Gtpases in Biology I

ISBN-13: 9783642782695 / Angielski / Miękka / 2012 / 697 str.

K. Aktories; D. L. Altschuler; M. W. Anderson

Opis

Recent advances in molecular biology have shown GTPases and phosphoproteins to be the paramount molecular switches utilized intracellularly in biological systems. The origins of the GTPase switch appear to be almost as ancient as life itself, and through evolution nature has adapted this switch to a variety of purposes. In this two-volume work a broad survey of the major classes of GTPases is presented. The role of GTPases in ensuring accuracy during protein translation, a new look at the trimeric G-protein cycle, the molecular function of ARF in vesicle coating, the emerging role of the dynamin family in vesicle transfer, GTPases which activate GTPases during nascent protein translocation, and the many roles of ras-related proteins in growth, cytoskeletal polymerization, and vesicle transfer, are all described in 80 chapters by the leading authorities in their fields. Both detailed knowledge of specific systems or proteins and general principles of structure and function are offered. Much of this information has never been published before. At the rate the extended family of GTPases is growing it becomes increasingly unlikely that we will again get it to sit for a group portrait such as this. Therefore, the volume has the chance to become the reference work for GTPases.

Spis treści

Section I: Biological Importance of GTPase-Driven Switches.- 1 GTPases Everywhere!.- A. Introduction.- B. The GTPase Cycle and the Molecular Switch.- C. Structure of the GTPase Switch.- D. Primary Structures Identify GTPases with Related Functions.- E. Uses of the GTPase Switch: Stoichiometric Activation.- F. Uses of the GTPase Switch: Assembling a Complex.- G. Other Potential Uses of the GTPase Switch.- H. Cascades of GTPases.- I. Perspectives.- References.- 2 Proofreading in the Elongation Cycle of Protein Synthesis.- A. Introduction.- B. General Concepts.- I. Specificity.- II. Proofreading.- C. Parameters of Protein Biosynthesis.- D. EF-Tu-Dependent Kinetic Proofreading.- E. EF-Tu-Independent Error Correction Mechanisms.- I. Peptidyl Transfer.- II. EF-G-Dependent Translocation.- III. Allosteric Linkage Between A and E Sites.- F. Summary.- References.- 3 A New Look at Receptor-Mediated Activation of a G-Protein.- References.- 4 Small GTPases and Vesicle Trafficking: Sec4p and its Interaction with Up- and Downstream Elements.- A. Introduction.- B. The Sec4 Cycle.- I. A Cycle of Sec4 Localization.- II. Intrinsic Properties of Sec4.- III. GTP Binding and Membrane Attachment Are Essential for Sec4 function.- IV. GTP Hydrolysis Is Important for Sec4 function.- C. Accessory Proteins in the Sec4 Cycle.- I. A Specific Sec4 GAP Is Present in Yeast and Mammalian Cells.- II. GDI from Bovine Brain and Yeast Solubilizes Sec4 in a Nucleotide-Specific Fashion.- III. Suppressors from Yeast and Rat Brain Encode Nucleotide Exchange Proteins.- D. A Potential Downstream Effector of Sec4 Function: The Sec8/Secl5 Complex.- References.- 5 Cytoskeletal Assembly: The Actin and Tubulin Nucleotidases.- A. Introduction.- B. The Nucleotidase Cycle in the Polymerization of Actin and Tubulin.- C. Elementary Steps in NTP Hydrolysis on Actin Filaments and Microtubules: The Regulation of Polymer Assembly.- D. Nucleotide and Metal Ion Binding to Actin and Tubulin.- E. Probing the Nucleotidase Mechanism of Actin and Tubulin using AlF4? and BeF3?, H2O.