♦ See referenced article, J. Biol. Chem. 2011, 286, 17889–17897
Exchange proteins directly activated by cAMP (Epacs) are important signaling factors that regulate a wide range of cellular functions, including cell adhesion, exocytosis, and apoptosis. Although several successful crystallographic analyses have been done on Epacs, the highly dynamic structure of this multidomain protein has made it difficult to develop a thorough structural understanding of its mechanism of activation. In this Paper of the Week, Sheng Li and colleagues use a powerful mass spectrometric approach to study the protein's dynamics and the conformational changes associated with Epac2 activation upon binding to cAMP. The technique, amide hydrogen/deuterium exchange mass spectrometry (DXMS), allowed the researchers to determine how cAMP gains access to a ligand binding site that appeared to be inaccessible in a previously solved crystal structure. The results suggest that cAMP-induced activation is mediated by a major hinge motion that exposes a second cAMP binding site. This paper represents an elegant use of DXMS to investigate the activation mechanism of this highly dynamic protein and provides key insights that complement prior biophysical studies.
cAMP-induced conformational changes in Epac2 revealed by DXMS.