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Protein Sci. 2015 Jan;24(1):105-16. doi: 10.1002/pro.2593. Epub 2014 Dec 5.

D-AKAP2:PKA RII:PDZK1 ternary complex structure: insights from the nucleation of a polyvalent scaffold.

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Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, 92093-0654; Department of Pharmacology, University of California, San Diego, La Jolla, California, 92093-0654.


A-kinase anchoring proteins (AKAPs) regulate cAMP-dependent protein kinase (PKA) signaling in space and time. Dual-specific AKAP2 (D-AKAP2/AKAP10) binds with high affinity to both RI and RII regulatory subunits of PKA and is anchored to transporters through PDZ domain proteins. Here, we describe a structure of D-AKAP2 in complex with two interacting partners and the exact mechanism by which a segment that on its own is disordered presents an α-helix to PKA and a β-strand to PDZK1. These two motifs nucleate a polyvalent scaffold and show how PKA signaling is linked to the regulation of transporters. Formation of the D-AKAP2: PKA binary complex is an important first step for high affinity interaction with PDZK1, and the structure reveals important clues toward understanding this phenomenon. In contrast to many other AKAPs, D-AKAP2 does not interact directly with the membrane protein. Instead, the interaction is facilitated by the C-terminus of D-AKAP2, which contains two binding motifs-the D-AKAP2AKB and the PDZ motif-that are joined by a short linker and only become ordered upon binding to their respective partner signaling proteins. The D-AKAP2AKB binds to the D/D domain of the R-subunit and the C-terminal PDZ motif binds to a PDZ domain (from PDZK1) that serves as a bridging protein to the transporter. This structure also provides insights into the fundamental question of why D-AKAP2 would exhibit a differential mode of binding to the two PKA isoforms.


A-kinase anchoring proteins; AKAP10; D-AKAP2 specificity; PDZK1 crystal structure; PKA signaling

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