Structure and regulation of the cAMP-binding domains of Epac2

Nat Struct Biol. 2003 Jan;10(1):26-32. doi: 10.1038/nsb878.


Cyclic adenosine monophosphate (cAMP) is a universal second messenger that, in eukaryotes, was believed to act only on cAMP-dependent protein kinase A (PKA) and cyclic nucleotide-regulated ion channels. Recently, guanine nucleotide exchange factors specific for the small GTP-binding proteins Rap1 and Rap2 (Epacs) were described, which are also activated directly by cAMP. Here, we have determined the three-dimensional structure of the regulatory domain of Epac2, which consists of two cyclic nucleotide monophosphate (cNMP)-binding domains and one DEP (Dishevelled, Egl, Pleckstrin) domain. This is the first structure of a cNMP-binding domain in the absence of ligand, and comparison with previous structures, sequence alignment and biochemical experiments allow us to delineate a mechanism for cyclic nucleotide-mediated conformational change and activation that is most likely conserved for all cNMP-regulated proteins. We identify a hinge region that couples cAMP binding to a conformational change of the C-terminal regions. Mutations in the hinge of Epac can uncouple cAMP binding from its exchange activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Binding Sites / genetics
  • Catalytic Domain
  • Crystallography, X-Ray
  • Cyclic AMP / chemistry
  • Cyclic AMP / metabolism*
  • Cyclic AMP-Dependent Protein Kinases / chemistry
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Guanine Nucleotide Exchange Factors / chemistry*
  • Guanine Nucleotide Exchange Factors / genetics
  • Guanine Nucleotide Exchange Factors / metabolism
  • Humans
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation
  • Protein Binding
  • Protein Conformation
  • Protein Structure, Tertiary
  • Structure-Activity Relationship
  • rap GTP-Binding Proteins / chemistry
  • rap GTP-Binding Proteins / metabolism


  • Guanine Nucleotide Exchange Factors
  • RAPGEF4 protein, human
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • rap GTP-Binding Proteins