title: Mechanism for targeting the A-kinase anchoring protein AKAP18δ to the membrane.
abstract: A-kinase anchoring proteins (AKAPs) are a family of scaffolding proteins that target PKA and other signaling molecules to cellular compartments and thereby spatiotemporally define cellular signaling events. The AKAP18 family comprises AKAP18α, AKAP18β, AKAP18γ, and AKAP18δ. The δ isoform targets PKA and phosphodiesterase PDE4D to AQP2 (aquaporin-2)-bearing vesicles to orchestrate the acute regulation of body water balance. Therefore, AKAP18δ must adopt a membrane localization that seems at odds with (i) its lack of palmitoylation or myristoylation sites that tailor its isoforms AKAP18α and AKAP18β to membrane compartments and (ii) the high sequence identity to the preferentially cytoplasmic AKAP18γ. Here, we show that the electrostatic attraction of the positively charged amino acids of AKAP18δ to negatively charged lipids explains its membrane targeting. As revealed by fluorescence correlation spectroscopy, the binding constant of purified AKAP18δ fragments to large unilamellar vesicles correlates (i) with the fraction of net negatively charged lipids in the bilayer and (ii) with the total amount of basic residues in the protein. Although distantly located on the sequence, these positively charged residues concentrate in the tertiary structure and form a clear binding surface. Thus, specific recruitment of the AKAP18δ-based signaling module to membranes such as those of AQP2-bearing vesicles must be achieved by additional mechanisms, most likely compartment-specific protein-protein interactions.
authors.affiliation: Institut für Biophysik, Johannes Kepler Universität Linz, 4040 Linz, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Horner
authors.forename: Frank
authors.initials: F
authors.lastname: Goetz
authors.forename: Robert
authors.initials: R
authors.lastname: Tampé
authors.forename: Enno
authors.initials: E
authors.lastname: Klussmann
authors.forename: Peter
authors.initials: P
authors.lastname: Pohl
mesh_terms: D054758:A Kinase Anchor Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D054754:Cyclic AMP-Dependent Protein Kinase RIIalpha Subunit / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D053835:Unilamellar Liposomes / Q000378:metabolism
chemical_list: D054758:A Kinase Anchor Proteins; D054754:Cyclic AMP-Dependent Protein Kinase RIIalpha Subunit; D050505:Mutant Proteins; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D053835:Unilamellar Liposomes; C021016:1,2-diphytanoylphosphatidylcholine; D012965:Sodium Chloride; D008239:Lysine