scholarly journals Rab GTPase localization and Rab cascades in Golgi transport

2012 ◽  
Vol 40 (6) ◽  
pp. 1373-1377 ◽  
Author(s):  
Suzanne R. Pfeffer
Keyword(s):  
Effector Proteins ◽  
Membrane Microdomains ◽  
Rab Gtpase ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Golgi Transport ◽  
Guanine Nucleotide Dissociation Inhibitor ◽  
Membrane Bound ◽  
Effector Binding ◽  
Endocytic Pathways

Rab GTPases are master regulators of membrane traffic. By binding to distinct sets of effector proteins, Rabs catalyse the formation of function-specifying membrane microdomains. They are delivered to membranes by a protein named GDI (guanine-nucleotide-dissociation inhibitor) and are stabilized there after nucleotide exchange by effector binding. In the present mini-review, I discuss what we know about how Rab GTPases are delivered to the correct membrane-bound compartments and how Rab GTPase cascades order Rabs within the secretory and endocytic pathways. Finally, I describe how Rab cascades may establish the distinct compartments of the Golgi complex to permit ordered processing, sorting and secretion of secretory cargoes.

scholarly journals Rab GTPases: master regulators that establish the secretory and endocytic pathways

2017 ◽  
Vol 28 (6) ◽  
pp. 712-715 ◽  
Author(s):  
Suzanne R. Pfeffer
Keyword(s):  
Membrane Trafficking ◽  
Membrane Microdomains ◽  
Rab Gtpase ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Open Questions ◽  
Endocytic Pathways

Several of the most important discoveries in the field of membrane traffic have come from studies of Rab GTPases by Marino Zerial and Peter Novick and their colleagues. Zerial was the first to discover that Rab GTPases represent identity markers for different membrane-bound compartments, and each Rab organizes a collection of specific effectors into function-specifying membrane microdomains to carry out receptor trafficking. Novick discovered that the order (and thus polarity) of Rab GTPases along the secretory and endocytic pathways are established by their specific, cognate guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), which partner with one Rab to regulate the subsequent- and prior-acting Rabs. Such so-called Rab cascades have evolved to establish domains that contain unique Rab proteins and their cognate effectors, which drive all steps of membrane trafficking. These findings deserve much broader recognition by the biomedical research community and are highlighted here, along with open questions that require serious attention for full understanding of the molecular basis of Rab GTPase-regulated membrane trafficking in eukaryotic cells.

scholarly journals The Hsp90 Chaperone Complex Regulates GDI-dependent Rab Recycling

2006 ◽  
Vol 17 (8) ◽  
pp. 3494-3507 ◽  
Author(s):  
Christine Y. Chen ◽  
William E. Balch
Keyword(s):  
Rab Gtpase ◽  
Rab Gtpases ◽  
Coding System ◽  
Golgi Transport ◽  
Guanine Nucleotide Dissociation Inhibitor ◽  
Hsp90 Activity ◽  
Hsp90 Chaperone ◽  
Chaperone Complex ◽  
Hsp 90 ◽  
Synaptic Vesicle Fusion

Rab GTPase regulated hubs provide a framework for an integrated coding system, the membrome network, that controls the dynamics of the specialized exocytic and endocytic membrane architectures found in eukaryotic cells. Herein, we report that Rab recycling in the early exocytic pathways involves the heat-shock protein (Hsp)90 chaperone system. We find that Hsp90 forms a complex with guanine nucleotide dissociation inhibitor (GDI) to direct recycling of the client substrate Rab1 required for endoplasmic reticulum (ER)-to-Golgi transport. ER-to-Golgi traffic is inhibited by the Hsp90-specific inhibitors geldanamycin (GA), 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG), and radicicol. Hsp90 activity is required to form a functional GDI complex to retrieve Rab1 from the membrane. Moreover, we find that Hsp90 is essential for Rab1-dependent Golgi assembly. The observation that the highly divergent Rab GTPases Rab1 involved in ER-to-Golgi transport and Rab3A involved in synaptic vesicle fusion require Hsp90 for retrieval from membranes lead us to now propose that the Hsp90 chaperone system may function as a general regulator for Rab GTPase recycling in exocytic and endocytic trafficking pathways involved in cell signaling and proliferation.

