A new sensitive and subunit-selective molecular tool for investigating protein kinase A in the brain

Despite cellular complexity, a limited number of small molecules act as intracellular second messengers. Protein kinase A (PKA) is the main transducer of the information carried by cyclic adenosine monophosphate (cAMP). Recently, cellular imaging has achieved major technical advancements, although the search for more specific and sensitive low-molecular-weight probes to explore subcellular events involving second messengers is still in progress. The convergent synthesis of a novel, fluorescent small molecule comprising the cAMP structure and a rhodamine-based fluorescent residue, connected through a flexible linker, is described here. The interaction motif of this compound with PKA was investigated in silico using a blind docking approach, comparing its theoretical binding energy with the one calculated for cAMP. Moreover, the predicted pharmacokinetic properties were also computed and discussed. The new probe was tested on three areas of the mouse central nervous system (parietal cerebral cortex, hippocampus, and cerebellar cortex) with different fixation methods demonstrating remarkable selectivity towards the PKA RIα subunit. The probe showed overall better performances when compared to other commercially available fluorescent cAMP analogues, acting at lower concentrations, and providing stable labeling.