Takamori M, Ossipov D, Novoselov SV, Turanov AA, Zhang Y, Gladyshev VN, Krol A, Vorbrüggen G, Jäckle H. A novel stem loop control element-dependent UGA read-through system without translational selenocysteine incorporation in Drosophila. FASEB J 2008; 23:107-13. [PMID: 18772345 DOI: 10.1096/fj.08-116640] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Translational read-through of the UGA stop codon is an evolutionarily conserved feature that most prominently represents the basis of selenoprotein biosynthesis. It requires a specific cis-acting stem loop control element, termed SECIS, which is located in the 3'-untranslated region of eukaryotic selenoprotein mRNAs. In a search for novel factors underlying the SECIS-directed UGA read-through process, we identified an evolutionary conserved GTPase-activating protein, termed GAPsec. We show that the activity of the Drosophila GAPsec (dGAPsec) is necessary to support SECIS-dependent UGA read-through activity in flies and the mouse homolog mGAPsec in mice tissue culture cells. However, selenoprotein biosynthesis is not impaired in flies that lack dGAPsec activity. The results indicate that GAPsec is part of a novel SECIS-dependent translational read-through system that does not involve selenocysteine incorporation.
Collapse
Affiliation(s)
- Mitsuko Hirosawa-Takamori
- Max-Planck-Institut für biophysikalische Chemie, Abteilung Molekulare Entwicklungsbiologie, Am Fassberg 11, 37077 Göttingen, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
72
|
Huang YH, Yang QB, Deng YH, Yu NW, Wang Q, Liu MG. [NF1 mutation analysis in a Chinese family with neuro- fibromatosis type]. YI CHUAN = HEREDITAS 2008; 30:309-312. [PMID: 18331998 DOI: 10.3724/sp.j.1005.2008.00309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A Chinese family affected with autosomal dominant disorder-neurofibromatosis type I was identified in this study. Linkage analysis was performed, and DNA sequencing for whole coding region of NF1 was carried out to identify the disease-causing mutation. The disease gene of the Chinese NF1 family was linked to NF1 locus, and a nonsense mutation, G1336X in the NF1 gene was identified. This mutation truncates the NF1 protein by 1 483 amino acid residues at the C-terminus, and is co-segregate with all the patients, but not present in unaffected individuals in the family. The present study demonstrated that G1336X mutation in the NF1 gene cause Neurofibromatosis type I in the family. To our knowledge, this mutation is firstly reported in Chinese population.
Collapse
Affiliation(s)
- Ying-Hao Huang
- Huazhong University of Science and Technology, Wuhan 430074, China.
| | | | | | | | | | | |
Collapse
|
73
|
Alotaibi H, Ricciardone MD, Ozturk M. Homozygosity at variant MLH1 can lead to secondary mutation in NF1, neurofibromatosis type I and early onset leukemia. Mutat Res 2008; 637:209-14. [PMID: 17889038 DOI: 10.1016/j.mrfmmm.2007.08.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Revised: 07/30/2007] [Accepted: 08/01/2007] [Indexed: 05/17/2023]
Abstract
Heterozygous germ-line variants of DNA mismatch repair (MMR) genes predispose individuals to hereditary non-polyposis colorectal cancer. Several independent reports have shown that individuals constitutionally homozygous for MMR allelic variants develop early onset hematological malignancies often associated to features of neurofibromatosis type 1 (NF1) syndrome. The genetic mechanism of NF1 associated to MMR gene deficiency is not fully known. We report here that a child with this form of NF1 displays a heterozygous NF1 gene mutation (c.3721C>T), in addition to a homozygous MLH1 gene mutation (c.676C>T) leading to a truncated MLH1 protein (p.R226X). The parents did not display NF1 features nor the NF1 mutation. This new NF1 gene mutation is recurrent and predicts a truncated neurofibromin (p.R1241X) lacking its GTPase activating function, as well as all C-terminally located functional domains. Our findings suggest that NF1 disease observed in individuals homozygous for deleterious MMR variants may be due to a concomitant NF1 gene mutation. The presence of both homozygous MLH1 and heterozygous NF1 mutation in the child studied here also provides a mechanistic explanation for early onset malignancies that are observed in affected individuals. It also provides a model for cooperation between genetic alterations in human carcinogenesis.
Collapse
Affiliation(s)
- Hani Alotaibi
- Bilkent University, Department of Molecular Biology and Genetics, 06800, Ankara, Turkey
| | | | | |
Collapse
|
74
|
Du X, Ferguson K, Gregory R, Sprang SR. A method to determine 18 O kinetic isotope effects in the hydrolysis of nucleotide triphosphates. Anal Biochem 2007; 372:213-21. [PMID: 17963711 DOI: 10.1016/j.ab.2007.09.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2007] [Revised: 08/02/2007] [Accepted: 09/11/2007] [Indexed: 11/25/2022]
Abstract
A method to determine 18 O kinetic isotope effects (KIEs) in the hydrolysis of GTP that is generally applicable to reactions involving other nucleotide triphosphates is described. Internal competition, where the substrate of the reaction is a mixture of 18 O-labeled and unlabeled nucleotides, is employed, and the change in relative abundance of the two species in the course of the reaction is used to calculate KIE. The nucleotide labeled with 18 O at sites of mechanistic interest also contains 13C at all carbon positions, whereas the 16 O-labeled nucleotide is depleted of 13C. The relative abundance of the labeled and unlabeled substrates or products is reflected in the carbon isotope ratio (13C/12C) in GTP or GDP, which is determined by the use of a liquid chromatography-coupled isotope ratio mass spectrometer (LC-coupled IRMS). The LC is coupled to the IRMS by an Isolink interface. Carbon isotope ratios can be determined with accuracy and precision greater than 0.04% and are consistent over an order of magnitude in sample amount. KIE values for Ras/NF1(333)-catalyzed hydrolysis of [beta18 O3,13C]GTP were determined by change in the isotope ratio of GTP or GDP or the ratio of the isotope ratio of GDP to that of GTP. KIE values computed in the three ways agree within 0.1%, although the method using the ratio of isotope ratios of GDP and GTP gives superior precision (<0.1%). A single KIE measurement can be conducted in 25 min with less than 5 microg nucleotide reaction product.
