The testis-specific Calpha2 subunit of PKA is kinetically indistinguishable from the common Calpha1 subunit of PKA .

Background: The two variants of the alpha-form of the catalytic (C) subunit of protein kinase A (PKA), designated Calpha1 and Calpha2, are encoded by the PRKACA gene. Whereas Calpha1 is ubiquitous, Calpha2 expression is restricted to the sperm cell. Calpha1 and Calpha2 are encoded with different N-terminal domains. In Calpha1 but not Calpha2 the N-terminal end introduces three sites for posttranslational modifications which include myristylation at Gly1, Asp-specific deamidation at Asn2 and autophosphorylation at Ser10. Previous reports have implicated specific biological features correlating with these modifications on Calpha1. Since Calpha2 is not modified in the same way as Calpha1 we tested if they have distinct biochemical activities that may be reflected in different biological properties. Results: We show that Calpha2 interacts with the two major forms of the regulatory subunit (R) of PKA, RI and RII, to form cAMP-sensitive PKAI and PKAII holoenzymes both in vitro and in vivo as is also the case with Calpha1. Moreover, using Surface Plasmon Resonance (SPR), we show that the interaction patterns of the physiological inhibitors RI, RII and PKI were comparable for Calpha2 and Calpha1. This is also the case for their potency to inhibit catalytic activities of Calpha2 and Calpha1. Conclusion: We conclude that the regulatory complexes formed with either Calpha1 or Calpha2, respectively, are indistinguishable.