Structure of the cyclic-AMP-responsive exchange factor Epac2 in its auto-inhibited state


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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Structure of Epac2.
Figure 2: Anchoring points between the regulatory and catalytic regions.
Figure 3: Dependence of Rap-GEF activity (as k obs ) on cAMP concentration.
Figure 4: Comparison of Epac with cyclic-nucleotide-regulated ion channels.


  1. 1

    de Rooij, J. et al. Epac is a Rap1 guanine-nucleotide-exchange factor directly activated by cyclic AMP. Nature 396, 474–477 (1998)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Kawasaki, H. et al. A family of cAMP-binding proteins that directly activate Rap1. Science 282, 2275–2279 (1998)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Bos, J. L. Epac: a new cAMP target and new avenues in cAMP research. Nature Rev. Mol. Cell Biol. 4, 733–738 (2003)

    CAS  Article  Google Scholar 

  4. 4

    de Rooij, J. et al. Mechanism of regulation of the Epac family of cAMP-dependent RapGEFs. J. Biol. Chem. 275, 20829–20836 (2000)

    CAS  Article  Google Scholar 

  5. 5

    Boriack-Sjodin, P. A., Margarit, S. M., Bar-Sagi, D. & Kuriyan, J. The structural basis of the activation of Ras by Sos. Nature 394, 337–343 (1998)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Margarit, S. M. et al. Structural evidence for feedback activation by Ras·GTP of the Ras- specific nucleotide exchange factor SOS. Cell 112, 685–695 (2003)

    CAS  Article  Google Scholar 

  7. 7

    Herrmann, C. Ras-effector interactions: after one decade. Curr. Opin. Struct. Biol. 13, 122–129 (2003)

    CAS  Article  Google Scholar 

  8. 8

    Vijay-Kumar, S., Bugg, C. E. & Cook, W. J. Structure of ubiquitin refined at 1.8 Å resolution. J. Mol. Biol. 194, 531–544 (1987)

    CAS  Article  Google Scholar 

  9. 9

    Huang, L., Hofer, F., Martin, G. S. & Kim, S. H. Structural basis for the interaction of Ras with RalGDS. Nature Struct. Biol. 5, 422–426 (1998)

    CAS  Article  Google Scholar 

  10. 10

    Kabsch, W. & Sander, C. Dictionary of protein secondary structure: pattern recognition of hydrogen-bonded and geometrical features. Biopolymers 22, 2577–2637 (1983)

    CAS  Article  Google Scholar 

  11. 11

    Liao, Y. et al. RA-GEF, a novel Rap1A guanine nucleotide exchange factor containing a Ras/Rap1A-associating domain, is conserved between nematode and humans. J. Biol. Chem. 274, 37815–37820 (1999)

    CAS  Article  Google Scholar 

  12. 12

    Rebhun, J. F., Castro, A. F. & Quilliam, L. A. Identification of guanine nucleotide exchange factors (GEFs) for the Rap1 GTPase. Regulation of MR-GEF by M-Ras-GTP interaction. J. Biol. Chem. 275, 34901–34908 (2000)

    CAS  Article  Google Scholar 

  13. 13

    Rehmann, H. et al. Structure and regulation of the cAMP-binding domains of Epac2. Nature Struct. Biol. 10, 26–32 (2003)

    CAS  Article  Google Scholar 

  14. 14

    Rehmann, H., Rueppel, A., Bos, J. L. & Wittinghofer, A. Communication between the regulatory and the catalytic region of the cAMP-responsive guanine nucleotide exchange factor Epac. J. Biol. Chem. 278, 23508–23514 (2003)

    CAS  Article  Google Scholar 

  15. 15

    Clayton, G. M., Silverman, W. R., Heginbotham, L. & Morais-Cabral, J. H. Structural basis of ligand activation in a cyclic nucleotide regulated potassium channel. Cell 119, 615–627 (2004)

    CAS  Article  Google Scholar 

  16. 16

    Su, Y. et al. Regulatory subunit of protein kinase A: structure of deletion mutant with cAMP binding domains. Science 269, 807–813 (1995)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Kim, C., Xuong, N. H. & Taylor, S. S. Crystal structure of a complex between the catalytic and regulatory (RIα) subunits of PKA. Science 307, 690–696 (2005)

    ADS  CAS  Article  Google Scholar 

  18. 18

    Rehmann, H., Schwede, F., Doskeland, S. O., Wittinghofer, A. & Bos, J. L. Ligand-mediated activation of the cAMP-responsive guanine nucleotide exchange factor Epac. J. Biol. Chem. 278, 38548–38556 (2003)

    CAS  Article  Google Scholar 

  19. 19

    Canaves, J. M. & Taylor, S. S. Classification and phylogenetic analysis of the cAMP-dependent protein kinase regulatory subunit family. J. Mol. Evol. 54, 17–19 (2002)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Zagotta, W. N. et al. Structural basis for modulation and agonist specificity of HCN pacemaker channels. Nature 425, 200–205 (2003)

    ADS  CAS  Article  Google Scholar 

Download references


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.

Author information



Corresponding author

Correspondence to Johannes L. Bos.

Ethics declarations

Competing interests

Structure coordinates for Epac2 have been deposited in the Protein Data Bank under accession number 2BYV. Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary Notes

This file contains Supplementary Figures 1–5, Supplementary Figure Legends 1–5, Supplementary Table 1, Supplementary Methods and additional references. (PDF 2184 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

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).

Download citation


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing