A small molecule-regulated guanine nucleotide exchange factor.

Selective, pharmacological agents are attractive tools for studying signal transduction because they allow rapid, reversible, and dose-dependent control over intracellular protein function. However, for many targets the identification of potent and selective small molecule agonists and antagonists is a formidable challenge. An attractive strategy for circumventing this problem is to engineer a protein of interest to be sensitive to a pharmacological agent of choice. Here, we report a chemical genetic method for regulating the catalytic activity of signaling enzymes with a small molecule. This approach uses the interaction of the antiapoptotic protein Bcl-xL and a BH3 peptide as an autoinhibitory switch that can be controlled with a small molecule. We applied this strategy to the guanine nucleotide exchange factor Intersectin, which is a selective activator of the GTPase Cdc42. Replacing Intersectin's regulatory domains with the BH3 peptide/Bcl-xL binding module generated a panel of synthetic GEF constructs that can be activated with a competitive ligand. Importantly, the nucleotide exchange activities of these synthetic Intersectin constructs can be controlled in a rapid and dose-dependent manner. The modular nature of this strategy should make it useful for engineering other enzymes involved in signal transduction.