- F. Conclusions.- References.- 6 Dynamin, A Microtubule-Activated GTPase Involved in Endocytosis.- A. Introduction.- B. Structure and Enzymatic Properties.- C. The Drosophila Shibire Gene.- D. Transfection of Dynamin into Cultured Mammalian Cells.- References.- 7 Transmembrane Protein Translocation: Signal Recognition Particle and Its Receptor in the Endoplasmic Reticulum.- A. Introduction.- B. The Signal Recognition Particle and Its Receptor.- C. Protein Translocation Across the Rough Endoplasmic Reticulum Requires GTP.- D. Binding and Hydrolysis of Guanine Ribonucleotides by Signal Recognition Particle and Its Receptor.- E. Site-Directed Mutagenesis of SR?.- F. The Sorting and Targeting Functions of Signal Recognition Particle are GTP Independent.- G. Current Models for GTP Function During Protein Translocation.- References.- 8 GTPases and Actin as Targets for Bacterial Toxins.- A. Introduction.- B. General Features of ADP-Ribosylating Toxins.- C. ADP-Ribosylation of Elongation Factor 2 by Diphtheria Toxin and Pseudomonas aeruginosa Exotoxin A.- I. Introduction.- II. Diphtheria Toxin.- III. Pseudomonas aeruginosa Exotoxin A.- IV. Functional Consequences of the ADP-Ribosylation of Elongation Factor 2.- D. ADP-Ribosylation of G-Proteins.- I. Introduction.- II. Cholera Toxin.- III. Heat-Labile E. coli Enterotoxins.- IV. Functional Consequences of the ADP-Ribosylation of G-Proteins by Cholera- and Heat-Labile E. coli Enterotoxins.- V. Pertussis Toxin.- VI. ADP-Ribosylation of Gi Go, and Gt by Pertussis Toxin.- E. ADP-Ribosylation of Small GTPases.- I. Introduction.- II. C3-Like ADP-Ribosyltransferases.- III. Functional Consequences of the ADP-Ribosylation of Rho Proteins.- IV. ADP-Ribosylation of Small GTPases by Pseudomonas aeruginosa Exoenzyme S.- F. ADP-Ribosylation of Actin.- I. Introduction.- II. Clostridium botulinum C2 Toxin.- III. Other Actin-ADP-Ribosylating Toxins.- IV. Functional Consequences of the ADP-Ribosylation of Actin.- G. Perspectives.- References.- Section II. Structure of the GTPase Switches.- 9 Eukaryotic Translation Factors Which Bind and Hydrolyze GTP.- A. GTPase Factors.- B. Consensus Sequences of GTPases Factors.- C. Evolution of EF-1?.- D. The EF-Tu Family.- E. Structures of the EF-Tu Family.- References.- 10 Heterotrimeric G-Proteins: ?, ?, and ? Subunits.- A. Introduction.- B. Mammalian G-Proteins.- I. ? Subunits.- 1. Isolation of cDNAs and Genomic DNAs.- a) Gs?.- b) Gi?.- c) Go?.- d) Gt? and Ggust?.- e) Gz?.- f) Gq? and G12?.- 2. Comparison of the Amino Acid Sequences.- a) P Region.- b) G? Region.- c) G Region.- d) G? Region.- e) Cholera Toxin ADP-Ribosylation Site.- 3. Sequence Conservation.- 4. Evolutionary Tree.- II. ? ? Subunits.- C. G-Proteins in Lower Eukaryotes.- I. G-Proteins from Saccharomyces cerevisiae.- 1. Two ? Subunits, GPA1 and GPA2.- 2. ? and ? Subunits.- II. G-Proteins from Schizosaccharomyces pombe.- III. G-Proteins from Caenorhabditis elegans.- IV. G-Proteins from Plants.- References.- 11 Molecular Diversity in Signal Transducing G-Proteins.- A. The ? Subunits.- I. Molecular Diversity.- II. ? Subunit Functions.- B. The ? ? Dimers.- References.- 12 Structural Conservation of Ras-Related Proteins and Its Functional Implications.- A. Introduction: The Discovery of Ras and Ras-Related Genes.- B. Sequence Comparisons.- I. The N-Terminal Extension.- II. The Phosphate-Binding Part.- III. The Guanine-Binding Part.