GDI1 encodes a GDP dissociation inhibitor that plays an essential role in the yeast secretory pathway.

Feng

et al. 1998

MBoC

350

293

The rab11 GTPase has been localized to both the Golgi and recycling endosomes; however, its Golgi-associated function has remained obscure. In this study, rab11 function in exocytic transport was analyzed by using two independent means to perturb its activity. First, expression of the dominant interfering rab11S25N mutant protein led to a significant inhibition of the cell surface transport of vesicular stomatitis virus (VSV) G protein and caused VSV G protein to accumulate in the Golgi. On the other hand, the expression of wild-type rab11 or the activating rab11Q70L mutant had no adverse effect on VSV G transport. Next, the membrane association of rab11, which is crucial for its function, was perturbed by modest increases in GDP dissociation inhibitor (GDI) levels. This led to selective inhibition of the trans-Golgi network to cell surface delivery, whereas endoplasmic reticulum–to–Golgi and intra-Golgi transport were largely unaffected. The transport inhibition was reversed specifically by coexpression of wild-type rab11 with GDI. Under the same conditions two other exocytic rab proteins, rab2 and rab8, remained membrane bound, and the transport steps regulated by these rab proteins were unaffected. Neither mutant rab11S25N nor GDI overexpression had any impact on the cell surface delivery of influenza hemagglutinin. These data show that functional rab11 is critical for the export of a basolateral marker but not an apical marker from the trans-Golgi network and pinpoint rab11 as a sensitive target for inhibition by excess GDI.

Section: Function Of Multiple Gdi Isoformssupporting

confidence: 86%

Rab11 Is Required for Trans-Golgi Network–to–Plasma Membrane Transport and a Preferential Target for GDP Dissociation Inhibitor

Feng

et al. 1998

MBoC

350

293

Proc. Natl. Acad. Sci. U.S.A.

“…The binding of Rab proteins to the universal regulatory protein GDI is of crucial importance for Rab membrane cycling and thus for the regulation of vesicular trafficking (19). In order to exert their function, Rab proteins need to be recruited specifically to the cytosolic surface of intracellular membranes in a temporally controlled manner.…”

Section: Discussionmentioning

confidence: 99%

Posttranslational modifications of Rab proteins cause effective displacement of GDP dissociation inhibitor

Oesterlin

Goody

Itzen

2012

Intracellular vesicular trafficking is regulated by approximately 60 members of the Rab subfamily of small Ras-like GDP/GTP binding proteins. Rab proteins cycle between inactive and active states as well as between cytosolic and membrane bound forms. Membrane extraction/delivery and cytosolic distribution of Rabs is mediated by interaction with the protein GDP dissociation inhibitor (GDI) that binds to prenylated inactive (GDP-bound) Rab proteins. Because the Rab:GDP:GDI complex is of high affinity, the question arises of how GDI can be displaced efficiently from Rab protein in order to allow the necessary recruitment of the Rab to its specific target membrane. While there is strong evidence that DrrA, as a bacterially encoded GDP/GTP exchange factor, contributes to this event, we show here that posttranslational modifications of Rabs can also modulate the affinity for GDI and thus cause effective displacement of GDI from Rab:GDI complexes. These activities have been found associated with the phosphocholination and adenylylation activities of the enzymes AnkX and DrrA/SidM, respectively, from the pathogenic bacterium Legionella pneumophila. Both modifications occur after spontaneous dissociation of Rab:GDI complexes within their natural equilibrium. Therefore, the effective GDI displacement that is observed is caused by inhibition of reformation of Rab:GDI complexes. Interestingly, in contrast to adenylylation by DrrA, AnkX can covalently modify inactive Rabs with high catalytic efficiency even when GDP is bound to the GTPase and hence can inhibit binding of GDI to Rab:GDP complexes. We therefore speculate that human cells could employ similar mechanisms in the absence of infection to effectively displace Rabs from GDI.T he intracellular activity of most signaling proteins is regulated at the temporal and spatial level. In the regulation of vesicular trafficking, small Ras-like GTPases of the Rab subfamily are controlled in their distribution between the cytosol and intracellular membranes, which is in turn coupled to the binding to either GDP or GTP. Cycling between the cytosol and membranes is dependent on the activation state of the Rab protein. In the active GTP-bound form, Rabs are associated with membranes, where they interact with effector proteins that promote diverse steps in vesicular trafficking. When bound to GDP, Rabs are defined as inactive and are predominantly distributed in the cytosol bound to GDI. In order to associate with the cytosolic surface of intracellular membranes, most Rab proteins possess two hydrophobic prenyl (geranylgeranyl) moieties at their structurally flexible C terminus that are posttranslationally attached via the concerted action of Rab geranylgeranyl transferase (RabGGTase) and Rab escort protein utilizing geranylgeranyl pyrophosphate as a cosubstrate. These geranylgeranyl groups mediate stable peripheral binding of Rabs to a cognate membrane by inserting the hydrophobic anchors into the lipid bilayer (1). Activation of Rab proteins is catalyzed by GDP/GTP exchange factors...

Journal of Biological Chemistry

“…The Sec4 GTPase can cycle on and off membranes in a manner that is dependent on the nucleotide state of the Rab and its interaction with GDI (17). To determine whether the absence of clustering seen with the sec4-8 secretory vesicles correlated with a loss of Sec4 function and not with an indirect defect in the sec4-8 mutation on the functionality of the vesicles, we made use of purified recombinant Rab GDI to extract Rab GTPases from the vesicles.…”

Section: Sro7-dependent Vesicle Clustering In Vitro Requires Magnesiumentioning

confidence: 99%

In Vitro Reconstitution of Rab GTPase-dependent Vesicle Clustering by the Yeast Lethal Giant Larvae/Tomosyn Homolog, Sro7

Rossi¹,

Watson²,

Demonch³

et al. 2015

Background:The mechanism by which Rab GTPases and their effectors act in tethering is not well understood. Results: An in vitro assay was developed to study vesicle clustering by the Lgl family member Sro7. Conclusion: Clustering in vitro and in vivo depends on the conformation of the Rab GTPase and Sro7. Significance: This assay provides a new tool to dissect the role of Rab and Lgl family function.