A model for Rab GTPase localization

2005 ◽  
Vol 33 (4) ◽  
pp. 627-630 ◽  
Author(s):  
S. Pfeffer
Keyword(s):  
Steady State ◽  
Cellular Localization ◽  
Rab Gtpase ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Macromolecular Assemblies ◽  
Complex Interactions ◽  
Membrane Compartment ◽  
Membrane Bound ◽  
Distinct Membrane

The human genome encodes almost 70 Rab GTPases. These proteins are C-terminally geranylgeranylated and are localized to the surfaces of distinct membrane-bound compartments in eukaryotic cells. This mini review presents a working model for how Rabs achieve and maintain their steady-state localizations. Data from a number of laboratories suggest that Rabs participate in the generation of macromolecular assemblies that generate functional microdomains within a given membrane compartment. Our data suggest that these complex interactions are important for the cellular localization of Rab proteins at steady state.

scholarly journals Stochastic activation and bistability in a Rab GTPase regulatory network

2019 ◽  
Author(s):  
Urban Bezeljak ◽  
Hrushikesh Loya ◽  
Beata Kaczmarek ◽  
Timothy E. Saunders ◽  
Martin Loose
Keyword(s):  
Positive Feedback ◽  
Regulatory Network ◽  
Signaling Networks ◽  
Rab Gtpase ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Intracellular Traffic ◽  
Bistable Switching ◽  
In Vitro Reconstitution

AbstractRab GTPases are the central regulators of intracellular traffic. Their function relies on a conformational change triggered by nucleotide exchange and hydrolysis. While this switch is well understood for an individual protein, how Rab GTPases collectively transition between states to generate a biochemical signal in space and time is unclear. Here, we combine in vitro reconstitution experiments with theoretical modeling to study a minimal Rab5 activation network. We find that positive feedback in this network gives rise to bistable switching of Rab5 activation and provide evidence that controlling the inactive population of Rab5 on the membrane can shape the network response. Together, our findings reveal new insights into the non-equilibrium properties and general principles of biochemical signaling networks underlying the spatiotemporal organization of the cell.

scholarly journals AMPylation Is Critical for Rab1 Localization to Vacuoles Containing Legionella pneumophila

mBio ◽  
2014 ◽  
Vol 5 (1) ◽  
Author(s):  
Camille A. Hardiman ◽  
Craig R. Roy
Keyword(s):  
Legionella Pneumophila ◽  
Effector Proteins ◽  
Host Protein ◽  
Effector Protein ◽  
Intracellular Pathogen ◽  
Effective Strategy ◽  
Nucleotide Exchange ◽  
Content Type ◽  
Cell Functions ◽  
Membrane Bound

ABSTRACTLegionella pneumophilais an intracellular pathogen that resides within a membrane-bound compartment that is derived from vesicles exiting the endoplasmic reticulum (ER). To create this compartment, these bacteria use a type IV secretion system to deliver effector proteins that subvert host cell functions. SeveralLegionellaeffector proteins modulate the function of the host protein Rab1, which is a GTPase that is recruited to theLegionella-containing vacuole (LCV). Here, we examined which of the Rab1-directed enzymatic activities displayed byLegionellaeffectors are important for localizing the Rab1 protein to the LCV membrane. The guanine nucleotide exchange factor (GEF) domain in the effector protein DrrA (SidM) was essential for Rab1 recruitment to the LCV and Rab1 AMPylation by the nucleotidyltransferase domain in DrrA was important for Rab1 retention.Legionellaorganisms producing mutant DrrA proteins that were severely attenuated for GEF activityin vitroretained the ability to localize Rab1 to the LCV. Rab1 localization to the LCV mediated by these GEF-defective mutants required AMPylation. Importantly, we found that efficient localization of Rab1 to the LCV occurred when Rab1 GEF activity and Rab1 AMPylation activity were provided by separate proteins. Rab1 phosphocholination (PCylation) by the effector protein AnkX, however, was unable to substitute for Rab1 AMPylation. Lastly, the defect in Rab1 localization to the LCV in AMPylation-deficient strains ofLegionellawas partially suppressed if the GTPase-activating protein (GAP) LepB was eliminated. Thus, our data indicate that AMPylation of Rab1 is an effective strategy to maintain this GTPase on the LCV membrane.IMPORTANCEActivities that enable the intracellular pathogenLegionella pneumophilato subvert the function of the host protein Rab1 were investigated. Our data show that a posttranslational modification called AMPylation is critical for maintaining a pool of Rab1 on the LCV membrane. AMPylation of Rab1 led to the accumulation of GTP-bound Rab1 on the LCV membrane by protecting the protein from inactivation by GAPs. Importantly, PCylation of Rab1 by theLegionellaeffector protein AnkX was neither necessary nor sufficient to maintain Rab1 on the LCV, indicating that AMPylation and PCylation represent functionally distinct activities. We conclude that modification of Rab1 by AMPylation is an effective strategy to spatially and temporally regulate the function of this GTPase on a membrane-bound organelle.

