AKAP7

AKAP7 (AKAP15/AKAP18) is an A-kinase anchoring protein that tethers PKA—and PKC—to defined subcellular sites to enable spatially restricted phosphorylation of ion channels and Ca2+-handling proteins (PMID:11733497, PMID:9748250, PMID:22670899). It anchors PKA to skeletal muscle L-type Ca2+ channels through a leucine-zipper interaction with the CaV1.1 alpha1 C-terminus, where disrupting this interaction blocks voltage-dependent channel potentiation (PMID:11733497), and to brain Nav1.2 sodium channels by binding the intracellular I-II loop, positioning PKA at defined serine sites whose phosphorylation is gated by prior PKC modification (PMID:9748250, PMID:12359152). PKA recruitment is mediated by a PKA-binding domain that contacts the RIIα D/D domain through anchor points flanking the core binding helix (PMID:27102985). Beyond scaffolding, the central 2H phosphoesterase domain of long isoforms binds AMP and functions as a 2',5'-phosphodiesterase that degrades the 2-5A activators of RNase L, an activity abolished by the H185R mutation and dependent on cytoplasmic localization for antiviral function (PMID:18082768, PMID:24987090). In the heart, long isoforms (AKAP7γ/δ) scaffold PKA together with the deubiquitinase USP4 at sarcomere Z bands via the phosphoesterase domain; anchored PKA phosphorylates USP4 at Ser829 to stimulate its deubiquitinase activity and promote SERCA2-mediated SR Ca2+ reuptake (PMID:40449590). In the brain, the AKAP7/PKA complex in dentate granule cell mossy fibers is required for cAMP-dependent presynaptic LTP and pattern-separation behavior (PMID:27911261). Notably, global AKAP7 deletion leaves β-adrenergic Ca2+ handling in mouse ventricular cardiomyocytes intact, indicating its cardiac role is context- and isoform-specific rather than essential for canonical β-adrenergic Ca2+ regulation (PMID:23035250).

1. 1998 High

   Established that AKAP7 physically links PKA to voltage-gated sodium channels, defining its role as a channel-targeting anchor.

   Evidence Co-purification, reciprocal Co-IP, mass spectrometry, and in vitro PKA phosphorylation of Nav1.2 from rat brain

   PMID:9748250

   Open questions at the time

   • Did not map the channel-binding interface
   • Functional consequence for channel gating not yet defined
2. 2001 High

   Showed that AKAP7 anchoring of PKA to L-type Ca2+ channels is functionally required for channel modulation, linking the scaffold directly to channel physiology.

   Evidence Leucine-zipper disruption mutagenesis with electrophysiology in skeletal muscle cells

   PMID:11733497

   Open questions at the time

   • Whether the same LZ motif targets other channel types not addressed
   • Structural basis of LZ recognition not resolved
3. 2002 High

   Defined the sodium-channel binding site and revealed convergent PKC/PKA multi-site regulation gated by AKAP7-anchored kinase positioning.

   Evidence Loop I-II interaction mapping, serine site-directed mutagenesis, heterologous electrophysiology

   PMID:12359152

   Open questions at the time

   • In vivo relevance of multi-site gating not established
   • Stoichiometry of PKC/PKA co-anchoring unknown
4. 2007 High

   Discovered an unanticipated enzymatic identity for the AKAP18δ central domain as a nucleotide-binding 2H phosphoesterase, beyond pure scaffolding.

   Evidence Bioinformatics and X-ray crystallography with AMP/CMP co-crystallization

   PMID:18082768

   Open questions at the time

   • Catalytic substrate in cells not yet identified
   • Physiological role of nucleotide binding undefined at this stage
5. 2012 High

   Tested whether AKAP7 is required for cardiac Ca2+ handling and found it dispensable for β-adrenergic regulation, bounding its cardiac function.

   Evidence Global AKAP7 knockout mouse with patch clamp, Ca2+ imaging, and substrate phospho-immunoblots

   PMID:23035250

   Open questions at the time

   • Possible redundancy with other AKAPs not excluded
   • Isoform- or microdomain-specific roles not resolved by global deletion
6. 2012 Medium

   Extended AKAP7 scaffolding to PKC, showing it constrains kinase mobility and enhances substrate phosphorylation.

   Evidence SPR, pulldowns, FRET activity reporter, and FRAP imaging

   PMID:22670899

   Open questions at the time

   • Single-lab functional readouts
   • In vivo PKC substrates of the AKAP7/PKC complex not identified
7. 2014 High

   Assigned a catalytic antiviral function to the phosphoesterase domain as a 2',5'-PDE that destroys RNase L activators, with localization gating activity.

   Evidence In vitro 2-5A degradation, H185R mutagenesis, viral complementation in macrophages and mice, immunofluorescence

   PMID:24987090

   Open questions at the time

   • How nuclear full-length AKAP7 is excluded from cytoplasmic antiviral function unclear
   • Endogenous regulation of this activity in human cells not defined
8. 2016 High

   Resolved how AKAP7 engages PKA, defining anchor points outside the canonical helix required for RIIα binding.

   Evidence Crystal structure of AKAP18β PKA-binding domain with RIIα D/D, with in vitro and cell-based validation

   PMID:27102985

   Open questions at the time

   • RI subunit selectivity not addressed
   • Whether anchor points are regulated dynamically unknown
9. 2016 High

   Demonstrated a required physiological role for AKAP7 in presynaptic plasticity and behavior, placing the scaffold in cAMP-dependent LTP.

   Evidence Dentate granule cell-specific conditional knockout with LTP electrophysiology and pattern separation behavior

   PMID:27911261

   Open questions at the time

   • Presynaptic PKA substrates mediating the LTP defect not identified
   • Molecular targeting of AKAP7 at mossy fiber terminals unresolved
10. 2022 Medium

    Showed AKAP7γ is dynamically mobile and that PKA activation increases its mobility, offering a mechanism for spatial spread of β-adrenergic signaling.

    Evidence FRAP and saponin permeabilization wash-out of GFP-AKAP7γ in rabbit cardiomyocytes

    PMID:35620477

    Open questions at the time

    • Functional consequence of mobility for Ca2+ handling inferred, not demonstrated
    • Single-lab live-cell assay
11. 2025 High

    Linked AKAP7 long isoforms to SR Ca2+ reuptake via a Z-band complex in which anchored PKA activates USP4 deubiquitinase, integrating scaffolding with ubiquitin signaling.

    Evidence BioID proximity proteomics, Co-IP, in vitro PKA phosphorylation, pSer829 antibody, AKAP7 KO mouse, PKA inhibition, calcium flux

    PMID:40449590

    Open questions at the time

    • USP4 deubiquitination substrates controlling SERCA2 not identified
    • Reconciliation with the dispensable Ca2+-handling phenotype of global KO not fully addressed

• How AKAP7 isoform diversity, subcellular localization, and dual scaffolding/enzymatic activities are coordinated to select specific substrates in each tissue remains unresolved.
• No unified model linking phosphoesterase catalysis to anchoring function
• Tissue-specific isoform targeting determinants not mapped