RhoGDI-3 regulates RhoG and targets this protein to the Golgi complex through its unique N-terminal domain.
Guanine nucleotide dissociation inhibitors (GDIs) regulate both GDP/GTP and membrane association/dissociation cycles of Rho/Rac and Rab proteins.RhoGDI-3 is distinguishable from other rhoGDI proteins by its partial association with a detergent-resistant subcellular fraction. Here, we investigate the activity of this unusual rhoGDI using confocal laser scanning microscopy, immuno-isolation, and rhoGDI-3 mutants. We establish that the noncytosolic fraction of rhoGDI-3 is associated with the Golgi apparatus. The domain involved in this association is the unique N-terminal segment of rhoGDI-3 predicted to form an amphipathic alpha helix. This peptide is indispensable for Golgi association of rhoGDI-3 and sufficient to address a green fluorescent protein to the Golgi apparatus. Site-directed mutations, decreasing the hydrophobic surface of the helix, localize rhoGDI-3 into the cytoplasm. We establish that rhoGDI-3 is able to inhibit activation of the RhoG protein and to target this protein to the Golgi apparatus. Furthermore, we demonstrate the importance of the rhoGDI-3 N-terminal segment for both Golgi targeting and stability of the cytoplasmic RhoG/rhoGDI-3 complex. RhoGDI-3 is the first example of a GDI directly involved in the delivery of a Rho protein to a specific subcellular compartment.
Brunet
Nicolas
N
Laboratoire d'Enzymologie et Biochimie Structurales, CNRS UPR 9063, F-91198 Gif-sur-Yvette, France.
Morin
Annie
A
Olofsson
Birgitta
B
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000737:chemistry / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid; D020741:rho GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
C569638:ARHGDIA protein, human; D020730:Guanine Nucleotide Dissociation Inhibitors; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D020741:rho GTP-Binding Proteins