title: D-AKAP2:PKA RII:PDZK1 ternary complex structure: insights from the nucleation of a polyvalent scaffold.
abstract: 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.
authors.affiliation: 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.
authors.forename: Ganapathy N
authors.initials: GN
authors.lastname: Sarma
authors.forename: Issa S
authors.initials: IS
authors.lastname: Moody
authors.forename: Ronit
authors.initials: R
authors.lastname: Ilouz
authors.forename: Ryan H
authors.initials: RH
authors.lastname: Phan
authors.forename: Banumathi
authors.initials: B
authors.lastname: Sankaran
authors.forename: Randy A
authors.initials: RA
authors.lastname: Hall
authors.forename: Susan S
authors.initials: SS
authors.lastname: Taylor
mesh_terms: D054758:A Kinase Anchor Proteins / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D054731:PDZ Domains; D011487:Protein Conformation; D051381:Rats
chemical_list: D054758:A Kinase Anchor Proteins; C484639:AKAP10 protein, human; D002352:Carrier Proteins; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D008565:Membrane Proteins; C484659:PDZK1 protein, human; C517836:Prkar1a protein, rat
keywords: A-kinase anchoring proteins; AKAP10; D-AKAP2 specificity; PDZK1 crystal structure; PKA signaling