Collapse
Affiliation(s)
- Xinlin Du
- Department of Biochemistry, University of Texas, Southwestern Medical Center, Dallas, TX 75390, USA.
| | | | | | | |
Collapse
|
75
|
Bendova S, Krepelova A, Petrak B, Kinstova L, Musova Z, Rausova E, Marikova T. Novel mutations in the NF1 gene in Czech patients with neurofibromatosis type 1. J Mol Neurosci 2007; 31:273-9. [PMID: 17726231 DOI: 10.1385/jmn:31:03:273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2006] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 11/11/2022]
Abstract
Neurofibromatosis type 1 (NF1) is one of the most common inherited human disorders, with an estimated incidence of 1 per 3500 births. In most cases, the disease is caused either by mutation in the NF1 gene, or by a particular or complete deletion of the NF1 gene. The NF1 gene exhibits one of the highest mutation rates of any human disorder. In this experimental study of the NF1 gene, we screened the mutational spectrum of 22 unrelated patients from the Czech Republic using the denaturing high-performance liquid chromatography (DHPLC) and multiplex ligation-dependent probe amplification (MLPA) methods. We found NF1 mutations in 17 patients: 15 causal mutations were detected with the use of the DHPLC method (15/20, 75%). With the MPLA method, we also confirmed and specified two large deletions that were previously genotyped by microsatellite markers. Twelve of the above-mentioned mutations were newly found: c.1_2delATinsCC, c.1185+1G>C, c.1757_1760delCTAG, c.1642-7A>G, c.2329 T>G, c.2816delA, c.3738_3741delGTTT, c.4733 C>T, c.5220delT, c.6473_6474insGAAG, ex14_49del, ex28_49del. We present this study as a first effectual step in the routine diagnosis of the NF1 in patients from the Czech Republic.
Collapse
Affiliation(s)
- Sarka Bendova
- Institute of Biology and Medical Genetics, University Hospital Motol, 2nd School of Medicine, Charles University, Prague, Czech Republic.
| | | | | | | | | | | | | |
Collapse
|
76
|
Püschel AW. GTPases in semaphorin signaling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 600:12-23. [PMID: 17607943 DOI: 10.1007/978-0-387-70956-7_2] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A hallmark of semaphorin receptors is their interaction with multiple GTPases. Plexins, the signal transducing component of semaphorin receptors, directly associate with several GTPases. In addition, they not only recruit guaninine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs) but also are the only known integral membrane proteins that show a catalytic activity as GAPs for small GTPases. GTPases function upstream of semaphorin receptors and regulate the activity of plexins through an interaction with the cytoplasmic domain. The association of Plexin-Al (Sema3A receptor) or Plexin-B1 (Sema4D receptor) with the GTPase Rnd1 and ligand-dependent receptor clustering are required for their activity as R-Ras GAPs. The GTPases R-Ras and Rho function downstream of plexins and are required for the repulsive effects of semaphorins. In this review, I will focus on the role of GTPases in signaling by two plexins that have been analyzed in most detail, Plexin-A1 and Plexin-B1.
Collapse
Affiliation(s)
- Andreas W Püschel
- Abteilung Molekularbiologie, Institut für Allgemeine Zoologie und Genetik, Westfälische Wilhelms-Universität, Schlogplatz 5, 48149 Münster, Germany.
| |
Collapse
|
77
|
Welti S, Fraterman S, D'Angelo I, Wilm M, Scheffzek K. The sec14 homology module of neurofibromin binds cellular glycerophospholipids: mass spectrometry and structure of a lipid complex. J Mol Biol 2006; 366:551-62. [PMID: 17187824 DOI: 10.1016/j.jmb.2006.11.055] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2006] [Revised: 11/12/2006] [Accepted: 11/15/2006] [Indexed: 11/30/2022]
Abstract
Neurofibromin is the protein product of the tumor suppressor gene NF1, alterations of which are responsible for the pathogenesis of the common disorder Neurofibromatosis type I (NF1). The only well-characterized function of neurofibromin is its RasGAP activity, contained in the central GAP related domain (GRD). By solving the crystal structure of a 31 kDa fragment at the C-terminal end of the GRD we have recently identified a novel bipartite lipid-binding module composed of a Sec14 homologous and a previously undetected pleckstrin homology (PH)-like domain. Using lipid exchange assays along with mass spectrometry we show here that the Sec14-like portion binds to 1-(3-sn-phosphatidyl)-sn-glycerol (PtdGro), (3-sn-phosphatidyl)-ethanolamine (PtdEtn) and -choline (PtdCho) and to a minor extent to (3-sn-phosphatidyl)-l-serine (PtdSer) and 1-(3-sn-phosphatidyl)-d-myo-inositol (PtdIns). Phosphorylated PtdIns (PtdInsPs) are not detected as binders in the mass spectrometry assay, but their soluble inositol-phosphate headgroups and related compounds can inhibit the lipid exchange reaction. We also present here the crystal structure of this module with the Sec14 portion bound to a cellular glycerophospholipid ligand. Our structure has model character for the substrate-bound form of yeast Sec14p, of which only detergent bound structures are available so far. To assess potential regulation of the lipid exchange reaction in detail, we present a novel strategy using nanospray mass spectrometry. Ion intensities of initial phospholipids and exchanged deuterated analogues bound by the protein module allow the quantitative analysis of differences in the exchange activity under various conditions.
Collapse
Affiliation(s)
- Stefan Welti
- Structural and Computational Biology, Developmental Biology and Gene Expression Units, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | | | | | | | | |
Collapse
|
78
|
Abstract
Neurofibromin is a cytoplasmic protein that is predominantly expressed in neurons, Schwann cells, oligodendrocytes, astrocytes and leukocytes. It is encoded by the gene NF1, located on chromosome 17, at q11.2, and has different biochemical functions, including association to microtubules and participation in several signaling pathways. Alterations in this protein are responsible for a phacomatosis named neurofibromatosis type 1.
