Related Experiment Video

Updated: Sep 26, 2026

Comparing the Affinity of GTPase-binding Proteins using Competition Assays
10:37

Comparing the Affinity of GTPase-binding Proteins using Competition Assays

Published on: October 8, 2015

SmgGDS displays differential binding and exchange activity towards different Ras isoforms

Haris G Vikis1, Scott Stewart, Kun-Liang Guan

  • 1Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan, MI 48109-0606, USA.

Oncogene
|April 12, 2002
PubMed

Insights

Small G-protein dissociation stimulator (smgGDS) interacts with specific Ras GTPase forms but doesn't activate HRas or NRas. This highlights functional differences among Ras isoforms and the importance of C-terminal regions.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Biochemistry

Background:

  • Ras family GTPases are crucial regulators of cell proliferation, differentiation, and cancer.
  • Guanine nucleotide exchange factors (GEFs) modulate Ras activity by promoting GTP/GDP exchange.
  • Identifying novel GEFs and understanding their specificities is key to deciphering Ras signaling pathways.

Purpose of the Study:

  • To identify novel guanine nucleotide exchange factors (GEFs) for HRas.
  • To characterize the interaction between HRas and small G-protein dissociation stimulator (smgGDS).
  • To investigate the functional consequences of smgGDS binding on Ras GTPase activity and specificity.

Main Methods:

  • Co-immunoprecipitation assays to study protein interactions.
  • In vitro guanine nucleotide exchange assays.
  • Site-directed mutagenesis to analyze the role of specific GTPase domains.

Main Results:

  • SmgGDS was identified as a binding partner for HRas and NRas, specifically interacting with dominant-negative and nucleotide-free forms.
  • SmgGDS did not catalyze guanine nucleotide exchange on HRas or NRas in vitro.
  • SmgGDS bound to other GTPases (KRas, Rac1, RhoA) in both active and inactive states, dependent on C-terminal poly-basic residues.
  • An HRas effector domain mutant (HRasN17G37) lost the ability to bind smgGDS.

Conclusions:

  • The C-terminal poly-basic region of small GTPases is critical for smgGDS binding and nucleotide exchange.
  • SmgGDS exhibits distinct binding and functional specificities towards different Ras and Rho family GTPases.
  • Mammalian Ras isoforms are not functionally interchangeable, with unique regulatory mechanisms governing their activity.

More Related Videos

Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding10:13

Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding

Published on: June 9, 2017

Detection of Small GTPase Prenylation and GTP Binding Using Membrane Fractionation and GTPase-linked Immunosorbent Assay13:51

Detection of Small GTPase Prenylation and GTP Binding Using Membrane Fractionation and GTPase-linked Immunosorbent Assay

Published on: November 11, 2018

Related Concept Videos

Rab Proteins01:14

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...
The Ras Gene02:38

The Ras Gene

The Ras-gene-encoded proteins are regulators of signaling pathways controlling cell proliferation, differentiation, or cell survival. The Ras-gene family in humans constitutes three primary members—the HRas, NRas, and KRas. These genes code for four functionally distinct yet closely related proteins—the HRas, NRas, KRas4A, and KRas4B. The involvement of mutant Ras genes in human cancer was first discovered in 1982 and is among the most common causes of human tumorigenesis.
Ras is a superfamily...
Rab Cascades01:25

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.
Assembly of Signaling Complexes01:30

Assembly of Signaling Complexes

Multiprotein signaling complexes are formed in a dynamic process involving protein-protein interactions at the cytoplasmic domain of transmembrane receptors or enzymatic and non-enzymatic proteins associated with the receptor. These complexes ensure the activation and propagation of intracellular signals that regulate cell functions.
Interaction domains in cell signaling
Interaction domains recognize exposed features of their binding partners containing post-translationally modified sequences,...
Small GTPases - Ras and Rho01:24

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:
Activation and Inactivation of G Proteins01:22

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 affinity and are together...