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Structural dynamics in the activation of Epac.

Shannon M Harper1, Hans Wienk, Rainer W Wechselberger

  • 1Department of Physiological Chemistry and Centre for Biomedical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands.

The Journal of Biological Chemistry
|January 3, 2008
PubMed
Summary

Epac1 activation involves dynamic conformational changes in its cyclic nucleotide binding domain. Understanding these shifts reveals key elements for Epac1 function and regulation by cAMP.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Structural Biology

Background:

  • Epac1 is a cyclic adenosine monophosphate (cAMP)-responsive guanine nucleotide exchange factor.
  • It activates the small G-protein Rap via its catalytic domain, which is regulated by a cyclic nucleotide binding (CNB) domain.
  • Rap access to the catalytic site is inhibited by the regulatory region in the absence of cAMP.

Purpose of the Study:

  • To elucidate the activation mechanism of Epac1 by analyzing the conformational states of its CNB domain.
  • To gain direct insights into how cAMP binding triggers conformational changes and activates Epac1.
  • To identify critical elements and dynamic processes within the CNB domain essential for Epac1 activation.

Main Methods:

  • Nuclear Magnetic Resonance (NMR) spectroscopy was employed to study the CNB domain.
  • Conformational states were analyzed in the absence and presence of cAMP and its analogues.
  • cAMP antagonists were utilized to dissect the sequential conformational changes during activation.

Main Results:

  • The Epac1 CNB domain exists in an equilibrium between inactive and active conformations, shifted by cAMP binding.
  • cAMP binding induces significant conformational alterations in both the ligand-binding pocket and outer helical segments.
  • The superactivator 8-pCPT-2'-O-Me-cAMP elicits similar conformational changes to cAMP but exhibits distinct internal mobility patterns, highlighting the role of dynamics.

Conclusions:

  • The study provides the first direct insights into the activation mechanism of Epac1.
  • Conformational dynamics of the CNB domain are critical for Epac1 activation by cAMP.
  • Specific structural elements and dynamic behaviors within the CNB domain are essential for Epac1's regulatory function.