Targeting of an a kinase-anchoring protein, AKAP79, to an inwardly rectifying potassium channel, Kir2.1

Protein kinase A (PKA) is targeted to discrete subcellular locations close to its intended substrates through interaction with A kinase-anchoring prot eins (AKAPs), Ion channels represent a diverse and important group of kinas e substrates, and it has been shown that membrane targeting of PKA through association with AKAPs facilitates PKA-mediated phosphorylation and regulat ion of several classes of ion channel. Here, we investigate the effect of A KAP79, a membrane associated multivalent-anchoring protein, upon the functi on and modulation of the strong inwardly rectifying potassium channel, Kir2 .1. Functionally, the presence of AKAP79 enhanced the response of Kir2.1 to elevated intracellular cAMP, suggesting a requirement for a pool of PKA an chored close to the channel. Antibodies directed against a hemagglutinin ep itope tag on Kir2.1 coimmunoprecipitated AKAP79, indicating that the two pr oteins exist together in a complex within intact cells. In support of this, glutathione S-transferase fusion proteins of both the intracellular N and C domains of Kir2.1 isolated AKAP79 from cell lysates, while glutathione S- transferase alone failed to interact with AKAP79. Together, these findings suggest that AKAP79 associates directly with the Kir2.1 ion channel and may serve to anchor kinase enzymes in close proximity to key channel phosphory lation sites.