title: Structure of the cyclic-AMP-responsive exchange factor Epac2 in its auto-inhibited state.
abstract: 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 AMP and function in the control of diverse cellular processes, including cell adhesion and insulin secretion. 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 beta-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.
authors.affiliation: Department of Physiological Chemistry and Centre for Biomedical Genetics, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
authors.forename: Holger
authors.initials: H
authors.lastname: Rehmann
authors.forename: Joost
authors.initials: J
authors.lastname: Das
authors.forename: Puck
authors.initials: P
authors.lastname: Knipscheer
authors.forename: Alfred
authors.initials: A
authors.lastname: Wittinghofer
authors.forename: Johannes L
authors.initials: JL
authors.lastname: Bos
mesh_terms: D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D000242:Cyclic AMP / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D020668:rap GTP-Binding Proteins / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; C486707:Rapgef4 protein, mouse; D000242:Cyclic AMP; D020668:rap GTP-Binding Proteins