scholarly journals TIP47 is a key effector for Rab9 localization

2006 ◽  
Vol 173 (6) ◽  
pp. 917-926 ◽  
Author(s):  
Dikran Aivazian ◽  
Ramon L. Serrano ◽  
Suzanne Pfeffer
Keyword(s):  
Steady State ◽  
Human Genome ◽  
Effector Proteins ◽  
Rab Gtpases ◽  
Interacting Protein ◽  
Cellular Concentration ◽  
Membrane Compartments ◽  
Effector Binding ◽  
Distinct Membrane

The human genome encodes ∼70 Rab GTPases that localize to the surfaces of distinct membrane compartments. To investigate the mechanism of Rab localization, chimeras containing heterologous Rab hypervariable domains were generated, and their ability to bind seven Rab effectors was quantified. Two chimeras could bind effectors for two distinctly localized Rabs; a Rab5/9 hybrid bound both Rab5 and Rab9 effectors, and a Rab1/9 hybrid bound to certain Rab1 and Rab9 effectors. These unusual chimeras permitted a test of the importance of effector binding for Rab localization. In both cases, changing the cellular concentration of a key Rab9 effector, which is called tail-interacting protein of 47 kD, moved a fraction of the proteins from their parental Rab localization to that of Rab9. Thus, relative concentrations of certain competing effectors could determine a chimera's localization. These data confirm the importance of effector interactions for Rab9 localization, and support a model in which effector proteins rely on Rabs as much as Rabs rely on effectors to achieve their correct steady state localizations.

scholarly journals Regulation of ER-phagy by a Ypt/Rab GTPase module

2013 ◽  
Vol 24 (19) ◽  
pp. 3133-3144 ◽  
Author(s):  
Zhanna Lipatova ◽  
Ankur H. Shah ◽  
Jane J. Kim ◽  
Jonathan W. Mulholland ◽  
Nava Segev
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Trafficking ◽  
Eukaryotic Cells ◽  
Rab Gtpase ◽  
Rab Gtpases ◽  
Cellular Compartment ◽  
Selective Autophagy ◽  
Downstream Effector ◽  
Golgi Transport ◽  
Autophagy Pathway

Accumulation of misfolded proteins on intracellular membranes has been implicated in neurodegenerative diseases. One cellular pathway that clears such aggregates is endoplasmic reticulum autophagy (ER-phagy), a selective autophagy pathway that delivers excess ER to the lysosome for degradation. Not much is known about the regulation of ER-phagy. The conserved Ypt/Rab GTPases regulate all membrane trafficking events in eukaryotic cells. We recently showed that a Ypt module, consisting of Ypt1 and autophagy-specific upstream activator and downstream effector, regulates the onset of selective autophagy in yeast. Here we show that this module acts at the ER. Autophagy-specific mutations in its components cause accumulation of excess membrane proteins on aberrant ER structures and induction of ER stress. This accumulation is due to a block in transport of these membranes to the lysosome, where they are normally cleared. These findings establish a role for an autophagy-specific Ypt1 module in the regulation of ER-phagy. Moreover, because Ypt1 is a known key regulator of ER-to-Golgi transport, these findings establish a second role for Ypt1 at the ER. We therefore propose that individual Ypt/Rabs, in the context of distinct modules, can coordinate alternative trafficking steps from one cellular compartment to different destinations.

scholarly journals Diversity and plasticity in Rab GTPase nucleotide release mechanism has consequences for Rab activation and inactivation

