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Rab Cascades

Rab Cascades

Rab GTPases act in a regulated cascade during membrane fusion, helping the lipid bilayers mix. The Rab family of proteins are active when bound to GTP, and inactive when bound to GDP. Hence, they act as guanine nucleotide-dependent molecular switches. Rab-GTP recognizes and binds to long or short-range tethering proteins to capture the target vesicle. These tethers coordinate with SNAREs on the vesicle and the target membrane to assemble the trans SNARE complex that locks the mixing bilayers.

Small GTPases - Ras and Rho

Small GTPases - Ras and Rho

Ras and Rho are small monomeric GTPases that act downstream of receptor tyrosine kinase (RTK) and regulate various cellular processes. These GTPases switch between active and inactive states by binding to guanine nucleotides.
Three regulatory proteins control their activity:

Rab Proteins

Rab Proteins

Rab proteins constitute the largest family of monomeric GTPases, of which 70 members are present in humans. Rab proteins and their effectors regulate consecutive stages of vesicle transport such as vesicle transport, docking, and fusion to the correct recipient membrane.
Rab proteins switch between a cytosolic, GDP-bound inactive state and a membrane-anchored, GTP-bound active state. By themselves, Rabs show slow rates of GDP/GTP exchange and GTP hydrolysis. Thus, Rab proteins are considered...

Vesicular Tubular Clusters

Vesicular Tubular Clusters

After budding out from the ER membrane, some COPII vesicles lose their coat and fuse with one another to form larger vesicles and interconnected tubules called vesicular tubular clusters or VTCs. These clusters constitute a compartment at the ER-Golgi interface known as ERGIC (Endoplasmic Reticulum Golgi Intermediate Compartment). The ERGIC is a mobile membrane-bound cargo transport system that sorts proteins secreted from ER and delivers them to the Golgi.
With the help of motor proteins such...

Coat Assembly and GTPases

Coat Assembly and GTPases

Vesicles incorporate different coat protein subunits in different cell locations, which changes the properties of the coat, such as the shape and geometry of the transport vesicles. Thus, vesicle coat proteins also play a significant role in cargo selection.
Coat assembly depends on the local availability of phosphatidylinositol phosphates or PIPs and GTP-binding proteins. Adaptor proteins, which link the coat proteins to the membrane, bind to these PIPs and play a crucial role in controlling...

SNAREs and Membrane Fusion

SNAREs and Membrane Fusion

Once a transport vesicle has recognized its target organelle, the vesicular membrane needs to fuse with the target membrane to unload the cargo. Transmembrane proteins called SNAREs present on organelle membranes and their vesicles, mediate vesicle fusion.
SNAREs exist in pairs that symmetrically interact and catalyze the fusion of the lipid bilayers in vesicle and target organelle. v-SNARE in the vesicle membrane are single polypeptide chains that bind to a complementary t-SNARE, composed of 2...

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Related Experiment Video

Updated: May 19, 2026

Affinity Precipitation of Active Rho-GEFs Using a GST-tagged Mutant Rho Protein (GST-RhoA(G17A)) from Epithelial Cell Lysates

Affinity Precipitation of Active Rho-GEFs Using a GST-tagged Mutant Rho Protein (GST-RhoA(G17A)) from Epithelial Cell Lysates

Published on: March 31, 2012

The microtubule-associated Rho activating factor GEF-H1 interacts with exocyst complex to regulate vesicle traffic.

Ritu Pathak¹, Violaine D Delorme-Walker, Michael C Howell

¹Department of Immunology and Microbial Science, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA.

Developmental Cell

|August 18, 2012

Summary

GEF-H1 depletion disrupts vesicle trafficking by affecting the exocyst complex. This study reveals GEF-H1 binds Sec5, activating RhoA for exocytosis regulation.

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Affinity Precipitation of Active Rho-GEFs Using a GST-tagged Mutant Rho Protein (GST-RhoA(G17A)) from Epithelial Cell Lysates

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Published on: March 31, 2012

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In Vitro Polymerization of F-actin on Early Endosomes

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Published on: August 28, 2017

Area of Science:

Cell Biology
Molecular Biology
Membrane Trafficking

Background:

The exocyst complex is essential for vesicle targeting and tethering to the plasma membrane, crucial for polarized membrane delivery.
Cell motility and division depend on proper exocyst function.
The precise role of Rho GTPases in exocyst-mediated vesicle targeting remains unclear.

Purpose of the Study:

To investigate the role of GEF-H1 (guanine nucleotide exchange factor for Rho proteins) in vesicle trafficking.
To elucidate the interaction between GEF-H1, exocyst components, and Rho GTPases.
To define a novel signaling pathway regulating exocytosis.

Main Methods:

Depletion of GEF-H1 to observe effects on vesicle trafficking.
Co-immunoprecipitation assays to detect direct binding between GEF-H1 and exocyst component Sec5.
Analysis of RhoA activation and exocyst assembly/localization following GEF-H1 manipulation.

Main Results:

GEF-H1 depletion significantly affects vesicle trafficking.
GEF-H1 directly binds to the exocyst component Sec5 in a Ral GTPase-dependent manner.
This interaction leads to RhoA activation, which subsequently regulates exocyst localization and exocytosis.

Conclusions:

A novel mechanism for RhoA activation is defined, initiated by RalA-Sec5 signaling.
The GEF-H1/RhoA pathway is critically involved in regulating vesicle trafficking and exocytosis.
This study clarifies the interplay between Rho GTPases and the exocyst complex in membrane dynamics.