- IV. The C-Terminal Extension.- V. The CaaX Motif.- C. Evolutionary Relationships.- I. Construction of a Homology Tree.- II. Insertions and Deletions.- III. Estimation of the Number of Ras-Related Proteins in Mammals.- D. Discussion.- I. Internal Residues.- II. External Residues and Potential Targets for Interacting Proteins.- III. Relation to Other GTPase Families.- IV. Is There a Conserved Functional Mechanism for All Ras-Related Proteins?.- References.- 13 Conformational Switch and Structural Basis for Oncogenic Mutations of Ras Proteins.- A. Introduction.- B. Conformational Switch.- I. Conformational Differences Between GDP- and GTP-Bound Ras Proteins: Switch I and II Regions.- II. Conformational Domino Effect and Frozen Dynamic States.- III. Small Conformational Changes in the Phosphate-Binding Loop, L1.- C. Structural Basis for Oncogenic Mutations.- I. Mutations at Gln-61 and the Stabilization of the Transition State of the ?-Phosphate of GTP.- II. Mutations at Gly-12 and the Stabilization of the Transition State of the ?-Phosphate of GTP.- III. Residues 12 and 13 Form a Type II ?-Turn for Phosphate Binding.- IV. Mutation at Ala-59 and Switch II Conformation.- D. Discussion.- References.- 14 Structural and Mechanistic Aspects of the GTPase Reaction of H-ras p21.- A. Introduction.- B. The Structure of the p21-Triphosphate State.- C. The Structure and Biochemistry of p21 Mutants.- D. The Kinetic Mechanism of the GTPase Reaction.- E. The Kinetic Mechanism of the GAP-stimulated GTPase.- F. GTPase Mechanism.- G. Arguments For and Against the Proposed Mechanism.- H. Role of GAP in the Chemical Mechanism.- I. Conclusion.- References.- 15 Analysis of Ras Structure and Dynamics by Nuclear Magnetic Resonance.- A. Introduction.- B. NMR Studies of Proteins.- I. NMR Structure Determination.- 1. NMR Methods: Larger Proteins.- 2. NMR Resonance Assignments: Application to Ras.- 3. Secondary Structure Determination: Application to Ras.- 4. Tertiary Structure and Structure Refinement.- II. Comparison of Solution and Crystal Structures.- 1. Computer Simulation: Ras·GMPPNP Solution Structure.- 2. Protein Dynamics.- C. Comparison of Full length and Truncated Ras Proteins.- I. Protein Stability: Sample Preparation.- II. Chemical Shift Differences.- III. Selective Isotope Enrichment Studies: Site Specific Probes.- 1. Identification of C-Terminal Peaks.- 2. Internal Dynamics.- 3. Comparison of Intact Ras·GDP and Ras·GMPPCP.- D. Comparison of Ras·GTP, Ras·GTP?S, Ras·GMPPCP and Ras·GDP.- I. Chemical Shift Differences.- E. Kinetic Measurements.- I. Kinetic and Fluorescence Studies.- II. 31P NMR: Ras·GTP Hydrolysis.- III. [1H-15N]-Edited NMR Spectroscopy: GTP Hydrolysis.- F. Conclusion.- References.- 16 Molecular Dynamics Studies of H-ras p21-GTP.- A. Introduction.- B. Methods.- C. Results and Discussion.- I. General Features of the Wild-Type Simulations.- 1. RMS.- 2. Protein-GTP Contacts.- 3. Secondary Structure.- II. Mechanism of Hydrolysis.- References.- Section III: Small Ras — Related GTPases.- A. Control of Growth and Differentiation by the Ras Family.- 17 The Discovery of Ras and Its Biological Importance.- References.- 18 Oncogenic Activation of ras Proteins.- A. Introduction.- B. Oncogenic Versions of Cellular ras Genes Detected in Tumor Cells.- I. Biological Detection of Activating ras Genes.- II. Direct Detection of ras Mutations in Tumor DNA and RNA.- III. Polymerase Chain Reaction Based Approaches to Screening Tumors.