Collapse
Affiliation(s)
- A B Trovó-Marqui
- Departamento de Biologia, UNESP-Universidade Estadual Paulista, Brazil
| | | |
Collapse
|
79
|
Abstract
Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant disorders in humans. NF1 is caused by mutations in the NF1 gene which consists of 57 exons and encodes a GTPase activating protein (GAP), neurofibromin. To date, more than 640 different NF1 mutations have been identified and registered in the Human Gene Mutation Database (HGMD). In order to assess the NF1 mutational spectrum in Korean NF1 patients, we screened 23 unrelated Korean NF1 patients for mutations in the coding region and splice sites of the NF1 gene. We have identified 21 distinct NF1 mutations in 22 patients. The mutations included 10 single base substitutions (3 missense and 7 nonsense), 10 splice site mutations, and 1 single base deletion. Eight mutations have been previously identified and thirteen mutations were novel. The mutations are evenly distributed across exon 3 through intron 47 of the NF1 gene and no mutational hot spots were found. This analysis revealed a wide spectrum of NF1 mutations in Korean patients. A genotype- phenotype correlation analysis suggests that there is no clear relationship between specific NF1 mutations and clinical features of the disease.
Collapse
Affiliation(s)
- Seon-Yong Jeong
- Department of Medical Genetics, School of Medicine, Ajou University, Suwon, Korea
| | - Sang-Jin Park
- Department of Medical Genetics, School of Medicine, Ajou University, Suwon, Korea
| | - Hyon J. Kim
- Department of Medical Genetics, School of Medicine, Ajou University, Suwon, Korea
| |
Collapse
|
80
|
De Luca A, Bottillo I, Sarkozy A, Carta C, Neri C, Bellacchio E, Schirinzi A, Conti E, Zampino G, Battaglia A, Majore S, Rinaldi MM, Carella M, Marino B, Pizzuti A, Digilio MC, Tartaglia M, Dallapiccola B. NF1 gene mutations represent the major molecular event underlying neurofibromatosis-Noonan syndrome. Am J Hum Genet 2005; 77:1092-101. [PMID: 16380919 PMCID: PMC1285166 DOI: 10.1086/498454] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2005] [Accepted: 09/23/2005] [Indexed: 11/03/2022] Open
Abstract
Neurofibromatosis type 1 (NF1) demonstrates phenotypic overlap with Noonan syndrome (NS) in some patients, which results in the so-called neurofibromatosis-Noonan syndrome (NFNS). From a genetic point of view, NFNS is a poorly understood condition, and controversy remains as to whether it represents a variable manifestation of either NF1 or NS or is a distinct clinical entity. To answer this question, we screened a cohort with clinically well-characterized NFNS for mutations in the entire coding sequence of the NF1 and PTPN11 genes. Heterozygous NF1 defects were identified in 16 of the 17 unrelated subjects included in the study, which provides evidence that mutations in NF1 represent the major molecular event underlying this condition. Lesions included nonsense mutations, out-of-frame deletions, missense changes, small inframe deletions, and one large multiexon deletion. Remarkably, a high prevalence of inframe defects affecting exons 24 and 25, which encode a portion of the GAP-related domain of the protein, was observed. On the other hand, no defect in PTPN11 was observed, and no lesion affecting exons 11-27 of the NF1 gene was identified in 100 PTPN11 mutation-negative subjects with NS, which provides further evidence that NFNS and NS are genetically distinct disorders. These results support the view that NFNS represents a variant of NF1 and is caused by mutations of the NF1 gene, some of which have been demonstrated to cause classic NF1 in other individuals.
Collapse
Affiliation(s)
- Alessandro De Luca
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Irene Bottillo
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Anna Sarkozy
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Claudio Carta
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Cinzia Neri
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Emanuele Bellacchio
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Annalisa Schirinzi
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Emanuela Conti
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Giuseppe Zampino
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Agatino Battaglia
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Silvia Majore
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Maria M. Rinaldi
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Massimo Carella
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Bruno Marino
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Antonio Pizzuti
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Maria Cristina Digilio
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Marco Tartaglia
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| | - Bruno Dallapiccola
- CSS Hospital, IRCCS, San Giovanni Rotondo and CSS-Mendel Institute, Department of Experimental Medicine and Pathology and Section of Pediatric Cardiology, Department of Pediatrics, University “La Sapienza,” Dipartimento di Biologia Cellulare e Neuroscienze, Istituto Superiore di Sanità, Istituto di Clinica Pediatrica, Università Cattolica del Sacro Cuore, AO San Camillo-Forlanini, and Medical Genetics, Bambino Gesù Hospital, IRCCS, Rome; Stella Maris Scientific Research Institute, Calambrone, Pisa; Genetica Medica, Ospedale Cardarelli, Naples, Italy; and Department of Pediatrics, Mount Sinai School of Medicine, New York
| |
Collapse
|
81
|
Huang JW, Chen CL, Chuang NN. Trap RACK1 with Ras to mobilize Src signaling at syndecan-2/p120-GAP upon transformation with oncogenic ras. Biochem Biophys Res Commun 2005; 330:1087-94. [PMID: 15823555 DOI: 10.1016/j.bbrc.2005.02.189] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2005] [Indexed: 11/16/2022]
Abstract
HiTrap-syndecan-2/p120-GAP and HiTrap-syndecan-2/RACK1 affinity columns were applied to reveal that Src tyrosine kinase was highly expressed in BALB/3T3 cells transfected with plasmids pcDNA3.1-[S-ras(Q(61)K)] of shrimp Penaeus japonicus. Both columns were effective to isolate Src tyrosine kinase. The selective molecular affinity for Src was found to be stronger with HiTrap-syndecan-2/RACK1, as revealed with competitive RACK1 to dislodge Src from HiTrap-syndecan-2/p120-GAP. We thus challenged the syndecan-2/p120-GAP and syndecan-2/RACK1 with GTP-K(B)-Ras(Q(61)K). The reaction between RACK1 and syndecan-2 was sustained in the presence of mutant Ras proteins, but not the reaction between p120-GAP and syndecan-2. In the presence of syndecan-2, GTP-K(B)-Ras(Q(61)K) exhibited sufficient reactivity with p120-GAP to discontinue the reaction between p120-GAP and syndecan-2. But the interference of mutant Ras disappeared when Src tyrosine kinase was introduced to stabilize the syndecan-2/p120-GAP complex. On the other hand, in the absence of syndecan-2, GTP-K(B)-Ras(Q(61)K) was found to react with RACK1. The reaction between GTP-K(B)-Ras(Q(61)K) and RACK1 could provide a mechanism to deprive RACK1 for the organization of syndecan-2/RACK1 complex and to facilitate the formation of syndecan-2/p120-GAP complex, as well as to provide docking sites for Src signaling upon transformation with oncogenic ras.
