title: Chemical tools selectively target components of the PKA system.
abstract: BACKGROUND
  In the eukaryotic cell the cAMP-dependent protein kinase (PKA) is a key enzyme in signal transduction and represents the main target of the second messenger cAMP. Here we describe the design, synthesis and characterisation of specifically tailored cAMP analogs which can be utilised as a tool for affinity enrichment and purification as well as for proteomics based analyses of cAMP binding proteins.
  
  
  RESULTS
  Two sets of chemical binders were developed based on the phosphorothioate derivatives of cAMP, Sp-cAMPS and Rp-cAMPS acting as cAMP-agonists and -antagonists, respectively. These compounds were tested via direct surface plasmon resonance (SPR) analyses for their binding properties to PKA R-subunits and holoenzyme. Furthermore, these analogs were used in an affinity purification approach to analyse their binding and elution properties for the enrichment and improvement of cAMP binding proteins exemplified by the PKA R-subunits. As determined by SPR, all tested Sp-analogs provide valuable tools for affinity chromatography. However, Sp-8-AEA-cAMPS displayed (i) superior enrichment properties while maintaining low unspecific binding to other proteins in crude cell lysates, (ii) allowing mild elution conditions and (iii) providing the capability to efficiently purify all four isoforms of active PKA R-subunit in milligram quantities within 8 h. In a chemical proteomics approach both sets of binders, Rp- and Sp-cAMPS derivatives, can be employed. Whereas Sp-8-AEA-cAMPS preferentially binds free R-subunit, Rp-AHDAA-cAMPS, displaying antagonist properties, not only binds to the free PKA R-subunits but also to the intact PKA holoenzyme both from recombinant and endogenous sources.
  
  
  CONCLUSIONS
  In summary, all tested cAMP analogs were useful for their respective application as an affinity reagent which can enhance purification of cAMP binding proteins. Sp-8-AEA-cAMPS was considered the most efficient analog since Sp-8-AHA-cAMPS and Sp-2-AHA-cAMPS, demonstrated incomplete elution from the matrix, as well as retaining notable amounts of bound protein contaminants. Furthermore it could be demonstrated that an affinity resin based on Rp-8-AHDAA-cAMPS provides a valuable tool for chemical proteomics approaches.
authors.affiliation: Department of Biochemistry, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Bertinetti
authors.affiliation: Department of Biochemistry, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Schweinsberg
authors.affiliation: Department of Biochemistry, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Susanne E
authors.initials: SE
authors.lastname: Hanke
authors.affiliation: Biolog Life Science Institute, Flughafendamm 9a, P.O. Box 107125, Bremen, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Schwede
authors.affiliation: Department of Biochemistry, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Bertinetti
authors.affiliation: Biaffin GmbH & Co KG, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Drewianka
authors.affiliation: Biolog Life Science Institute, Flughafendamm 9a, P.O. Box 107125, Bremen, Germany.
authors.forename: Hans-Gottfried
authors.initials: HG
authors.lastname: Genieser
authors.affiliation: Department of Biochemistry, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Friedrich W
authors.initials: FW
authors.lastname: Herberg