Active GTPase Pull-Down and Detection

This affinity provides a method to distinguish the transient up- or down-regulation of the active populations of GTPases from global changes in GTPase expression. These transient changes in activation could be the experimental result of exposing cells to growth factors or other small-molecule stimulators or inhibitors, or due to changes that occur during cell growth, differentiation, tumorigenesis, and metastasis.

Active GTPases interact with specific downstream effector proteins. These specific protein-protein interactions can be exploited to capture active GTPases by using the effector proteins as the bait in pull-down assays. The GTPase protein-binding domains (PBDs) of these effector proteins are expressed as functional GST-fusion proteins that can be immobilized to glutathione agarose, facilitating the capture and enrichment of the active forms of their cognate GTPases. Although effector proteins often interact with one or more active GTPase, each GTPase can be individually identified and the relative quantity determined by western blot analysis after the pull-down assay.

The GTPase pull-down assay procedure is streamlined with the Thermo Scientific Pierce Active GTPase Pull-Down and Detection Kits, which are available for Arf1, Cdc42, Rac1, Rap1, Ras and Rho small GTPases. The pull-down affinity purification step is easily performed in convenient spin columns. After washing, the bound GTPase is recovered by eluting the GST-fusion protein from the glutathione resin. The purified GTPase is detected by Western blot using a specific antibody supplied in each kit. Relative differences in active GTPase signal can be quantified by densitometry or CCD camera. The GTPase pull-down procedure is already optimized for western blot analysis using Thermo Scientific SuperSignal West Pico Chemiluminescent Substrate and HRP-conjugated secondary antibodies (available separately).

• Highly sensitive and accurate—reagents, antibodies and western blot procedures ensure accurate controls and semi-quantitative results
• Convenient—no need to express and purify your own GST-PBD fusion proteins or use expensive antibody-based affinity resins
• Easy to use—achieve immediate success in a 2-hour assay
• Efficient—spin columns separate liquid from resin to prevent sample loss and cross-contamination
• Complete—kits include reagents for affinity purification, controls, cell lysis buffer, and antibodies for western blot detection
• Validated—kits are functionally tested to ensure quality and performance
• Compatible—kits work with a variety of cell types (e.g., mouse, rat, and human)

• Follow the activation of a specific GTPase during cell differentiation
• Determine the effects of small-molecule drugs on the activation of small GTPase pathways
• Study the effects of small molecule inhibitors on GTPase activation

Performing pull-down assays with the Active GTPase Pull-Down and Detection Kits is straightforward. First, whole cell lysates are prepared from cultured cells using the lysis buffer provided in the kit. Lysate (containing active and inactive GTPase) is incubated with the GST-protein binding domain (PBD) fusion protein from the respective downstream effector protein and glutathione resin. This specific interaction enables isolation of the target active (GTP-bound) GTPase. Unbound lysate proteins, including inactive or GDP-bound GTPase, are removed using the spin columns. The active GTPase population is recovered from the glutathione resin using SDS-PAGE loading buffer and analyzed by western blot.

The effectiveness of the Active GTPase Pull-Down and Detection Kits is from a combination of the integrity of the GST-effector binding domain and the quality of the primary antibody provided in the kit. In a comparison of commercial assays available to detect active Ras, each product detects a similar activation pattern, but the Active GTPase Pull-down and Detection Kit is more sensitive than pull-down and ELISA kits from other suppliers.

Additional product data and information

• Measure activation of small GTPases via their specific downstream effectors
• Detection and localization of active GTPases in neuronal cell differentiation
• GTPase enrichment using a new active-site probe

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