Collapse
Affiliation(s)
- Jin-Wen Huang
- Institute of Zoology, National Taiwan University, Taipei, Taiwan
| | | | | |
Collapse
|
82
|
Chu LY, Chen YH, Chuang NN. Dimerize RACK1 upon transformation with oncogenic ras. Biochem Biophys Res Commun 2005; 330:474-82. [PMID: 15796907 DOI: 10.1016/j.bbrc.2005.03.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2005] [Indexed: 11/16/2022]
Abstract
From our previous studies, we learned that syndecan-2/p120-GAP complex provided docking site for Src to prosecute tyrosine kinase activity upon transformation with oncogenic ras. And, RACK1 protein was reactive with syndecan-2 to keep Src inactivated, but not when Ras was overexpressed. In the present study, we characterized the reaction between RACK1 protein and Ras. RACK1 was isolated from BALB/3T3 cells transfected with plasmids pcDNA3.1-[S-ras(Q61K)] of shrimp Penaeus japonicus and RACK1 was revealed to react with GTP-K(B)-Ras(Q61K), not GDP-K(B)-Ras(Q61K). This selective interaction between RACK1 and GTP-K(B)-Ras(Q61K) was further confirmed with RACK1 of human placenta and mouse RACK1-encoded fusion protein. We found that RACK1 was dimerized upon reaction with GTP-K(B)-Ras(Q61K), as well as with 14-3-3beta and geranylgeranyl pyrophosphate, as revealed by phosphorylation with Src tyrosine kinase. We reported the complex of RACK1/GTP-K(B)-Ras(Q61K) reacted selectively with p120-GAP. This interaction was sufficient to dissemble RACK1 into monomers, a preferred form to compete for the binding of syndecan-2. These data indicate that the reaction of GTP-K(B)-Ras(Q61K) with RACK1 in dimers may operate a mechanism to deplete RACK1 from reaction with syndecan-2 upon transformation by oncogenic ras and the RACK1/GTP-Ras complex may provide a route to react with p120-GAP and recycle monomeric RACK1 to syndecan-2.
Collapse
Affiliation(s)
- Ling-Yun Chu
- Institute of Zoology, National Taiwan University, Taipei, Taiwan
| | | | | |
Collapse
|
83
|
Huang JW, Chen CL, Chuang NN. P120-GAP associated with syndecan-2 to function as an active switch signal for Src upon transformation with oncogenic ras. Biochem Biophys Res Commun 2005; 329:855-62. [PMID: 15752734 DOI: 10.1016/j.bbrc.2005.02.045] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2005] [Indexed: 10/25/2022]
Abstract
BALB/3T3 cells transfected with plasmids pcDNA3.1-[S-ras(Q(61)K)] of shrimp Penaeus japonicus were applied to reveal a complex of p120-GAP/syndecan-2 being highly expressed upon transformation. Of interest, most of the p120-GAP/syndecan-2 complex was localized at caveolae, a membrane microdomain enriched with caveolin-1. To confirm the molecular interaction between syndecan-2 and p120-GAP, we further purified p120-GAP protein from mouse brains by using an affinity column of HiTrap-RACK1 and expressed mouse RACK1-encoded fusion protein and mouse syndecan-2-encoded fusion protein in bacteria. We report molecular affinities exist between p120-GAP and RACK1, syndecan-2 and RACK1 as well as p120-GAP and syndecan-2. The selective affinity between p120-GAP and syndecan-2 was found to be sufficient to detach RACK1. The p120-GAP/syndecan-2 complex was demonstrated to keep Src tyrosine kinase in an activated form. On the other hand, the syndecan-2/RACK1 complex was found to have Src in an inactivated form. These data indicate that the p120-GAP/syndecan-2 complex at caveolae could provide a docking site for Src to transmit tyrosine signaling, implying that syndecan-2/p120-GAP functions as a tumor promoter upon transformation with oncogenic ras of shrimp P. japonicus.
Collapse
Affiliation(s)
- Jin-Wen Huang
- Division of Biochemistry and Molecular Science, Institute of Zoology, Academia Sinica, Nankang, 11529 Taipei, Taiwan
| | | | | |
Collapse
|
84
|
Chautard H, Jacquet M, Schoentgen F, Bureaud N, Bénédetti H. Tfs1p, a member of the PEBP family, inhibits the Ira2p but not the Ira1p Ras GTPase-activating protein in Saccharomyces cerevisiae. EUKARYOTIC CELL 2004; 3:459-70. [PMID: 15075275 PMCID: PMC387632 DOI: 10.1128/ec.3.2.459-470.2004] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Ras proteins are guanine nucleotide-binding proteins that are highly conserved among eukaryotes. They are involved in signal transduction pathways and are tightly regulated by two sets of antagonistic proteins: GTPase-activating proteins (GAPs) inhibit Ras proteins, whereas guanine exchange factors activate them. In this work, we describe Tfs1p, the first physiological inhibitor of a Ras GAP, Ira2p, in Saccharomyces cerevisiae. TFS1 is a multicopy suppressor of the cdc25-1 mutation in yeast and corresponds to the so-called Ic CPY cytoplasmic inhibitor. Moreover, Tfs1p belongs to the phosphatidylethanolamine-binding protein (PEBP) family, one member of which is RKIP, a kinase and serine protease inhibitor and a metastasis inhibitor in prostate cancer. In this work, the results of (i) a two-hybrid screen of a yeast genomic library, (ii) glutathione S-transferase pulldown experiments, (iii) multicopy suppressor tests of cdc25-1 mutants, and (iv) stress resistance tests to evaluate the activation level of Ras demonstrate that Tfs1p interacts with and inhibits Ira2p. We further show that the conserved ligand-binding pocket of Tfs1-the hallmark of the PEBP family-is important for its inhibitory activity.
