title: Dissociation of GDP dissociation inhibitor and membrane translocation are required for efficient activation of Rac by the Dbl homology-pleckstrin homology region of Tiam.
abstract: Small G proteins of the Rho/Rac/Cdc42 family are associated with lipid membranes through their prenylated C termini. Alternatively, these proteins form soluble complexes with GDI proteins. To assess how this membrane partitioning influences the activation of Rac by guanine nucleotide exchange factors, GDP-to-GTP exchange reactions were performed in the presence of liposomes using different forms of Rac-GDP. We show that both non-prenylated Rac-GDP and the soluble complex between prenylated Rac-GDP and GDI are poorly activated by the Dbl homology-pleckstrin homology (DH-PH) domain of the exchange factor Tiam1, whereas prenylated Rac-GDP bound to liposomes is activated about 10 times more rapidly. Sedimentation experiments with liposomes reveal that the DH-PH region of Tiam1 forms, with nucleotide-free prenylated Rac, a membrane-bound complex from which GDI is excluded. Taken together, these experiments demonstrate that the dissociation of Rac-GDP from GDI and its translocation to membrane lipids favor DH-PH-catalyzed nucleotide exchange because the steric hindrance caused by GDI is relieved and because the membrane environment favors functional interaction between the DH-PH domain and the small G protein.
authors.affiliation: CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, 660 Route des Lucioles, 06560 Valbonne, France.
authors.forename: Karine
authors.initials: K
authors.lastname: Robbe
authors.forename: Annie
authors.initials: A
authors.lastname: Otto-Bruc
authors.forename: Pierre
authors.initials: P
authors.lastname: Chardin
authors.forename: Bruno
authors.initials: B
authors.lastname: Antonny
mesh_terms: D001798:Blood Proteins / Q000235:genetics; D005786:Gene Expression Regulation; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000235:genetics / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D008081:Liposomes; D010750:Phosphoproteins / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D011506:Proteins / Q000235:genetics*; D011518:Proto-Oncogene Proteins; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics; D012441:Saccharomyces cerevisiae; D017385:Sequence Homology; D015398:Signal Transduction / Q000235:genetics; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D014162:Transfection; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
chemical_list: D001798:Blood Proteins; D020730:Guanine Nucleotide Dissociation Inhibitors; D020662:Guanine Nucleotide Exchange Factors; D008081:Liposomes; C057811:MCF2 protein, human; D010750:Phosphoproteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D015682:Retroviridae Proteins, Oncogenic; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; C039077:platelet protein P47; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins