scholarly journals Function of the N-terminus of zizimin1: autoinhibition and membrane targeting

2007 ◽  
Vol 409 (2) ◽  
pp. 525-533 ◽  
Author(s):  
Nahum Meller ◽  
M. Jody Westbrook ◽  
John D. Shannon ◽  
Chittibabu Guda ◽  
Martin A. Schwartz
Keyword(s):  
Limited Proteolysis ◽  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Pleckstrin Homology Domain ◽  
Membrane Targeting ◽  
Nucleotide Exchange ◽  
Rho Proteins ◽  
Cellular Functions ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors

Rho family small GTPases are critical regulators of multiple cellular functions. Dbl-homology-domain-containing proteins are the classical GEFs (guanine nucleotide exchange factors) responsible for activation of Rho proteins. Zizimin1 is a Cdc42-specific GEF that belongs to a second family of mammalian Rho-GEFs, CZH [CDM (Ced-5/DOCK180/Myoblast city)-zizimin homology] proteins, which possess a novel type of GEF domain. CZH proteins can be divided into a subfamily related to DOCK 180 and a subfamily related to zizimin1. The two groups share two conserved regions named the CZH1 (or DHR1) domain and the CZH2 (DHR2 or DOCKER) domains, the latter exhibiting GEF activity. We now show that limited proteolysis of zizimin1 suggests the existence of structural domains that do not correspond to those identified on the basis of homologies. We demonstrate that the N-terminal half binds to the GEF domain through three distinct areas, including the CZH1, to inhibit the interaction with Cdc42. The N-terminal PH (pleckstrin homology) domain binds phosphoinositides and mediates zizimin1 membrane targeting. These results define two novel functions for the N-terminal region of zizimin1.

ARF small GTPases in the developmental function mediated by ARF regulators GNOM and VAN3

2022 ◽  
Author(s):  
Maciek Adamowski ◽  
Ivana Matijević ◽  
Jiří Friml
Keyword(s):  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Nucleotide Exchange ◽  
Loss Of Function ◽  
Gene Group ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Gtpase Activating Proteins ◽  
Developmental Patterning ◽  
Branching Angle

ARF small GTPases are molecular switches acting in intracellular trafficking. Their cycles of activity are controlled by regulators, ARF Guanine nucleotide Exchange Factors (ARF-GEFs) and ARF GTPase Activating Proteins (ARF-GAPs). The ARF-GEF GNOM (GN) and the ARF-GAP VAN3 share a prominent function in auxin-mediated developmental patterning, but the ARFs which they might control were not identified. We conducted a loss-of-function and localization-based screening of the ARF/ARF-LIKE gene family in Arabidopsis thaliana with the primary aim of identifying functional partners of GN and VAN3, while extending the limited understanding of this gene group as a whole. We identified a function of ARLA1 in branching angle control. Mutants lacking the variably localized ARLB1, ARFB1, ARFC1, ARFD1, and ARF3, even in high order combinations, do not exhibit any evident phenotypes. Loss of function arfa1 phenotypes support a major role of ARFA1 in growth and development overall, but patterning defects typical to gn loss of function are not found. ARFA1 are not localized at the plasma membrane, where GN and VAN3 carry out developmental patterning function according to current models. Taken together, putative ARF partners of GN and VAN3 in developmental patterning cannot be conclusively identified.

scholarly journals Distinct Subclasses of Small GTPases Interact with Guanine Nucleotide Exchange Factors in a Similar Manner

1998 ◽  
Vol 18 (12) ◽  
pp. 7444-7454 ◽  
Author(s):  
Gwo-Jen Day ◽  
Raymond D. Mosteller ◽  
Daniel Broek
Keyword(s):  
Alpha Helix ◽  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Structural Determinants ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Ras Superfamily

ABSTRACT The Ras-related GTPases are small, 20- to 25-kDa proteins which cycle between an inactive GDP-bound form and an active GTP-bound state. The Ras superfamily includes the Ras, Rho, Ran, Arf, and Rab/YPT1 families, each of which controls distinct cellular functions. The crystal structures of Ras, Rac, Arf, and Ran reveal a nearly superimposible structure surrounding the GTP-binding pocket, and it is generally presumed that the Rab/YPT1 family shares this core structure. The Ras, Rac, Ran, Arf, and Rab/YPT1 families are activated by interaction with family-specific guanine nucleotide exchange factors (GEFs). The structural determinants of GTPases required for interaction with family-specific GEFs have begun to emerge. We sought to determine the sites on YPT1 which interact with GEFs. We found that mutations of YPT1 at position 42, 43, or 49 (effector loop; switch I), position 69, 71, 73, or 75 (switch II), and position 107, 109, or 115 (alpha-helix 3–loop 7 [α3-L7]) are intragenic suppressors of dominant interfering YPT1 mutant N22 (YPT1-N22), suggesting these mutations prevent YPT1-N22 from binding to and sequestering an endogenous GEF. Mutations at these positions prevent interaction with the DSS4 GEF in vitro. Mutations in the switch II and α3-L7 regions do not prevent downstream signaling in yeast when combined with a GTPase-defective (activating) mutation. Together, these results show that the YPT1 GTPase interacts with GEFs in a manner reminiscent of that for Ras and Arf in that these GTPases use divergent sequences corresponding to the switch I and II regions and α3-L7 of Ras to interact with family-specific GEFs. This finding suggests that GTPases of the Ras superfamily each may share common features of GEF-mediated guanine nucleotide exchange even though the GEFs for each of the Ras subfamilies appear evolutionarily unrelated.

scholarly journals Coordination of Grp1 recruitment mechanisms by its phosphorylation

2020 ◽  
Vol 31 (25) ◽  
pp. 2816-2825
Author(s):  
Jian Li ◽  
David G. Lambright ◽  
Victor W. Hsu
Keyword(s):  
Intracellular Transport ◽  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Transport Pathways ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Membrane Compartments ◽  
Adp Ribosylation Factor

Intracellular transport pathways are initiated by the recruitment of guanine nucleotide exchange factors (GEFs) that act on the ADP-Ribosylation Factor (ARF) family of small GTPases to membrane compartments. We have elucidated the complexity of recruitment mechanisms that need to be coordinated in localizing an ARF GEF for this process.

scholarly journals The Dbs PH domain contributes independently to membrane targeting and regulation of guanine nucleotide-exchange activity

2006 ◽  
Vol 400 (3) ◽  
pp. 563-572 ◽  
Author(s):  
Mark A. Baumeister ◽  
Kent L. Rossman ◽  
John Sondek ◽  
Mark A. Lemmon
Keyword(s):  
Rho Gtpases ◽  
Regulatory Role ◽  
Pleckstrin Homology Domain ◽  
Membrane Targeting ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Ph Domain ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Dh Domain

Dbl family GEFs (guanine nucleotide-exchange factors) for the Rho GTPases almost invariably contain a PH (pleckstrin homology) domain adjacent to their DH (Dbl homology) domain. The DH domain is responsible for GEF activity, and the PH domain plays a regulatory role that remains poorly understood. We demonstrated previously that Dbl family PH domains bind phosphoinositides with low affinity and cannot function as independent membrane targeting modules. In the present study, we show that dimerization of a Dbs (Dbl's big sister) DH/PH domain fragment is sufficient to drive it to the plasma membrane through a mechanism involving PH domain–phosphoinositide interactions. Thus, the Dbs PH domain could play a significant role in membrane targeting if it co-operates with other domains in the protein. We also show that mutations that prevent phosphoinositide binding by the Dbs PH domain significantly impair cellular GEF activity even in chimaeric proteins that are robustly membrane targeted by farnesylation or by the PH domain of phospholipase C-δ1. This finding argues that the Dbs PH domain plays a regulatory role that is independent of its ability to aid membrane targeting. Thus, we suggest that the PH domain plays dual roles, contributing independently to membrane localization of Dbs (as part of a multi-domain interaction) and allosteric regulation of the DH domain.

