Abstract
A-kinase anchoring proteins (AKAPs) include a family of scaffolding proteins that target protein kinase A (PKA) and other signaling proteins to cellular compartments and thereby confine the activities of the associated proteins to distinct regions within cells. AKAPs bind PKA directly. The interaction is mediated by the dimerization and docking domain of regulatory subunits of PKA and the PKA-binding domain of AKAPs. Analysis of the interactions between the dimerization and docking domain and various PKA-binding domains yielded a generalized motif allowing the identification of AKAPs. Our bioinformatics and peptide array screening approaches based on this signature motif identified GSKIP (glycogen synthase kinase 3beta interaction protein) as an AKAP. GSKIP directly interacts with PKA and GSK3beta (glycogen synthase kinase 3beta). It is widely expressed and facilitates phosphorylation and thus inactivation of GSK3beta by PKA. GSKIP contains the evolutionarily conserved domain of unknown function 727. We show here that this domain of GSKIP and its vertebrate orthologues binds both PKA and GSK3beta and thereby provides a mechanism for the integration of PKA and GSK3beta signaling pathways.
Highlights
A-kinase anchoring proteins (AKAPs)3 are a family of scaffoldingproteinscharacterizedbytheabilitytobindcAMPdependent protein kinase (protein kinase A (PKA))
The PKA holoenzyme consists of a dimer of regulatory RI or RII subunits and two catalytic subunits, each bound to one R subunit
GSKIP and its vertebrate and invertebrate orthologues from fungi to Homo sapiens contain the evolutionarily conserved domain of unknown function 727 (DUF727), which we show here to interact with RII subunits in the vertebrate orthologues, conferring an AKAP function
Summary
AKAP220 and MAP2 (microtubule-associated protein 2) each recruit PKA and GSK3 and facilitate PKA phosphorylation of GSK3 [17, 18]. The phosphorylation by PKA appears to require binding of both PKA and GSK3 to the respective AKAP [13, 19]. We demonstrate that the evolutionarily conserved and widely expressed protein GSKIP [20] functions as an AKAP, recruits PKA and GSK3, and facilitates PKA phosphorylation of GSK3. GSKIP and its vertebrate and invertebrate orthologues from fungi to Homo sapiens contain the evolutionarily conserved domain of unknown function 727 (DUF727), which we show here to interact with RII subunits in the vertebrate orthologues, conferring an AKAP function. The interaction with GSK3, appears to be conserved in both invertebrates and vertebrates
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