Sarma Ganapathy N, Moody Issa S, Ilouz Ronit, Phan Ryan H, Sankaran Banumathi, Hall Randy A, Taylor Susan S
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.
Protein Sci. 2015 Jan;24(1):105-16. doi: 10.1002/pro.2593. Epub 2014 Dec 5.
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激酶锚定蛋白（AKAPs）在空间和时间上调节环磷酸腺苷（cAMP）依赖性蛋白激酶（PKA）信号传导。双特异性AKAP2（D-AKAP2/AKAP10）与PKA的RI和RII调节亚基具有高亲和力结合，并通过PDZ结构域蛋白锚定到转运蛋白上。在此，我们描述了D-AKAP2与两个相互作用伙伴形成的复合物的结构，以及一个原本无序的片段如何向PKA呈现α螺旋并向PDZK1呈现β链的确切机制。这两个基序形成了一个多价支架，并展示了PKA信号传导如何与转运蛋白的调节相联系。D-AKAP2与PKA二元复合物的形成是与PDZK1进行高亲和力相互作用的重要第一步，该结构揭示了理解这一现象的重要线索。与许多其他AKAPs不同，D-AKAP2不直接与膜蛋白相互作用。相反，D-AKAP2的C末端促进了这种相互作用，该末端包含两个结合基序——D-AKAP2AKB和PDZ基序——它们由一个短连接子连接，并且只有在与各自的伙伴信号蛋白结合时才会变得有序。D-AKAP2AKB与R亚基的D/D结构域结合，C末端的PDZ基序与一个PDZ结构域（来自PDZK1）结合，该结构域作为连接转运蛋白的桥梁蛋白。该结构还为D-AKAP2为何会表现出与两种PKA亚型不同的结合模式这一基本问题提供了见解。