Regulation of Rap GTPases in mammalian neurons

2016 ◽  
Vol 397 (10) ◽  
pp. 1055-1069 ◽  
Author(s):  
Bhavin Shah ◽  
Andreas W. Püschel
Keyword(s):  
Nervous System ◽  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Nucleotide Exchange ◽  
Cellular Processes ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Gtpase Activating Proteins ◽  
Mature Neurons

Abstract Small GTPases are central regulators of many cellular processes. The highly conserved Rap GTPases perform essential functions in the mammalian nervous system during development and in mature neurons. During neocortical development, Rap1 is required to regulate cadherin- and integrin-mediated adhesion. In the adult nervous system Rap1 and Rap2 regulate the maturation and plasticity of dendritic spine and synapses. Although genetic studies have revealed important roles of Rap GTPases in neurons, their regulation by guanine nucleotide exchange factors (GEFs) that activate them and GTPase activating proteins (GAPs) that inactivate them by stimulating their intrinsic GTPase activity is just beginning to be explored in vivo. Here we review how GEFs and GAPs regulate Rap GTPases in the nervous system with a focus on their in vivo function.

Regulation of Ras in lymphocytes: get a GRP

2006 ◽  
Vol 34 (5) ◽  
pp. 858-861 ◽  
Author(s):  
J.C. Stone
Keyword(s):  
Cell Receptor ◽  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
C1 Domain ◽  
Ef Hands ◽  
Ras Signalling

RasGRPs (guanine nucleotide releasing proteins) are a family of four GEFs (guanine nucleotide-exchange factors) (Ras GEFs) that positively regulate Ras and related small GTPases. RasGRP1 possesses a catalytic region consisting of a REM (Ras exchange motif) and a CDC25 (cell division cycle 25) domain. RasGRP1 also possesses a DAG (diacylglycerol)-binding C1 domain and a pair of EF hands that bind calcium. RasGRP1 is selectively expressed in lymphocytes as well as in some cells of the brain, kidney and skin. Functional analysis supports the hypothesis that RasGRP1 serves to couple TCR (T-cell receptor) stimulation and phospholipase C activation with Ras signalling. In B-cells, both RasGRP1 and RasGRP3 play a similar role downstream of the B-cell receptor. RasGRP2 acts on the Ras-related protein Rap and functions in platelet adhesion. RasGRP4 is expressed in mast cells and certain myeloid leukaemia cells. Membrane DAG regulates RasGRPs directly by recruitment to cellular membranes, as well as indirectly by protein kinase C-mediated phosphorylation. The properties of RasGRPs provide a novel view of Ras regulation in lymphocytes and explain several earlier observations. Many experimental results obtained with DAG analogues could be reviewed in light of these findings.

Role of Epac in brain and heart

2012 ◽  
Vol 40 (1) ◽  
pp. 51-57 ◽  
Author(s):  
Anne-Coline Laurent ◽  
Magali Breckler ◽  
Magali Berthouze ◽  
Frank Lezoualc'h
Keyword(s):  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Signalling Pathways ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
New Sensors ◽  
Kinase A

Epacs (exchange proteins directly activated by cAMP) are guanine-nucleotide-exchange factors for the Ras-like small GTPases Rap1 and Rap2. Epacs were discovered in 1998 as new sensors for the second messenger cAMP acting in parallel to PKA (protein kinase A). As cAMP regulates many important physiological functions in brain and heart, the existence of Epacs raises many questions regarding their role in these tissues. The present review focuses on the biological roles and signalling pathways of Epacs in neurons and cardiac myocytes. We discuss the potential involvement of Epacs in the manifestation of cardiac and central diseases such as cardiac hypertrophy and memory disorders.

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