Misplaced Pages

#758241

24-620: Guanine nucleotide exchange factors (GEFs) are proteins or protein domains involved in the activation of small GTPases . Small GTPases act as molecular switches in intracellular signaling pathways and have many downstream targets. The most well-known GTPases comprise the Ras superfamily and are involved in essential cell processes such as cell differentiation and proliferation, cytoskeletal organization, vesicle trafficking, and nuclear transport. GTPases are active when bound to GTP and inactive when bound to GDP, allowing their activity to be regulated by GEFs and

48-506: A guanine nucleotide exchange factor (GEF) domain for small G proteins of the Rho family . DHR2 domains bear no significant similarity to the well described DH domain ( D bl h omologous domain) present in other RhoGEFs such as Vav , P-Rex and TRIO . Indeed, the most divergent mammalian DHR2 domains share only 16-17% sequence similarity . References [ edit ] ^ Meller N, Merlot S, Guda C (November 2005). "CZH proteins:

72-585: A Dbl Homology domain ( DH domain ), responsible for GEF catalytic activity for Rho GTPases . The human genome encodes 71 members, distributed into 20 subfamilies. All 71 members were already present in early Vertebrates, and most of the 20 subfamilies were already present in early Metazoans. Many of the mammalian Dbl family proteins are tissue-specific and their number in Metazoa varies in proportion of cell signaling complexity. Pleckstrin homology domains ( PH domains ) are associated in tandem with DH domains in 64 of

96-407: A conserved Sec 7 domain. This 200 amino acid region is homologous to the yeast Sec7p protein. GEFs are often recruited by adaptor proteins in response to upstream signals. GEFs are multi-domain proteins and interact with other proteins inside the cell through these domains. Adaptor proteins can modulate GEF activity by interacting with other domains besides the catalytic domain. For example, SOS 1,

120-1182: A new family of Rho-GEFs" . J. Cell Sci . 118 (Pt 21): 4937–46. doi : 10.1242/jcs.02671 . PMID   16254241 . ^ Côté JF, Vuori K (December 2002). "Identification of an evolutionarily conserved superfamily of DOCK180-related proteins with guanine nucleotide exchange activity" . J. Cell Sci . 115 (Pt 24): 4901–13. doi : 10.1242/jcs.00219 . PMID   12432077 . Further reading [ edit ] Côté JF, Vuori K (2007). "GEF what? Dock180 and related proteins help Rac to polarize cells in new ways" . Trends Cell Biol . 17 (8): 383–393. doi : 10.1016/j.tcb.2007.05.001 . PMC   2887429 . PMID   17765544 . Côté JF, Vuori K (2006). "In Vitro Guanine Nucleotide Exchange Activity of DHR-2/DOCKER/CZH2 Domains". Regulators and Effectors of Small GTPases: Rho Family . Methods in Enzymology. Vol. 406. pp. 41–57. doi : 10.1016/S0076-6879(06)06004-6 . ISBN   9780121828110 . PMID   16472648 . Lu M, Kinchen JM, Rossman KL, et al. (2005). "GEF A Steric-inhibition model for regulation of nucleotide exchange via

144-666: A role in GEF activation. Crosstalk has also been shown between GEFs and multiple GTPase signaling pathways. For example, SOS contains a Dbl homology domain in addition to its CDC25 catalytic domain. SOS can act as a GEF to activate Rac1 , a RhoGTPase, in addition to its role as a GEF for Ras. SOS is therefore a link between the Ras-Family and Rho-Family GTPase signaling pathways. GEFs are potential target for cancer therapy due to their role in many signaling pathways, particularly cell proliferation. For example, many cancers are caused by mutations in

168-408: A role in regulating these pathways through their activation of GTPases. Small GTPases Small GTPases ( EC 3.6.5.2 ), also known as small G-proteins , are a family of hydrolase enzymes that can bind and hydrolyze guanosine triphosphate (GTP). They are a type of G-protein found in the cytosol that are homologous to the alpha subunit of heterotrimeric G-proteins , but unlike

192-681: Is also present in other proteins beyond RhoGEFs. The DHR2 domain is the catalytic domain of the DOCK family of Rho GEFs. Like DH domain , DHR2 was already present at the origin of eukaryotes. The DOCK family is a separate subset of GEFs from the Dbl family and bears no structural or sequence relation to the DH domain. There are 11 identified DOCK family members divided into subfamilies based on their activation of Rac and Cdc42 . DOCK family members are involved in cell migration, morphogenesis and phagocytosis. The DHR2 domain

216-475: Is approximately 400 amino acids. These proteins also contain a second conserved domain, DHR1, which is approximately 250 amino acids. The DHR1 domain been shown to be involved in the membrane localization of some GEFs. The Sec7 domain is responsible for the GEF catalytic activity in ARF GTPases . ARF proteins function in vesicle trafficking. Though ARF GEFs are divergent in their overall sequences, they contain

240-699: Is common among GEFs, the specific interactions between the regions of the GTPase and GEF vary among individual proteins. Some GEFs are specific to a single GTPase while others have multiple GTPase substrates. While different subfamilies of Ras superfamily GTPases have a conserved GTP binding domain, this is not the case for GEFs. Different families of GEFs correspond to different Ras subfamilies. The functional domains of these GEF families are not structurally related and do not share sequence homology. These GEF domains appear to be evolutionarily unrelated despite similar function and substrates. The CDC25 homology domain, also called