Collapse
Affiliation(s)
- Hélène Chautard
- Centre de Biophysique Moléculaire, Centre National de la Recherche Scientifique, UPR 4301, University of Orléans and INSERM, 45071 Orléans Cedex 2, France
| | | | | | | | | |
Collapse
|
85
|
Hishida T, Han YW, Fujimoto S, Iwasaki H, Shinagawa H. Direct evidence that a conserved arginine in RuvB AAA+ ATPase acts as an allosteric effector for the ATPase activity of the adjacent subunit in a hexamer. Proc Natl Acad Sci U S A 2004; 101:9573-7. [PMID: 15210950 PMCID: PMC470716 DOI: 10.1073/pnas.0403584101] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Escherichia coli RuvA and RuvB protein complex promotes branch migration of Holliday junctions during recombinational repair and homologous recombination and at stalled replication forks. The RuvB protein belongs to the AAA(+) (ATPase associated with various cellular activities) ATPase family and forms a hexameric ring in an ATP-dependent manner. Studies on the oligomeric AAA(+) class ATPases suggest that a conserved arginine residue is located in close proximity to the ATPase site of the adjacent subunit and plays an essential role during ATP hydrolysis. This study presents direct evidence that Arg-174 of RuvB allosterically stimulates the ATPase of the adjacent subunit in a RuvB hexamer. RuvBR174A shows a dominant negative phenotype for DNA repair in vivo and inhibits the branch migration catalyzed by wild-type RuvB. A dominant negative phenotype was also observed with RuvBK68A (Walker A mutation). RuvB K68A-R174A double mutant demonstrates a more severe dominant negative effect than the single mutants RuvB K68A or R174A. Moreover, although RuvB K68A and R174A are totally defective in ATPase activity, ATPase activity is restored when these two mutant proteins are mixed at a 1:1 ratio. These results suggest that each of the two mutants has distinct functional defects and that restoration of the ATPase activity is brought by complementary interaction between the mutant subunits in the heterohexamers. This study demonstrates that R174 plays an intermolecular catalytic role during ATP hydrolysis by RuvB. This role may be a general feature of the oligomeric AAA/AAA(+) ATPases.
Collapse
Affiliation(s)
- Takashi Hishida
- Department of Molecular Microbiology, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan
| | | | | | | | | |
Collapse
|
86
|
Vandenbroucke I, Van Oostveldt P, Coene E, De Paepe A, Messiaen L. Neurofibromin is actively transported to the nucleus. FEBS Lett 2004; 560:98-102. [PMID: 14988005 DOI: 10.1016/s0014-5793(04)00078-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2003] [Revised: 01/20/2004] [Accepted: 01/20/2004] [Indexed: 11/24/2022]
Abstract
Mutations in the neurofibromatosis type 1 (NF1) tumor suppressor gene predispose individuals to a variety of benign and malignant tumors. Many tumor suppressors 'shuttle' between the nucleus and the cytoplasm, thus regulating their function. By expressing different NF1 constructs in COS-7 cells (encompassing exons 28-49 and fused to the green fluorescent protein), we identified a functional nuclear localization signal (NLS) in exon 43. Mutation of the NLS completely abolishes the nuclear entry of the NF1-derivative fusion protein. A highly expressed splice variant that lacks this NLS controls the localization and hence the function of neurofibromin. The localization of neurofibromin in the nucleus may provide novel clues to unknown functions for NF1.
Collapse
Affiliation(s)
- Ina Vandenbroucke
- Centre for Medical Genetics, Ghent University Hospital, De Pintelaan 185-0K5, 9000 Ghent, Belgium
| | | | | | | | | |
Collapse
|
87
|
Trovó AB, Goloni-Bertollo EM, Mancini UM, Rahal P, Azevedo Jr. WFD, Tajara EH. Mutational analysis of the GAP-related domain of the neurofibromatosis type 1 gene in Brazilian NF1 patients. Genet Mol Biol 2004. [DOI: 10.1590/s1415-47572004000300003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
|
88
|
Yunoue S, Tokuo H, Fukunaga K, Feng L, Ozawa T, Nishi T, Kikuchi A, Hattori S, Kuratsu J, Saya H, Araki N. Neurofibromatosis type I tumor suppressor neurofibromin regulates neuronal differentiation via its GTPase-activating protein function toward Ras. J Biol Chem 2003; 278:26958-69. [PMID: 12730209 DOI: 10.1074/jbc.m209413200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Neurofibromin, the neurofibromatosis type 1 (NF1) gene product, contains a central domain homologous to a family of proteins known as Ras-GTPase-activating proteins (Ras-GAPs), which function as negative regulators of Ras. The loss of neurofibromin function has been thought to be implicated in the abnormal regulation of Ras in NF1-related pathogenesis. In this study, we found a novel role of neurofibromin in neuronal differentiation in conjunction with the regulation of Ras activity via its GAP-related domain (GRD) in neuronal cells. In PC12 cells, time-dependent increases in the GAP activity of cellular neurofibromin (NF1-GAP) were detected after NGF stimulation, which were correlated with the down-regulation of Ras activity during neurite elongation. Interestingly, the NF1-GAP increase was due to the induction of alternative splicing of NF1-GRD type I triggered by the NGF-induced Ras activation. Dominant-negative (DN) forms of NF1-GRD type I significantly inhibited the neurite extension of PC12 cells via regulation of the Ras state. NF1-GRD-DN also reduced axonal and dendritic branching/extension of rat embryonic hippocampal neurons. These results demonstrate that the mutual regulation of Ras and NF1-GAP is essential for normal neuronal differentiation and that abnormal regulation in neuronal cells may be implicated in NF1-related learning and memory disturbance.
