AKAP10

AKAP10 (D-AKAP2) is a multi-domain scaffold protein that anchors cAMP-dependent protein kinase (PKA) to specific subcellular compartments and coordinates PKA signaling with endocytic recycling and transporter regulation. Its C-terminal AKB helix binds the dimerization/docking domains of both RIα and RIIα regulatory subunits of PKA through distinct helical registers, and a redox-sensitive disulfide in RIα modulates this interaction (PMID:9326583, PMID:20159461). The tandem N-terminal RGS domains bind GTP-loaded Rab4 and Rab11 on recycling endosomes, controlling transferrin receptor trafficking and endosomal compartment morphology (PMID:19797056), while a C-terminal PDZ-binding motif recruits PDZK1 to form a ternary complex with PKA RII that couples phosphorylation to apical membrane transporter regulation in renal proximal tubule cells (PMID:14531807, PMID:25348485). Heterozygous disruption of Akap10 in mice increases cardiac myocyte sensitivity to cholinergic stimulation, causes arrhythmias, and leads to premature death, establishing AKAP10 as a critical regulator of cardiac autonomic signaling (PMID:17485678).

1. 1997 High

   The discovery that D-AKAP2 binds both RIα and RIIα via a C-terminal domain established it as the first characterized dual-specificity AKAP and raised the question of how a single helix accommodates two structurally distinct R-subunit classes.

   Evidence Yeast two-hybrid screen with RI/RII baits followed by reciprocal coprecipitation with domain truncations

   PMID:9326583

   Open questions at the time

   • Structural basis for dual specificity was unknown
   • Function of the N-terminal putative RGS domain was uncharacterized
   • Subcellular localization of full-length protein was not determined
2. 2001 High

   Localization of full-length D-AKAP2 to mitochondria and confirmation of in vivo PKA association in brain placed the scaffold at a defined organelle, but left its non-PKA functions unresolved.

   Evidence Immunocytochemistry, subcellular fractionation, and cAMP-agarose pull-down from mouse brain

   PMID:11248059

   Open questions at the time

   • Mitochondrial targeting mechanism was not identified
   • RGS domain ligands remained unknown
   • Functional consequence of mitochondrial PKA anchoring was not tested
3. 2002 High

   Biophysical mapping by deuterium exchange revealed that D-AKAP2 consists of two independently folded domains — an RGS-containing region and a PKA-binding/PDZ-motif region — establishing a modular scaffold architecture that could integrate distinct signaling inputs.

   Evidence DXMS and limited proteolysis of purified D-AKAP2

   PMID:12206784

   Open questions at the time

   • Identity of PDZ-domain binding partners was unknown
   • Whether the two domains function independently or cooperatively was unclear
4. 2003 High

   Identification of PDZK1 as a binding partner for D-AKAP2's PDZ motif explained how the scaffold positions PKA near apical membrane transporters such as NaPi-IIa, linking it to PTH-regulated phosphate transport in the kidney.

   Evidence Yeast two-hybrid, pull-down, and co-immunoprecipitation in OK cells plus immunohistochemistry of renal tissue

   PMID:14531807

   Open questions at the time

   • Whether PKA phosphorylation of NaPi-IIa is directly mediated through this complex was not shown
   • Relative contribution of NHERF-1 versus PDZK1 interaction in vivo was unresolved
5. 2007 High

   Gene-trap disruption of Akap10 in mice demonstrated that loss of the PKA-anchoring domain causes enhanced cholinergic responsiveness, cardiac arrhythmias, and premature death, providing the first in vivo evidence that AKAP10 scaffolding is essential for normal cardiac autonomic signaling.

   Evidence Gene-trap knockout mice phenotyped by ECG monitoring, contractility assays, and mESC-derived cardiomyocyte analysis

   PMID:17485678

   Open questions at the time

   • Molecular pathway downstream of PKA in cardiomyocytes was not delineated
   • Whether cardiac phenotype involves RGS-domain or PDZ-motif functions was not tested
   • Cell-type specificity of the cardiac requirement was not resolved
6. 2009 High

   The demonstration that D-AKAP2's tandem RGS domains bind GTP-Rab4 and Rab11 — an unprecedented RGS–small-GTPase interaction — and regulate endosomal recycling revealed that AKAP10 integrates PKA signaling with membrane trafficking.

   Evidence Co-immunoprecipitation, GTP-pulldown, colocalization microscopy, and RNAi knockdown with transferrin recycling assays

   PMID:19797056

   Open questions at the time

   • Whether the RGS domains possess GAP activity toward Rab4/Rab11 was not established
   • Coupling between Rab-binding and PKA-anchoring functions on the same scaffold was not tested
   • Structural basis of RGS–Rab recognition was not determined
7. 2010 High

   Crystal structures of the RIα D/D domain bound to the D-AKAP2 AKB helix resolved how dual specificity arises: the helix shifts its register compared to the RIIα complex, and a redox-sensitive disulfide in RIα modulates binding affinity, introducing a regulatory dimension to AKAP–PKA interaction.

   Evidence X-ray crystallography of RIα D/D alone and in complex with the D-AKAP2 AKB peptide

   PMID:20159461

   Open questions at the time

   • Physiological relevance of redox-regulated AKAP binding was not tested in cells
   • Whether the helical register shift alters downstream signaling output was unknown
8. 2014 High

   The ternary complex crystal structure of D-AKAP2–PKA RII–PDZK1 showed that PKA binding nucleates a polyvalent scaffold where an intrinsically disordered segment adopts both α-helical (AKB) and β-strand (PDZ ligand) conformations, and that binary PKA engagement is prerequisite for high-affinity PDZK1 recruitment, establishing an ordered assembly mechanism.

   Evidence X-ray crystallography of the reconstituted ternary complex

   PMID:25348485

   Open questions at the time

   • Whether ordered assembly occurs in vivo and is regulated by cAMP levels was not shown
   • How PKA catalytic subunit release from this ternary complex affects transporter phosphorylation was not addressed

• The relationship between AKAP10's Rab-binding and PKA-anchoring activities on the same molecule, the structural basis of RGS–Rab recognition, and the downstream PKA substrates mediating the cardiac phenotype remain unresolved.
• No structure of the RGS–Rab complex exists
• PKA substrates relevant to cardiac rhythm regulation via AKAP10 are unidentified
• Whether Rab-dependent trafficking and PKA anchoring are coordinated on the same scaffold in vivo is untested