scholarly journals Ccpg1, a Novel Scaffold Protein That Regulates the Activity of the Rho Guanine Nucleotide Exchange Factor Dbs

2006 ◽  
Vol 26 (23) ◽  
pp. 8964-8975 ◽  
Author(s):  
Elena V. Kostenko ◽  
Oyenike O. Olabisi ◽  
Sutapa Sahay ◽  
Pedro L. Rodriguez ◽  
Ian P. Whitehead
Keyword(s):  
Family Member ◽  
Guanine Nucleotide Exchange Factor ◽  
Scaffold Protein ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Novel Scaffold ◽  
Exchange Activity

ABSTRACT Dbs is a Rho-specific guanine nucleotide exchange factor (RhoGEF) with in vitro exchange activity specific for RhoA and Cdc42. Like many RhoGEF family members, the in vivo exchange activity of Dbs is restricted in a cell-specific manner. Here we report the characterization of a novel scaffold protein (designated cell cycle progression protein 1 [Ccpg1]) that interacts with Dbs and modulates its in vivo exchange specificity. When coexpressed in mammalian cells, Ccpg1 binds to the Dbl homology/pleckstrin homology domain tandem motif of Dbs and inhibits its exchange activity toward RhoA, but not Cdc42. Expression of Ccpg1 correlates with the ability of Dbs to activate endogenous RhoA in cultured cells, and suppression of endogenous Ccpg1 expression potentiates Dbs exchange activity toward RhoA. The isolated Dbs binding domain of Ccpg1 is not sufficient to suppress Dbs exchange activity on RhoA, thus suggesting a regulatory interaction. Ccpg1 mediates recruitment of endogenous Src kinase into Dbs-containing complexes and interacts with the Rho family member Cdc42. Collectively, our studies suggest that Ccpg1 represents a new class of regulatory scaffold protein that can function as both an assembly platform for Rho protein signaling complexes and a regulatory protein which can restrict the substrate utilization of a promiscuous RhoGEF family member.

scholarly journals The Rho-Guanine Nucleotide Exchange Factor Domain of Obscurin Activates RhoA Signaling in Skeletal Muscle

2009 ◽  
Vol 20 (17) ◽  
pp. 3905-3917 ◽  
Author(s):  
Diana L. Ford-Speelman ◽  
Joseph A. Roche ◽  
Amber L. Bowman ◽  
Robert J. Bloch
Keyword(s):  
Skeletal Muscle ◽  
Guanine Nucleotide Exchange Factor ◽  
Small Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

Obscurin is a large (∼800-kDa), modular protein of striated muscle that concentrates around the M-bands and Z-disks of each sarcomere, where it is well positioned to sense contractile activity. Obscurin contains several signaling domains, including a rho-guanine nucleotide exchange factor (rhoGEF) domain and tandem pleckstrin homology domain, consistent with a role in rho signaling in muscle. We investigated the ability of obscurin's rhoGEF domain to interact with and activate small GTPases. Using a combination of in vitro and in vivo approaches, we found that the rhoGEF domain of obscurin binds selectively to rhoA, and that rhoA colocalizes with obscurin at the M-band in skeletal muscle. Other small GTPases, including rac1 and cdc42, neither associate with the rhoGEF domain of obscurin nor concentrate at the level of the M-bands. Furthermore, overexpression of the rhoGEF domain of obscurin in adult skeletal muscle selectively increases rhoA expression and activity in this tissue. Overexpression of obscurin's rhoGEF domain and its effects on rhoA alter the expression of rho kinase and citron kinase, both of which can be activated by rhoA in other tissues. Injuries to rodent hindlimb muscles caused by large-strain lengthening contractions increases rhoA activity and displaces it from the M-bands to Z-disks, similar to the effects of overexpression of obscurin's rhoGEF domain. Our results suggest that obscurin's rhoGEF domain signals at least in part by inducing rhoA expression and activation, and altering the expression of downstream kinases in vitro and in vivo.

scholarly journals Crystal and cryo-EM structures of the cytosolic G protein alpha chaperone and guanine nucleotide exchange factor Ric-8A bound to Gαi1