Collapse
Affiliation(s)
- Shunji Yunoue
- Department of Tumor Genetics and Biology, Kumamoto University School of Medicine, Kumamoto 860-0811, Japan
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
89
|
Corral T, Jiménez M, Hernández-Muñoz I, Pérez de Castro I, Pellicer A. NF1 modulates the effects of ras oncogenes: Evidence of other NF1 function besides its GAP activity. J Cell Physiol 2003; 197:214-24. [PMID: 14502561 DOI: 10.1002/jcp.10349] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Neurofibromin (NF1) (the product of Nf1 gene) is a large cytosolic protein known as a negative regulator of Ras. A fragment of some 400 residues located at the center of the NF1 GAP-Related Domain (NF1-GRD) has strong identity with other molecules of the GAP family, which comprises, among others, the mammalian proteins NF1 and p120GAP, and the yeast proteins IRA1 and IRA2. GAP family members are known by their ability to promote the GTPase activity of Ras proteins, facilitating the transit of those proteins to their inactive state. Recent findings (Tong et al., 2002, Nat Neurosci 5:95-96) indicate that NF1 may be involved in the regulation of adenyl cyclase activity. Our results show that NF1-GRD cooperates with Ras in the anchorage-independent growth capacity of Ras-expressing fibroblasts, without affecting: (i) their ability to grow in low serum, (ii) their cellular adhesion capability, or (iii) the expression of key proteins involved in cell-cell and cell-matrix interactions. On the other hand, NF1 overexpression induces an increase in the expression levels of the focal adhesion kinase (FAK), and specific changes in the activation status of the mitogen-activated protein kinases (MAPKs). These results suggest the existence of a Ras-independent NF1-dependent pathway able to modify the levels of expression of FAK and the levels of activation of MAPKs. Because FAK and many proteins recently found to bind NF1 have a role in the cytoskeleton, this pathway may involve rearrangement of cytoskeletal components that facilitate anchorage independence.
Collapse
Affiliation(s)
- Teresa Corral
- Department of Pathology, New York University School of Medicine, New York, New York, USA
| | | | | | | | | |
Collapse
|
90
|
Ahmadian MR, Kiel C, Stege P, Scheffzek K. Structural fingerprints of the Ras-GTPase activating proteins neurofibromin and p120GAP. J Mol Biol 2003; 329:699-710. [PMID: 12787671 DOI: 10.1016/s0022-2836(03)00514-x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Ras specific GTPase activating proteins (GAPs), neurofibromin and p120GAP, bind GTP bound Ras and efficiently complement its active site. Here we present comparative data from mutations and fluorescence-based assays of the catalytic domains of both RasGAPs and interpret them using the crystal structures. Three prominent regions in RasGAPs, the arginine-finger loop, the phenylalanine-leucine-arginine (FLR) region and alpha7/variable loop contain structural fingerprints governing the GAP function. The finger loop is crucial for the stabilization of the transition state of the GTPase reaction. This function is controlled by residues proximal to the catalytic arginine, which are strikingly different between the two RasGAPs. These residues specifically determine the orientation and therefore the positioning of the arginine finger in the Ras active site. The invariant FLR region, a hallmark for RasGAPs, indirectly contributes to GTPase stimulation by forming a scaffold, which stabilizes Ras switch regions. We show that a long hydrophobic side-chain in the FLR region is crucial for this function. The alpha7/variable loop uses several conserved residues including two lysine residues, which are involved in numerous interactions with the switch I region of Ras. This region determines the specificity of the Ras-RasGAP interaction.
Collapse
Affiliation(s)
- Mohammad Reza Ahmadian
- Department Structural Biology, Max-Planck-Institute for Molecular Physiology, Otto-Hahn-Strasse 11, 44227, Dortmund, Germany
| | | | | | | |
Collapse
|
91
|
Bernards A. GAPs galore! A survey of putative Ras superfamily GTPase activating proteins in man and Drosophila. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1603:47-82. [PMID: 12618308 DOI: 10.1016/s0304-419x(02)00082-3] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Typical members of the Ras superfamily of small monomeric GTP-binding proteins function as regulators of diverse processes by cycling between biologically active GTP- and inactive GDP-bound conformations. Proteins that control this cycling include guanine nucleotide exchange factors or GEFs, which activate Ras superfamily members by catalyzing GTP for GDP exchange, and GTPase activating proteins or GAPs, which accelerate the low intrinsic GTP hydrolysis rate of typical Ras superfamily members, thus causing their inactivation. Two among the latter class of proteins have been implicated in common genetic disorders associated with an increased cancer risk, neurofibromatosis-1, and tuberous sclerosis. To facilitate genetic analysis, I surveyed Drosophila and human sequence databases for genes predicting proteins related to GAPs for Ras superfamily members. Remarkably, close to 0.5% of genes in both species (173 human and 64 Drosophila genes) predict proteins related to GAPs for Arf, Rab, Ran, Rap, Ras, Rho, and Sar family GTPases. Information on these genes has been entered into a pair of relational databases, which can be used to identify evolutionary conserved proteins that are likely to serve basic biological functions, and which can be updated when definitive information on the coding potential of both genomes becomes available.