264-554: Is further divided into 6 subfamilies: Ras , Ral , Rit , Rap , Rheb , and Rad . Miro is a recent contributor to the superfamily. Each subfamily shares the common core G domain, which provides essential GTPase and nucleotide exchange activity. The surrounding sequence helps determine the functional specificity of the small GTPase, for example the 'Insert Loop', common to the Rho subfamily, specifically contributes to binding to effector proteins such as IQGAP and WASP . The Ras family

SECTION 10

#1732863363759

288-574: Is generally responsible for cell proliferation, Rho for cell morphology, Ran for nuclear transport and Rab and Arf for vesicle transport. DHR2 domain From Misplaced Pages, the 💕 Protein domain DHR2 ( D OCK h omology r egion 2), also known as CZH2 or Docker2 , is a protein domain of approximately 450-550 amino acids that is present in the DOCK family of proteins. This domain functions as

312-484: Is hydrolyzed to GDP). The GDP can then be replaced by free GTP. Therefore, a G-protein can be switched on and off. GTP hydrolysis is accelerated by GTPase activating proteins (GAPs), while GTP exchange is catalyzed by guanine nucleotide exchange factors (GEFs). Activation of a GEF typically activates its cognate G-protein, while activation of a GAP results in inactivation of the cognate G-protein. Guanosine nucleotide dissociation inhibitors (GDI) maintain small GTPases in

336-473: The MAPK/ERK pathway that lead to uncontrolled growth. The GEF SOS1 activates Ras, whose target is the kinase Raf . Raf is a proto-oncogene because mutations in this protein have been found in many cancers. The Rho GTPase Vav1 , which can be activated by the GEF receptor, has been shown to promote tumor proliferation in pancreatic cancer. GEFs represent possible therapeutic targets as they can potentially play

360-509: The RasGEF domain , is the catalytic domain of many Ras GEFs, which activate Ras GTPases. The CDC25 domain comprises approximately 500 amino acids and was first identified in the CDC25 protein in budding yeast ( Saccharomyces cerevisiae ) . Dbl-like RhoGEFs were present at the origin of eukaryotes and evolved as highly adaptive cell signaling mediators. Dbl-like RhoGEFs are characterized by the presence of

384-474: The 71 Dbl family members. The PH domain is located immediately adjacent to the C terminus of the DH domain. Together, these two domains constitute the minimum structural unit necessary for the activity of most Dbl family proteins. The PH domain is involved in intracellular targeting of the DH domain. It is generally thought to modulate membrane binding through interactions with phospholipids, but its function has been shown to vary in different proteins. This PH domain

408-486: The GTPase results in the release of the GEF, which can then activate a new GTPase. Thus, GEFs both destabilize the GTPase interaction with GDP and stabilize the nucleotide-free GTPase until a GTP molecule binds to it. GAPs (GTPase-activating protein) act antagonistically to inactivate GTPases by increasing their intrinsic rate of GTP hydrolysis. GDP remains bound to the inactive GTPase until a GEF binds and stimulates its release. The localization of GEFs can determine where in

432-432: The P loop and switch regions of the GTPase while the rest of the structure is largely unchanged. The binding of the GEF sterically hinders the magnesium-binding site and interferes with the phosphate-binding region, while the base-binding region remains accessible. When the GEF binds the GTPase, the phosphate groups are released first and the GEF is displaced upon binding of the entering GTP molecule. Though this general scheme

456-561: The Ras GEF in the MAPK/ERK pathway , is recruited by the adaptor protein GRB2 in response to EGF receptor activation. The binding of SOS1 to GRB2 localizes it to the plasma membrane, where it can activate the membrane-bound Ras . Other GEFs, such as the Rho GEF Vav1 , are activated upon phosphorylation in response to upstream signals. Secondary messengers such as cAMP and calcium can also play

480-498: The alpha subunit of G proteins, a small GTPase can function independently as a hydrolase enzyme to bind to and hydrolyze a guanosine triphosphate (GTP) to form guanosine diphosphate (GDP). The best-known members are the Ras GTPases and hence they are sometimes called Ras subfamily GTPases . A typical G-protein is active when bound to GTP and inactive when bound to GDP (i.e. when the GTP

504-626: The cell a particular GTPase will be active. For example, the Ran GEF, RCC1 , is present in the nucleus while the Ran GAP is present in the cytosol, modulating nuclear import and export of proteins. RCC1 converts RanGDP to RanGTP in the nucleus, activating Ran for the export of proteins. When the Ran GAP catalyzes conversion of RanGTP to RanGDP in the cytosol, the protein cargo is released. The mechanism of GTPase activation varies among different GEFs. However, there are some similarities in how different GEFs alter

SECTION 20

#1732863363759

528-413: The conformation of the G protein nucleotide-binding site. GTPases contain two loops called switch 1 and switch 2 that are situated on either side of the bound nucleotide. These regions and the phosphate -binding loop of the GTPase interact with the phosphates of the nucleotide and a coordinating magnesium ion to maintain high affinity binding of the nucleotide. GEF binding induces conformational changes in

552-460: The inactive state. Small GTPases regulate a wide variety of processes in the cell , including growth, cellular differentiation , cell movement and lipid vesicle transport. There are more than a hundred proteins in the Ras superfamily. Based on structure, sequence and function, the Ras superfamily is divided into five main families, (Ras, Rho , Ran , Rab and Arf GTPases). The Ras family itself

576-444: The opposing GTPase activating proteins (GAPs). GDP dissociates from inactive GTPases very slowly. The binding of GEFs to their GTPase substrates catalyzes the dissociation of GDP, allowing a GTP molecule to bind in its place. GEFs function to promote the dissociation of GDP. After GDP has disassociated from the GTPase, GTP generally binds in its place, as the cytosolic ratio of GTP is much higher than GDP at 10:1. The binding of GTP to

#758241