PKA-type I selective constrained peptide disruptors of AKAP complexes.

A-Kinase Anchoring Proteins (AKAPs) coordinate complex signaling events by serving as spatiotemporal modulators of cAMP-dependent protein kinase activity in cells. Although AKAPs organize a plethora of diverse pathways, their cellular roles are often elusive due to the dynamic nature of these signaling complexes. AKAPs can interact with the type I or type II PKA holoenzymes by virtue of high-affinity interactions with the R-subunits. As a means to delineate AKAP-mediated PKA signaling in cells, we sought to develop isoform-selective disruptors of AKAP signaling. Here, we report the development of conformationally constrained peptides named RI-STapled Anchoring Disruptors (RI-STADs) that target the docking/dimerization domain of the type 1 regulatory subunit of PKA. These high-affinity peptides are isoform-selective for the RI isoforms, can outcompete binding by the classical AKAP disruptor Ht31, and can selectively displace RIα, but not RIIα, from binding the dual-specific AKAP149 complex. Importantly, these peptides are cell-permeable and disrupt Type I PKA-mediated phosphorylation events in the context of live cells. Hence, RI-STAD peptides are versatile cellular tools to selectively probe anchored type I PKA signaling events.

Molecular modeling of human hepatocyte PKA (cAMP-dependent protein kinase type-II) and its structure analysis.

Two binary complexes (KAP2-C subunit and cAMP-bound KAP2) were built, to investigate molecular interaction. The binding sites of KAP2 include the acidic sequence motif (Asp73-Glu87), the inhibitor peptide/linker region (Arg93-Val118), and beta barrel of cAMP-binding domains (CBD-A/B). The binding surface on the C subunit anchoring KAP2 extends to the inhibitor binding site at the active site cleft (Glu127-Glu230), Pro243-Ser252 helix and the phosphorylated activation loop (Arg194-Thr201) of the large lobe besides some sites in the small lobe. KAP2 undergoes major conformational changes in comparison of the two complexes above, especially the linker region and Met251 at Arg234-Phe252 helix as an inflexion point of the turnaround. Additionally, the interaction between KAP2 and cAMP concentrates on two catalytic motifs (FGELAL and PRAA) of phosphate binding cassette regions and the cyclic-monophosphate and ribose of cAMP. On the other hand, WAVE1 of BAD complex maybe interacts with the D/D domain of KAP2 by each of three helical motifs (Asn24-Lys46, Pro492-Val514, and Glu525-Glu547). This is helpful for our research of molecular mechanism of PKA and further analysis of BAD complex how to modulate glycolysis and apoptosis.