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Lars Langemeyer ◽  
Ricardo Nunes Bastos ◽  
Yiying Cai ◽  
Aymelt Itzen ◽  
Karin M Reinisch ◽  
...  
Keyword(s):  
Active Site ◽  
Free Form ◽  
Release Mechanism ◽  
Rab Gtpase ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Active Site Residues ◽  
Gtp Hydrolysis ◽  
Activation Mechanisms ◽  
Gtpase Activation

Ras superfamily GTPase activation and inactivation occur by canonical nucleotide exchange and GTP hydrolysis mechanisms. Despite conservation of active-site residues, the Ras-related Rab GTPase activation pathway differs from Ras and between different Rabs. Analysis of DENND1-Rab35, Rabex-Rab5, TRAPP-Rab1 and DrrA-Rab1 suggests Rabs have the potential for activation by distinct GDP-release pathways. Conserved active-site residues in the Rab switch II region stabilising the nucleotide-free form differentiate these pathways. For DENND1-Rab35 and DrrA-Rab1 the Rab active-site glutamine, often mutated to create constitutively active forms, is involved in GEF mediated GDP-release. By contrast, in Rab5 the switch II aspartate is required for Rabex mediated GDP-release. Furthermore, Rab1 switch II glutamine mutants refractory to activation by DrrA can be activated by TRAPP, showing that a single Rab can be activated by more than one mechanistically distinct GDP-release pathway. These findings highlight plasticity in the activation mechanisms of closely related Rab GTPases.

scholarly journals The Regulation of Rab GTPases by Phosphorylation

Biomolecules ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1340
Author(s):  
Lejia Xu ◽  
Yuki Nagai ◽  
Yotaro Kajihara ◽  
Genta Ito ◽  
Taisuke Tomita
Keyword(s):  
Small Gtpases ◽  
Guanine Nucleotide Exchange Factors ◽  
Effector Proteins ◽  
Regulatory Proteins ◽  
Rab Proteins ◽  
Rab Gtpases ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Gtpase Activating Proteins

Rab proteins are small GTPases that act as molecular switches for intracellular vesicle trafficking. Although their function is mainly regulated by regulatory proteins such as GTPase-activating proteins and guanine nucleotide exchange factors, recent studies have shown that some Rab proteins are physiologically phosphorylated in the switch II region by Rab kinases. As the switch II region of Rab proteins undergoes a conformational change depending on the bound nucleotide, it plays an essential role in their function as a ‘switch’. Initially, the phosphorylation of Rab proteins in the switch II region was shown to inhibit the association with regulatory proteins. However, recent studies suggest that it also regulates the binding of Rab proteins to effector proteins, determining which pathways to regulate. These findings suggest that the regulation of the Rab function may be more dynamically regulated by phosphorylation than just through the association with regulatory proteins. In this review, we summarize the recent findings and discuss the physiological and pathological roles of Rab phosphorylation.

scholarly journals The two TRAPP complexes of metazoans have distinct roles and act on different Rab GTPases

2017 ◽  
Vol 217 (2) ◽  
pp. 601-617 ◽  
Author(s):  
Falko Riedel ◽  
Antonio Galindo ◽  
Nadine Muschalik ◽  
Sean Munro
Keyword(s):  
Drosophila Melanogaster ◽  
Guanine Nucleotide Exchange Factors ◽  
Rab Gtpase ◽  
Rab Gtpases ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors ◽  
Core Set ◽  
Protein Particle

Originally identified in yeast, transport protein particle (TRAPP) complexes are Rab GTPase exchange factors that share a core set of subunits. TRAPPs were initially found to act on Ypt1, the yeast orthologue of Rab1, but recent studies have found that yeast TRAPPII can also activate the Rab11 orthologues Ypt31/32. Mammals have two TRAPP complexes, but their role is less clear, and they contain subunits that are not found in the yeast complexes but are essential for cell growth. To investigate TRAPP function in metazoans, we show that Drosophila melanogaster have two TRAPP complexes similar to those in mammals and that both activate Rab1, whereas one, TRAPPII, also activates Rab11. TRAPPII is not essential but becomes so in the absence of the gene parcas that encodes the Drosophila orthologue of the SH3BP5 family of Rab11 guanine nucleotide exchange factors (GEFs). Thus, in metazoans, Rab1 activation requires TRAPP subunits not found in yeast, and Rab11 activation is shared by TRAPPII and an unrelated GEF that is metazoan specific.

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