Collapse
Affiliation(s)
- André Bernards
- Massachusetts General Hospital Cancer Center, Building 149, 13th Street, Charlestown, MA 02129-2000, USA.
| |
Collapse
|
92
|
Donovan S, Shannon KM, Bollag G. GTPase activating proteins: critical regulators of intracellular signaling. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1602:23-45. [PMID: 11960693 DOI: 10.1016/s0304-419x(01)00041-5] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Shane Donovan
- Department of Pediatrics and Comprehensive Cancer Center, 513 Parnassus Ave., Room HSE-302, University of California, San Francisco, CA 94143-0519, USA
| | | | | |
Collapse
|
93
|
Nokelainen P, Flint J. Genetic effects on human cognition: lessons from the study of mental retardation syndromes. J Neurol Neurosurg Psychiatry 2002; 72:287-96. [PMID: 11861682 PMCID: PMC1737778 DOI: 10.1136/jnnp.72.3.287] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The molecular basis of human cognition is still poorly understood, but recent advances in finding genetic mutations that result in cognitive impairment may provide insights into the neurobiology of cognitive function. Here we review the progress that has been made so far and assess what has been learnt from this work on the relation between genes and cognitive processes. We review evidence that the pathway from genetic lesion to cognitive impairment can be dissected, that some genetic effects on cognition are relatively direct and we argue that the study of mental retardation syndromes is giving us new clues about the biological bases of cognition.
Collapse
Affiliation(s)
- P Nokelainen
- Wellcome Trust Centre for Human Genetics, Roosevelt Drive, Oxford OX3 7BN, UK
| | | |
Collapse
|
94
|
Song YH, Marx A, Müller J, Woehlke G, Schliwa M, Krebs A, Hoenger A, Mandelkow E. Structure of a fast kinesin: implications for ATPase mechanism and interactions with microtubules. EMBO J 2001; 20:6213-25. [PMID: 11707393 PMCID: PMC125725 DOI: 10.1093/emboj/20.22.6213] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We determined the crystal structure of the motor domain of the fast fungal kinesin from Neurospora crassa (NcKin). The structure has several unique features. (i) Loop 11 in the switch 2 region is ordered and enables one to describe the complete nucleotide-binding pocket, including three inter-switch salt bridges between switch 1 and 2. (ii) Loop 9 in the switch 1 region bends outwards, making the nucleotide-binding pocket very wide. The displacement in switch 1 resembles that of the G-protein ras complexed with its guanosine nucleotide exchange factor. (iii) Loop 5 in the entrance to the nucleotide-binding pocket is remarkably long and interacts with the ribose of ATP. (iv) The linker and neck region is not well defined, indicating that it is mobile. (v) Image reconstructions of ice-embedded microtubules decorated with NcKin show that it interacts with several tubulin subunits, including a central beta-tubulin monomer and the two flanking alpha-tubulin monomers within the microtubule protofilament. Comparison of NcKin with other kinesins, myosin and G-proteins suggests that the rate-limiting step of ADP release is accelerated in the fungal kinesin and accounts for the unusually high velocity and ATPase activity.
Collapse
Affiliation(s)
- Y.-H. Song
- Max-Planck Unit for Structural Molecular Biology, D-22607 Hamburg,
Department of Cell Biology, Ludwig-Maximilians-University, D-80336 München and EMBL, D-69117 Heidelberg, Germany Corresponding authors e-mail: or
| | | | | | - G. Woehlke
- Max-Planck Unit for Structural Molecular Biology, D-22607 Hamburg,
Department of Cell Biology, Ludwig-Maximilians-University, D-80336 München and EMBL, D-69117 Heidelberg, Germany Corresponding authors e-mail: or
| | - M. Schliwa
- Max-Planck Unit for Structural Molecular Biology, D-22607 Hamburg,
Department of Cell Biology, Ludwig-Maximilians-University, D-80336 München and EMBL, D-69117 Heidelberg, Germany Corresponding authors e-mail: or
| | - A. Krebs
- Max-Planck Unit for Structural Molecular Biology, D-22607 Hamburg,
Department of Cell Biology, Ludwig-Maximilians-University, D-80336 München and EMBL, D-69117 Heidelberg, Germany Corresponding authors e-mail: or
| | - A. Hoenger
- Max-Planck Unit for Structural Molecular Biology, D-22607 Hamburg,
Department of Cell Biology, Ludwig-Maximilians-University, D-80336 München and EMBL, D-69117 Heidelberg, Germany Corresponding authors e-mail: or
| | - E. Mandelkow
- Max-Planck Unit for Structural Molecular Biology, D-22607 Hamburg,
Department of Cell Biology, Ludwig-Maximilians-University, D-80336 München and EMBL, D-69117 Heidelberg, Germany Corresponding authors e-mail: or
| |
Collapse
|
95
|
|
96
|
Chang KC, Chuang NN. GTPase stimulation in shrimp Ras(Q(61)K) with geranylgeranyl pyrophosphate but not mammalian GAP. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 2001; 290:642-51. [PMID: 11748613 DOI: 10.1002/jez.1115] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
BALB/3T3 cells were transformed by transfection with DNA encoding the mutated ras(Q(61)K) from shrimp Penaeus japonicus (Huang et al., 2000). The GTPase-activating protein (GAP) in the cytosol fraction was significantly expressed and degraded, compared to untransformed cells on the western blot. To understand this in more detail, the interaction of the bacterially expressed shrimp Ras (S-Ras) with GAP was investigated using GAP purified from mouse brains. SDS-polyacrylamide gel electrophoresis revealed the monomers of the purified GAP to have a relative mass of 65,000. Since the purified GAP was bound to the Ras conjugated affinity sepharose column with high affinity and its GTP hydolysis activity upon binding with tubulin was suppressed, the purified enzyme was concluded to be neurofibromin-like. The purified GAP enhanced the intrinsic GTPase activity of the S-Ras, to convert it into the inactive GDP-bound form, in agreement with findings for GTP-bound K(B)-Ras in vitro. To compare the effects between isoprenoids and GAP on the GTP-hydrolysis of Ras, we applied the GTP-locked shrimp mutant S-Ras(Q(61)K) and GTP-locked rat mutant K(B)-ras(Q(61)K). Radioassay studies showed that geranylgeranyl pyrophosphate at microg level catalyzed the GTP hydrolysis of S-Ras(Q(61)K) and K(B)-ras(Q(61)K) competently, but not farnesyl pyrophosphate or the purified GAP. The present study provides the view that the geranylgeranyl pyrophosphate at carboxyl terminal CAAX assists GTP hydrolysis to Ras proteins probably in a manner similar to the substrate assisted catalysis in GTPase mechanism.
