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Title
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Structure and regulation of the cAMP-binding domains of Epac2.
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Authors
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H.Rehmann,
B.Prakash,
E.Wolf,
A.Rueppel,
J.de Rooij,
J.L.Bos,
A.Wittinghofer.
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Ref.
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Nat Struct Biol, 2003,
10,
26-32.
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PubMed id
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Abstract
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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.
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