- C. Frequent Occurrence of Mutated ras Genes in Human Tumors.- D. ras Activation is Associated with Experimentally Induced Rodent Tumors.- E. Biological Activities of Oncogenic ras Proteins.- I. Malignant Transformation of Established Rodent Fibroblast Cell Lines.- II. ras Requires Cooperation with Other Oncogenes for Transformation of Primary Cells.- III. Induction of Differentiation and Growth Inhibition by Oncogenic ras.- IV. Transgenic Mouse Studies Establish ras Oncogenicity.- F. Structural and Biochemical Consequences of Oncogenic Mutations.- I. Activating Mutations at Residues 12, 13, or 61 Promote Active, GTP-Complexed ras Formation.- II. Other Activating Mutations Also Perturb the ras GDP-GTP Cycle.- G. Clinical Implications of Oncogenic ras for Diagnosis and Treatment.- I. Diagnostic and Prognostic Applications of ras Mutations.- II. Protein Prenylation: Oncogenic ras Proteins as Targets of Therapy.- H. Future Questions.- References.- 19 Dominant Inhibitory Ras Mutants: Tools for Elucidating Ras function.- A. Introduction.- B. Mechanism of Inhibitory Action.- C. Defining Biochemical Pathways Dependent upon Ras function.- D. Some Surprises Revealed by Dominant Inhibitory Ras Mutants.- E. Conclusions.- References.- 20 The Involvement of Cellular ras in Proliferative Signaling.- A. Introduction.- B. The Relationship Between Tyrosine Kinase Oncogenes and Cellular ras.- I. Neutralizing Anti-ras Antibody.- II. Inhibition in the Late G1 Phase of the Cell Cycle.- III. ras and Other Oncogene Classes.- C. A Model for Proliferative Signal Transduction.- I. Other Studies Which Support the Model.- D. Lipids and the Control of ras Activity.- I. Dependence of Lipid Mitogens upon ras.- II. Biochemical Effects of Lipids upon ras.- E. Biochemical Analyses of the Interaction Between ras and Lipids.- I. Lipids and ras-Related Proteins.- II. Neurofibromin and Lipid Inhibition.- III. Production of GAP-Inhibitory Lipids by Mitogen Stimulation.- IV. Physical Association Between GAP and Lipids.- V. Mutational Analysis of ras and the Lipid Inhibitory Phenotype.- VI. Other Studies of Lipids and GAP Activity.- VII. Tyrosine Kinases and Lipid Metabolism.- VIII. Model for the Control of Proliferation at the Level of ras Activity.- F. Cellular Factors Affecting ras Activity.- I. N17 ras Interferes with the Activation of Cellular ras.- II. RAST is Preferentially Inhibitory for Oncogenic ras.- III. Model for Inhibition of ras Activity by Dominant Inhibitory Mutants.- IV. Biochemical Support for the Idea that RAST Binds an Effector.- G. Summary.- References.- 21 Regulation of Ras-Interacting Proteins in Saccharomyces cerevisiae.- A. Introduction.- B. Regulation of Ras Activity by Guanine Nucleotides.- I. Biochemical Properties of Ras.- II. The CDC25 Gene.- III. IRA1 and IRA2 Genes.- C. Regulation of Adenylyl Cyclase by Ras.- D. Domains of Ras Interacting with Other Proteins.- E. Conclusions.- References.- 22 Lipid Modifications of Proteins in the Ras Superfamily.- A. Background.- B. Farnesylation.- I. Farnesyl-Protein Transferase.- II. Function of Farnesylation.- C. Geranylgeranylation.- D. Other Modifications.- I. Proteolysis.- II. Methylation.- III. Palmitoylation.- E. Conclusions.- References.- 23 GTPase Activating Proteins.- A. Introduction.- B. GTPase Activating Proteins for ras p21 Proteins.- I. GTPase Activating Proteins in Saccharomyces cerevisiae.- II. GTPase Activating Proteins in Schizosaccharomyces pombe.