2020 ◽  
Author(s):  
Levi J. McClelland ◽  
Kaiming Zhang ◽  
Tung-Chung Mou ◽  
Jake Johnston ◽  
Cindee Yates-Hansen ◽  
...  
Keyword(s):  
G Protein ◽  
Domain Architecture ◽  
Guanine Nucleotide Exchange Factor ◽  
Chaperone Activity ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor

Ric-8A is a cytosolic Guanine Nucleotide exchange Factor (GEF) that activates heterotrimeric G protein alpha subunits (Gα)1. Ric-8A is essential to life in multicellular eukaryotes by virtue of its chaperone activity that is required for Gα biogenesis and membrane localization2, 3. Ric-8A adopts an armadillo (ARM)/HEAT repeat domain architecture and is structurally unrelated to G Protein-Coupled Receptors (GPCR)4. Both GEF and chaperone activities are stimulated by Casein Kinase II phosphorylation5. The mechanisms by which Ric-8A catalyzes GDP release and GTP binding to Gα, or exerts chaperone activity are unknown. Here, we report the structure of the nanobody-stabilized complex of nucleotide-free Gαi1 (isoform 1 of Gα family i) and phosphorylated Ric-8A at near atomic resolution by cryo-electron microscopy and X-ray crystallography. We find that Ric-8A envelops the GTPase domain of Gα, disrupting all three switch regions that convey Gα nucleotide-binding and signaling activity, and displaces the C-terminal helix and helical domain of Gα. These cooperative interactions dismantle the GDP binding site and promote GDP release, while protecting structural elements of Gα that are dynamic in the nucleotide-free state. The structures also show how in vivo phosphorylation stabilizes Gα-binding elements of Ric-8A, thereby enhancing its GEF and chaperone activities.

scholarly journals Ypt32 recruits the Sec4p guanine nucleotide exchange factor, Sec2p, to secretory vesicles; evidence for a Rab cascade in yeast

2002 ◽  
Vol 157 (6) ◽  
pp. 1005-1016 ◽  
Author(s):  
Darinel Ortiz ◽  
Martina Medkova ◽  
Christiane Walch-Solimena ◽  
Peter Novick
Keyword(s):  
Plasma Membrane ◽  
Guanine Nucleotide Exchange Factor ◽  
Secretory Vesicles ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Polarized Transport ◽  
Exchange Activity

SEC2 is an essential gene required for polarized growth of the yeast Saccharomyces cerevisiae. It encodes a protein of 759 amino acids that functions as a guanine nucleotide exchange factor for the small GTPase Sec4p, a regulator of Golgi to plasma membrane transport. Activation of Sec4p by Sec2p is needed for polarized transport of vesicles to exocytic sites. Temperature-sensitive (ts) mutations in sec2 and sec4 result in a tight block in secretion and the accumulation of secretory vesicles randomly distributed in the cell. The proper localization of Sec2p to secretory vesicles is essential for its function and is largely independent of Sec4p. Although the ts mutation sec2-78 does not affect nucleotide exchange activity, the protein is mislocalized. Here we present evidence that Ypt31/32p, members of Rab family of GTPases, regulate Sec2p function. First, YPT31/YPT32 suppress the sec2-78 mutation. Second, overexpression of Ypt31/32p restores localization of Sec2-78p. Third, Ypt32p and Sec2p interact biochemically, but Sec2p has no exchange activity on Ypt32p. We propose that Ypt32p and Sec4p act as part of a signaling cascade in which Ypt32p recruits Sec2p to secretory vesicles; once on the vesicle, Sec2p activates Sec4p, enabling the polarized transport of vesicles to the plasma membrane.

scholarly journals The two guanine nucleotide exchange factor domains of Trio link the Rac1 and the RhoA pathways in vivo

Oncogene ◽  
1998 ◽  
Vol 16 (2) ◽  
pp. 147-152 ◽  
Author(s):  
Jean-Michel Bellanger ◽  
Jean-Bernard Lazaro ◽  
Sylvie Diriong ◽  
Anne Fernandez ◽  
Ned Lamb ◽  
...  
Keyword(s):  
Guanine Nucleotide Exchange Factor ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Exchange Factor ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor
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