A-Kinase Anchoring Proteins (AKAPs)

A-kinase anchoring proteins (AKAPs) shape second-messenger signaling responses by constraining protein kinase A (PKA) at precise intracellular locations. A defining feature of AKAPs is a helical region that binds to regulatory subunits (RII) of PKA. Mining patient-derived databases has identified 42 nonsynonymous SNPs in the PKA-anchoring helices of five AKAPs. Solid-phase RII binding assays confirmed that 21 of these amino acid substitutions disrupt PKA anchoring. The most deleterious side-chain modifications are situated toward C-termini of AKAP helices. More extensive analysis was conducted on a valine-to-methionine variant in the PKA-anchoring helix of AKAP18. Molecular modeling indicates that additional density provided by methionine at position 282 in the AKAP18γ isoform deflects the pitch of the helical anchoring surface outward by 6.6°. Fluorescence polarization measurements show that this subtle topological change reduces RII-binding affinity 8.8-fold and impairs cAMP responsive potentiation of L-type Ca2+ currents in situ. Live-cell imaging of AKAP18γ V282M-GFP adducts led to the unexpected discovery that loss of PKA anchoring promotes nuclear accumulation of this polymorphic variant. Targeting proceeds via a mechanism whereby association with the PKA holoenzyme masks a polybasic nuclear localization signal on the anchoring protein. This led to the discovery of AKAP18ε: an exclusively nuclear isoform that lacks a PKA-anchoring helix. Enzyme-mediated proximity-proteomics reveal that compartment-selective variants of AKAP18 associate with distinct binding partners. Thus, naturally occurring PKA-anchoring-defective AKAP variants not only perturb dissemination of local second-messenger responses, but also may influence the intracellular distribution of certain AKAP18 isoforms.

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Granzyme B is elevated in autoimmune blistering diseases and cleaves key anchoring proteins of the dermal-epidermal junction

Scientific Reports ◽

10.1038/s41598-018-28070-0 ◽

2018 ◽

Vol 8 (1) ◽

Cited By ~ 16

Author(s):

Valerio Russo ◽

Theo Klein ◽

Darielle J. Lim ◽

Nestor Solis ◽

Yoan Machado ◽

...

Keyword(s):

Granzyme B ◽

Anchoring Proteins ◽

Autoimmune Blistering Diseases

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Localization and trafficking of cardiac voltage-gated potassium channels

Biochemical Society Transactions ◽

10.1042/bst0351069 ◽

2007 ◽

Vol 35 (5) ◽

pp. 1069-1073 ◽

Cited By ~ 8

Author(s):

D.F. Steele ◽

A. Dehghani Zadeh ◽

M.E. Loewen ◽

D. Fedida

Keyword(s):

Potassium Channels ◽

Molecular Motors ◽

Action Potentials ◽

Voltage Gated ◽

Anchoring Proteins

The proper trafficking and localization of cardiac potassium channels is profoundly important to the regulation of the regionally distinct action potentials across the myocardium. These processes are only beginning to be unravelled and involve modulators of channel synthesis and assembly, post-translational processing, various molecular motors and an increasing number of modifying enzymes and molecular anchors. The roles of anchoring proteins, molecular motors and kinases are explored and recent findings on channel internalization and trafficking are presented.

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