- III. GTPase Activating Proteins in Drosophila melanogaster.- IV. GTPase Activating Proteins in Mammalian Cells.- C. GTPase Activating Proteins for rap p21’s.- D. GTPase Activating Proteins for rho-Like Proteins.- E. GTPase Activating Proteins for other small GTPases.- F. Concluding Remarks.- References.- 24 Guanine Nucleotide Dissociation Stimulators.- A. Introduction.- B. Possible Mechanisms for conversion to the GTP-Bound State.- C. Nonspecific Guanine Nucleotide Dissociation Stimulators.- D. Ras-Specific Guanine Nucleotide Dissociation Stimulators.- I. Mammalian Guanine Nucleotide Dissociation Stimulators.- II. Yeast Guanine Nucleotide Dissociation Stimulators: CDC25, SCD25 and ste6.- III. A Ras-Specific Guanine Nucleotide Dissociation Stimulator in Drosophila: SOS.- E. RAB3-Specific Guanine Nucleotide Dissociation Stimulator.- F. Other Guanine Nucleotide Dissociation Stimulators.- G. Conclusions.- References.- 25 The Biology of Rap.- A. Introduction.- B. Cloning/Isolation of Rap(s).- C. Posttranslational Modification of Rap Proteins.- I. Isoprenylation.- II. Phosphorylation.- D. Rap1 Regulatory Proteins.- I. GTPase Activating Proteins.- II. GDP/GTP Dissociation Stimulator.- E. Biological Activities of Rap1 Protein.- I. Antagonism of Ras by Rap1.- II. Interaction of Rap1A with the Phagocyte Reduced Nicotinamide Adenine Dinucleotide Phosphate Oxidase.- F. Conclusion.- References.- B. Vesicle Transfer/Vesicle Fusion.- 26 GTPases and Interacting Elements in Vesicle Budding and Targeting in Yeast.- A. Introduction.- B. Isolation and Characterization of Secretion Defective Yeast Strains.- C. Biochemical Analysis of Protein Transport from the Endoplasmic Reticulum to the Golgi Apparatus.- D. Sar1p Function in Vesicle Formation from the Endoplasmic Reticulum.- E. Concluding Remarks.- References.- 27 Ypt Proteins in Yeast and Their Role in Intracellular Transport.- A. Introduction.- B. Ypt Proteins in Saccharomyces derevisiae.- I. Ypt1 Protein.- II. Sec4 Protein.- III. Ypt3, Ypt6 and Ypt7 Proteins.- C. Ypt Protein Structure.- I. Nucleotide Binding.- II. Effector Region.- III. C Terminus.- D. GTPase Activating Proteins for YPT Family Members.- E. Summary.- References.- 28 Compartmentalization of rab Proteins in Mammalian Cells.- A. Subcellular Compartmentalization and Membrane Traffic.- I. Membrane Trafficking.- 1. Indications for a Role of Sec4/Ypt1/rab GTPases.- B. Localization of rab Proteins on Subcellular Compartments.- I. The rab Proteins Associated with the Biosynthetic Route.- 1. Endoplasmic Reticulum and Golgi Apparatus.- 2. The rab3a Protein on Regulated Exocytic Vesicles.- II. The rab Proteins on Endocytic Compartments.- 1. The rab5 and rab4 Proteins on Early Endosomes.- 2. The rab Proteins on Late Endocytic Compartments.- III. The Molecular Basis of rab Compartmentalization.- 1. The C-Terminal Modifications.- 2. Role of the C-Terminal Variable Region.- C. The Function of rab Proteins in Membrane Trafficking.- I. The Present Model for rab function.- II. Experimental Evidence for rab Function in Membrane Trafficking.- 1. The rab1, rab2, and rab9 Proteins are Involved in Transport Steps on the Biosynthetic Route.- 2. The rab3a Protein and Regulated Secretion.- 3. Functional Studies on rab5 and rab4.- 4. Conclusion from the Functional Data.- D. The Novel rab Proteins.- I. Why Clone More rab Sequences?.- II. Subcellular Localization.- 1. Novel Proteins on the Biosynthetic Pathway.