Characterization of the activation of the Rap-specific exchange factor Epac by cyclic nucleotides.

Epac1 and Epac2 are cAMP-dependent guanine nucleotide exchange factors (GEF) for the small G-proteins Rap1 and Rap2. Epac is inactive in the absence of cAMP, and binding of cAMP to a cyclic nucleotide-binding domain in the N-terminal regulatory region results in activation of the protein. The cAMP-dependent activity of Epac proteins can be analyzed by a fluorescence-based assay in vitro. These kinds of measurements can help to unravel the molecular mechanism by which cAMP binding is translated in activation of the protein. For this purpose, Epac mutants can be analyzed. In addition, the interaction of cAMP itself might be the focus of the research. Thus, modified cAMP analogs can be characterized by their ability to activate Epac. This is of particular interest for the development of Epac-specific analogs, which do not act on other cellular cAMP targets such as protein kinase A (PKA) or for the design of therapeutic agents targeting Epac.