Epac proteins (exchange proteins directly activated by cAMP) are guanine-nucleotide-exchange factors (GEFs) for the small GTP-binding proteins Rap1 and Rap2 that are directly regulated by the second messenger cyclic AMP1,2 and function in the control of diverse cellular processes, including cell adhesion and insulin secretion3. Here we report the three-dimensional structure of full-length Epac2, a 110-kDa protein that contains an amino-terminal regulatory region with two cyclic-nucleotide-binding domains and a carboxy-terminal catalytic region. The structure was solved in the absence of cAMP and shows the auto-inhibited state of Epac. The regulatory region is positioned with respect to the catalytic region by a rigid, tripartite β-sheet-like structure we refer to as the ‘switchboard’ and an ionic interaction we call the ‘ionic latch’. As a consequence of this arrangement, the access of Rap to the catalytic site is sterically blocked. Mutational analysis suggests a model for cAMP-induced Epac activation with rigid body movement of the regulatory region, the features of which are universally conserved in cAMP-regulated proteins.
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We thank T. Sixma for access to crystallization robots. We thank M. Weyand and A. Scrima for data collection and discussions. H.R. was supported by the Chemical Sciences of the Netherlands Organization for Scientific Research (NWO-CW) and is a recipient of the Otto-Hahn-Medaille of the Max-Planck-Gesellschaft. J.D. was supported by the Dutch Cancer Society.
Structure coordinates for Epac2 have been deposited in the Protein Data Bank under accession number 2BYV. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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Rehmann, H., Das, J., Knipscheer, P. et al. Structure of the cyclic-AMP-responsive exchange factor Epac2 in its auto-inhibited state. Nature 439, 625–628 (2006). https://doi.org/10.1038/nature04468