- 2. Novel Proteins on Early Endocytic Compartments.- III. Epithelial-Specific rab Proteins?.- E. Conclusion.- References.- 29 GTPases in Transport Between Late Endosomes and the Trans Golgi Network.- A. Small GTPases in Membrane Traffic.- B. In Vitro Assays to Analyze the Role of GTP in Membrane Traffic.- I. Introduction.- II. Transport of Mannose 6-Phosphate Receptors From Late Endosomes to the trans Golgi Network In Vitro.- III. GTP?S Inhibits Endosome-to-TGN Transport In Vitro.- IV. A GTP?S-Sensitive Transport Component Requires Late Endosomes for Its Activity.- C. Role of rab Proteins in Endosome to trans Golgi Network Transport.- D. A Model for rab Protein function.- I. Recruitment of rab Proteins onto Nascent Transport Vesicles.- 1. Newly Synthesized rab Proteins are Cytosolic.- 2. Membrane Association.- II. Action of rab Proteins After Transport Vesicle Formation.- E. Future Perspectives.- References.- 30 Endocytic Function in Cell-Free System.- A. Introduction.- B. Development of Cell-Free Assays.- I. Endosomal Fusion.- II. Early Endocytic Events: Formation, Invagination, and Budding of Coated Vesicles.- III. Late Endocytic Events: Sorting, Processing, and Recycling.- C. GTPases Implicated in Endocytic Traffic.- I. Evidence Supporting a Functional Role for GTPases.- II. Rab Proteins.- III. Heterotrimeric G-Proteins.- IV. ADP-Ribosylation Factors.- D. Future Prospectives.- References.- 31 Synaptic Vesicle Membrane Traffic and the Cycle of Rab3.- A. Membrane Traffic of Synaptic Vesicles in Neurons.- B. Rab3 Proteins: Structure, Posttranslational Modifications and Subcellular Localization.- C. The Cycle of Rab3A in Nerve Terminals.- References.- 32 Regulated Exocytosis and Interorganelle Vesicular Traffic: A Comparative Analysis.- A. Introduction.- B. GTPases in Membrane Traffic: Experimental Approaches.- C. GTPases in Constitutive Transport.- I. Vesicle Formation.- II. Vesicle Targeting and Fusion.- 1. Rab Proteins.- 2. ARF Proteins.- 3. Heterotrimeric G-Proteins.- D. GTPases in Regulated Exocytosis.- I. Granule Formation.- II. Granule Targeting and Fusion.- E. Regulation of the Secretory Pathways by Transduction Systems.- I. Regulated Exocytosis.- II. Constitutive Traffic.- F. Conclusions.- References.- 33 Regulated and Constitutive Secretion Studied In Vitro: Control by GTPases at Multiple Levels.- A. Introduction.- B. The Regulated Secretory Pathway: A General Mechanism for the Control of Cell-Cell Communication and Plasma Membrane Activities.- C. Controlling Passage Through the Regulated Secretory Pathway — Distinctions Between Constitutive and Regulated Secretion.- I. Exocytosis.- II. Formation of Granules.- III. Sorting of Contents.- D. Regulation of Traffic Through the Constitutive Pathway.- E. GTPases and Intracellular Membrane Transport.- I. SAR1.- II. Trimeric G-proteins.- III. The ADP-Ribosylation Factor Family.- IV. The rab Family.- F. Conclusions.- References.- 34 The Biology of ADP-Ribosylation Factors.- A. Introduction.- B. The ARF Family of Small GTPases.- I. Structural Definition.- II. Functional Definition.- C. ARF Functions in the Yeast, Saccharomyces cerevisiae.- I. Yeast ARF Genes and Proteins.- II. Phenotypes of arf Mutants.- III. Evidence that ARF Is Required in the Secretory Pathway.- D. Biochemical Characterization of ARF Proteins.- I. ARF Purified from Mammalian Sources is Heterogeneous.- II. ARF Cofactor Activity.- III. Guanine Nucleotide Binding.- IV. GTPase Activity.