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Structure of sm AKAP and its regulation by PKA ‐mediated phosphorylation
Author(s) -
Burgers Pepijn P.,
Bruystens Jessica,
Burnley Rebecca J.,
Nikolaev Viacheslav O.,
Keshwani Malik,
Wu Jian,
Janssen Bert J. C.,
Taylor Susan S.,
Heck Albert J. R.,
Scholten Arjen
Publication year - 2016
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.13726
Subject(s) - phosphorylation , chemistry , protein kinase a , biophysics , microbiology and biotechnology , biochemistry , biology
The A‐kinase anchoring protein ( AKAP ) sm AKAP has three extraordinary features; it is very small, it is anchored directly to membranes by acyl motifs, and it interacts almost exclusively with the type I regulatory subunits ( RI ) of c AMP ‐dependent kinase ( PKA ). Here, we determined the crystal structure of sm AKAP 's A‐kinase binding domain (sm AKAP ‐ AKB ) in complex with the dimerization/docking (D/D) domain of RI α which reveals an extended hydrophobic interface with unique interaction pockets that drive sm AKAP 's high specificity for RI subunits. We also identify a conserved PKA phosphorylation site at Ser66 in the AKB domain which we predict would cause steric clashes and disrupt binding. This correlates with in vivo colocalization and fluorescence polarization studies, where Ser66 AKB phosphorylation ablates RI binding. Hydrogen/deuterium exchange studies confirm that the AKB helix is accessible and dynamic. Furthermore, full‐length sm AKAP as well as the unbound AKB is predicted to contain a break at the phosphorylation site, and circular dichroism measurements confirm that the AKB domain loses its helicity following phosphorylation. As the active site of PKA 's catalytic subunit does not accommodate α‐helices, we predict that the inherent flexibility of the AKB domain enables its phosphorylation by PKA . This represents a novel mechanism, whereby activation of anchored PKA can terminate its binding to sm AKAP affecting the regulation of localized c AMP signaling events. Database Structural data are available in the PDB under accession number 5HVZ .