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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:

GTPases and their Regulation

GTPases and their Regulation

GTPases and their Regulation

GTPases and their Regulation

Guanine nucleotide-binding proteins (G-proteins), also known as GTPases, are a superfamily of proteins that regulate many cellular processes, such as cell signaling, vesicular transport, and the regulation of cell shape and motility. Mutation or dysfunction of these proteins can lead to disease. There are around 40,000 known G-proteins that can broadly be classified into two groups ‒ small G-proteins consisting of a single domain and large multi-domain G-proteins.
Large G-proteins,...

Activation and Inactivation of G Proteins

Activation and Inactivation of G Proteins

Heterotrimeric G proteins are guanine nucleotide-binding proteins. As the name suggests, heterotrimeric G proteins are composed of three subunits: alpha, beta, and gamma. They remain GDP-bound or GTP-bound inside the cells and switch between inactive/active states. The Gα subunit possesses the nucleotide-binding pocket that binds guanine nucleotides and switches between GDP or GTP-bound states. In contrast, the Gꞵ and Gγ subunits are always bound together with high...

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...

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Related Experiment Video

Updated: Mar 8, 2026

Presynapse Formation Assay Using Presynapse Organizer Beads and “Neuron Ball” Culture

Presynapse Formation Assay Using Presynapse Organizer Beads and “Neuron Ball” Culture

Published on: August 2, 2019

RhoGTPase Regulators Orchestrate Distinct Stages of Synaptic Development.

Samuel Martin-Vilchez¹, Leanna Whitmore¹, Hannelore Asmussen¹

¹Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, VA, United States of America.

|January 24, 2017

Summary

Small Rho GTPases regulate synaptic development and are implicated in autism. This study reveals how their regulators, GEFs, GAPs, and GDIs, control distinct stages of spine formation and maturation, balancing activity for healthy synapses.

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Area of Science:

Neuroscience
Cell Biology
Molecular Biology

Background:

Small Rho GTPases are crucial for synaptic plasticity, learning, and memory.
Dysregulation of Rho GTPases is linked to synaptic disorders like autism spectrum disorder.
Understanding upstream regulators is key to deciphering synaptic development.

Purpose of the Study:

To investigate the roles of Guanine nucleotide Exchange Factors (GEFs), GTPase Activating Proteins (GAPs), and Guanine nucleotide Dissociation Inhibitors (GDIs) in synaptic development.
To determine how these regulators sculpt specific stages of post-synaptic spine formation and maturation.
To elucidate the temporal balance of Rho GTPase activity during synapse development.

Main Methods:

Utilized molecular biology techniques to examine the function of Rho GTPase regulators.
Investigated the impact of specific GEFs, GAPs, and GDIs on synaptic spine morphology and density.
Analyzed the temporal regulation of actin polymerization and actomyosin dynamics.

Main Results:

Identified distinct roles for Rho GTPase regulators in early spine precursor formation versus later maturation.
Showed that the Rac1 GEF β-PIX promotes spine precursor formation.
Demonstrated that FRABIN (Cdc42 GEF) and OLIGOPHRENIN-1 (RhoA GAP) regulate spine precursor elongation.
Revealed that ARHGAP23 (Rac1 GAP) and RhoGDIs stabilize mature synapses by inactivating actomyosin dynamics.

Conclusions:

Specific Rho GTPase regulatory proteins (GEFs, GAPs, GDIs) differentially control distinct phases of synaptic spine development.
Combinatorial action of these regulators ensures temporal balance of Rho GTPase activity.
This precise regulation is essential for proper post-synaptic development and function.