- V. The Role of Myristoylation.- VI. Binding of ARF to Lipid Bilayers.- VII. Evidence that ARF is Required at Several Steps in the Secretory and Endocytic Pathways.- E. Use of ARF Antibodies.- I. Abundance of Different ARF Proteins is Quite Variable.- II. Localization of ARF Proteins in Animal Cells.- F. ARF as a Regulator of Coat Protein Binding to Membranes.- I. Brefeldin A Causes Rapid Release of ARF from Golgi Stacks.- II. An In Vitro Assay for ARF as Regulator of Coat Protein Binding.- References.- 35 Molecular Characterization of ADP-Ribosylation Factors.- A. Introduction.- B. Activation of Cholera Toxin by ADP-Ribosylation Factors.- I. Mechanism of Activation of Cholera Toxin by ADP-Ribosylation Factors.- II. Guanine Nucleotide-Dependent Association of Cholera Toxin with ADP-Ribosylation Factors.- III. Activation of Escherichia coli Heat-Labile Enterotoxin by ADP-Ribosylation Factor.- C. Structure of ADP-Ribosylation Factors.- I. Deduced Amino Acid Sequences and Gene Structure of ADP-Ribosylation Factors.- II. Expression of ADP-Ribosylation Factors in Eukaryotic Species.- D. Hormonal and Developmental Regulation of ADP-Ribosylation Factors.- E. Physiological Roles for ADP-Ribosylation Factors.- References.- C. rho and rho-Like Proteins.- 36 rho and rho-Related Proteins.- A. Introduction.- B. Sequence and Structure.- C. Expression and Localisation.- D. Upstream Regulation of rho-Like Proteins.- I. Nucleotide Exchange.- II. GTP Hydrolysis.- E. Downstream Functions of rho-Like Proteins.- I. Mammalian rho Proteins.- II. The rac Proteins.- 1. rac and the Actin Cytoskeleton.- 2. rac and the Superoxide Production.- 3. Other rho-Related Proteins.- F. Conclusions.- References.- 37 The Mammalian Homolog of the Yeast Cell-Division-Cycle Protein, CDC42: Evidence for the Involvement of a Rho-Subtype GTPase in Cell Growth Regulation.- A. Growth Factor-Coupled Signal Transduction.- B. Reconstitution of an Epidermal Growth Factor Stimulated Phosphorylation of a 22-kDa GTPase.- C. Molecular Cloning of the Human Gp/G25K Protein: Identification of this Protein as the Human Homolog of the Yeast Cell Division Cycle Protein CDC42Sc.- D. Function of CDC42Sc in Saccharomyces cerevisiae.- E. Possible Involvement of CDC42Hs in Cell Growth Regulation.- I. cDNA Transfection Studies.- II. CDC42Hs Regulatory Proteins.- 1. CDC42Hs GTPase Activating Protein.- 2. CDC42Hs Guanine Nucleotide Dissociation Stimulator.- 3. CDC42Hs Guanine Nucleotide Dissociation Inhibitor.- References.- D. Regulation of and by Small GTPases.- 38 Role of Rap1B and Its Phosphorylation in Cellular Function: A Working Model.- A. Introduction: The Rap Family of Proteins.- B. Phosphorylation of Rap1b.- I. Structural Properties.- 1. cAMP-dependent Phosphorylation of Rap1b in Human Platelets.- 2. Phosphorylation of Raplb by a Neuronal Ca2+/ Calmodulin-dependent Protein Kinase, CaM Kinase Gr.- 3. Mutational Analysis of the Protein Kinase A-dependent Phosphorylation Site of Rap1b.- 4. Phosphorylation-dependent Activation of Rap1b: Role of Guanine Nucleotide Dissociation Stimulator.- II. Physiological Properties: The Platelet Model.- 1. Thrombin-induced Association of Rap1b with Ras-GTPase Activating Protein: Effect of Phosphorylation.- 2. Ras-GAP Associates with Phospholipase C?-1 in Human Platelets.- III. A Working Model and Open Questions.- References.- 39 GDP/GTP Exchange Proteins for Small GTP-Binding Proteins.- A. Introduction.- B. Physical Properties of GDP/GTP Exchange Protein.