Collapse
Affiliation(s)
- K C Chang
- Division of Biochemistry and Molecular Sciences, Institute of Zoology, Academia Sinica, Nankang, Taipei, Taiwan 11529
| | | |
Collapse
|
97
|
te Biesebeke R, Krab IM, Parmeggiani A. The arginine finger loop of yeast and human GAP is a determinant for the specificity toward Ras GTPase. Biochemistry 2001; 40:7474-9. [PMID: 11412100 DOI: 10.1021/bi010027a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this work, we have studied the role of the arginine finger region in determining the specificity of the GTPase activating proteins (GAPs) Saccharomyces cerevisiae Ira2p and human p120-GAP toward yeast Ras2p and human Ha-Ras p21. It is known that p120-GAP can enhance both Ras2p and Ha-Ras GTPase activities, whereas Ira2p is strictly specific for Ras2p and fails to activate Ha-Ras GTPase. Substitution in Ira2p of the arginine following the arginine finger with alanine, the residue found in the corresponding position of p120-GAP, or by glycine as found in neurofibromin, evokes a low but significant stimulation of Ha-Ras GTPase. The stimulatory activity of Ira2p on Ha-Ras increased by substituting segments of the finger loop region with p120-GAP residues, especially with the six residues forming the tip of the arginine loop. In p120-GAP, substitution of the entire finger loop with the corresponding region of Ira2p led to a construct completely inactive on Ha-Ras GTPase but active on yeast Ras2p GTPase. Analysis of these results and modeling of Ira2p.Ras complexes emphasize the importance of the finger loop region not only for the catalytic activity but also as a structural determinant involved in the specificity of GAPs toward Ras proteins from different organisms.
Collapse
Affiliation(s)
- R te Biesebeke
- Groupe de Biophysique-Equipe 2, Ecole Polytechnique, F-91128 Palaiseau Cedex, France
| | | | | |
Collapse
|
98
|
Abstract
The importance of genetic influences on cognitive disability has been recognized for a long time, but molecular analysis has only recently begun to yield insights into the pathogenesis of this common and disabling condition. The availability of genome sequences has enabled the characterization of the chromosomal deletions and trisomies that result in cognitive disability, and mutations in rare single-gene conditions are being discovered. The molecular pathology of cognitive disability is turning out to be as heterogeneous as the condition itself, with unexpected complexities even in apparently simple gene-deletion syndromes. One remarkable finding from studies on X-linked mental retardation is that mutations in different small guanosine triphosphate (GTP)-binding proteins result in cognitive disability without other somatic features. Advances are also being made in cognitive disability with polygenic origins, such as dyslexia and autism. However, the genetic basis of mild intellectual disability has yet to be satisfactorily explained.
Collapse
|
99
|
Hiatt KK, Ingram DA, Zhang Y, Bollag G, Clapp DW. Neurofibromin GTPase-activating protein-related domains restore normal growth in Nf1-/- cells. J Biol Chem 2001; 276:7240-5. [PMID: 11080503 DOI: 10.1074/jbc.m009202200] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Members of the Ras superfamily of signaling proteins modulate fundamental cellular processes by cycling between an active GTP-bound conformation and an inactive GDP-bound form. Neurofibromin, the protein product of the NF1 tumor suppressor gene, and p120GAP are GTPase-activating proteins (GAPs) for p21(Ras) (Ras) and negatively regulate output by accelerating GTP hydrolysis on Ras. Neurofibromin and p120GAP differ markedly outside of their conserved GAP-related domains (GRDs), and it is therefore unknown if the respective GRDs contribute functional specificity. To address this question, we expressed the GRDs of neurofibromin and p120GAP in primary cells from Nf1 mutant mice in vitro and in vivo. Here we show that expression of neurofibromin GRD, but not the p120GAP GRD, restores normal growth and cytokine signaling in three lineages of primary Nf1-deficient cells that have been implicated in the pathogenesis of neurofibromatosis type 1 (NF1). Furthermore, utilizing a GAP-inactive mutant NF1 GRD identified in a family with NF1, we demonstrate that growth restoration is a function of NF1 GRD GAP activity on p21(Ras). Thus, the GRDs of neurofibromin and p120GAP specify nonoverlapping functions in multiple primary cell types.
Collapse
Affiliation(s)
- K K Hiatt
- Herman B Wells Center for Pediatric Research, Departments of Microbiology/Immunology and Pediatrics, Indiana University School of Medicine, Indianapolis 46202, USA
| | | | | | | | | |
Collapse
|
100
|
Flint J. Genetic basis of cognitive disability. DIALOGUES IN CLINICAL NEUROSCIENCE 2001; 3:37-46. [PMID: 22034445 PMCID: PMC3181642] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 04/05/2024]
Abstract
The importance of genetic influences on cognitive disability has been recognized for a long time, but molecular analysis has only recently begun to yield insights into the pathogenesis of this common and disabling condition. The availability of genome sequences has enabled the characterization of the chromosomal deletions and trisomies that result in cognitive disability, and mutations in rare single-gene conditions are being discovered. The molecular pathology of cognitive disability is turning out to be as heterogeneous as the condition itself, with unexpected complexities even in apparently simple gene-deletion syndromes. One remarkable finding from studies on X-linked mental retardation is that mutations in different small guanosine triphosphate (GTP)-binding proteins result in cognitive disability without other somatic features. Advances are also being made in cognitive disability with polygenic origins, such as dyslexia and autism. However, the genetic basis of mild intellectual disability has yet to be satisfactorily explained.
Collapse
|