The clustering of components of a signaling pathway at a specific subcellular location raises the local concentration of the appropriate messengers and serves to amplify the signal. The cAMP dependent-protein kinase (PKA) pathway is regulated by compartmentalization of its components. A-kinase anchoring proteins (AKAPs) tether PKA to specific subcellular sites, thus presumably increasing substrate specificity. Phosphorylation of the type II regulatory subunit of PKA (RII) increases its affinity for AKAPs in vitro (1). The purpose of this study was to investigate whether altering the phosphorylation state of RII in live cells changes its affinity for an AKAP. Specifically, we investigated the binding kinetics between Ht31, a peptide containing the PKA binding portion of an AKAP from human thyroid (2), and RII, in response to PKA activators or inhibitors.Fluorescence resonance energy transfer (FRET) was used to monitor binding events between RII and the catalytic subunit (C) of PKA, Ht31, or Ht31P, a mutated form of Ht31 which does not bind RII.
Spectral wide-field microscopic fluorescence resonance energy transfer imaging in live cells