- C. Two Actions of GDP/GTP Exchange Protein and Requirement of the Posttranslational Processing of Small GTPases for GDP/GTP Exchange Protein Actions.- D. Substrate Specificity of GDP/GTP Exchange Protein and Functional Cooperation Between Guanine Nucleotide Dissociation Stimulator and Guanine Nucleotide Dissociation Inhibitor.- E. Activation of smg p21 by Protein Kinases A and G.- F. The Function of smg Guanine Nucleotide Dissociation Stimulator in Regulating Gene Expression and Cell Poliferation.- G. The Function of smg Guanine Nucleotide Dissociation Stimulator and rho Guanine Nucleotide Dissociation Inhibitor in Regulating Superoxide Generation.- H. The Function of smg Guanine Nucleotide Dissociation Stimulator, rho, and rho Guanine Nucleotide Dissociation Inhibitor in Regulating the Actomyosin System.- I. The Function of smg p25 Guanine Nucleotide Dissociation Inhibitor in Regulating Intracellular Vesicle Transport.- J. Conclusions.- References.- 40 GTP-Mediated Communication Between Intracellular Calcium Pools.- A. Intracellular Ca2+ Signaling Pools.- I. Nature of Intracellular Ca2+ Pools.- II. Movements of Ca2+ Induced by Inositol Phosphates.- III. Intracellular Ca2+ Channels.- IV. Significance of Ca2+ Within the InsP3-Sensitive Ca2+ Pool.- B. Ca2+ Movements Activated by Guanine Nucleotides.- I. GTP-Induced Ca2+ Fluxes.- II. Ca2+ Compartments Sensitive to GTP and InsP3.- III. Distinctions Between GTP- and InsP3-Induced Ca2+ Transport.- IV. Rationale for the Action of GTP.- C. Interorganelle Translocation of Ca2+.- I. Model for GTP-Activated Ca2+ Translocation.- II. GTP-Activated Ca2+ Transfer into the InsP3-Sensitive Ca2+ Pool.- III. Isolation of InsP3-Releasable and InsP3-Recruitable Pools.- IV. Functional Organization of Ca2+-Regulatory Organelles.- D. G-Proteins and Interorganelle Transfer of Ca2+.- I. Identification of Possible G-Protein Mediators of Ca2+ Transfer.- II. Conclusions on the Role of G-Proteins.- References.- 41 Coupling of ras to the T Cell Antigen Receptor.- A. Introduction.- B. Receptors and Intracellular Signals that Regulate p21ras.- I. Activation of p21ras in Cells Other than T Lymphocytes.- II. Activation of p21ras in T Lymphocytes.- C. GTPase Activating Proteins Regulate p21ras in T Lymphocytes.- D. Mechanisms of Regulation of ras GTPase Activating Proteins in T Cells.- E. Function of p21ras in T Lymphocytes.- References.- 42 GTPases as Regulators of Regulated Secretion.- A. GTP: A Sine Qua Non for Exocytosis.- I. Ca2+-Dependent Secretion in Myeloid Granulocytes.- B. Probing Exocytosis: Permeabilised Cells.- I. GTP?S-Induced, Ca2+-Independent Exocytosis.- II. Ca2+-Induced, GTP-Dependent Exocytosis.- III. One or Two Effectors?.- 1. Chloride Suppresses and Glutamate Enhances Guanine Nucleotide Sensitivity of Exocytosis.- IV. Kinetics of Exocytosis.- 1. Mg2+ Permits Abrupt Onset.- 2. Mg2+ Deprivation Causes Onset Delays.- V. GTPases Regulate and Modulate Exocytosis in Many Cells and Tissues.- C. On the Nature of GE.- I. The Example of GS.- II. The Example of the Monomeric GTPases.- D. Single Cell Analysis of GTP?S-Induced Exocytosis.- E. Two GTPases in Regulated Exocytosis?.- References.- 43 ADP-Ribosylation of Small GTPases by Clostridium botulinum Exoenzyme C3 and Pseudomonas aeruginosa Exoenzyme S.- A. Introduction.- B. Small GTPases.- C. Clostridium botulinum Exoenzyme C3.- D. Pseudomonas aeruginosa Exoenzyme S.- E. Conclusions.- References.