The testis-specific Cα2 subunit of PKA is kinetically indistinguishable from the common Cα1 subunit of PKA

Background: The two variants of the a-form of the catalytic (C) subunit of protein kinase A (PKA), designated C alpha 1 and C alpha 2, are encoded by the PRKACA gene. Whereas C alpha 1 is ubiquitous, C alpha 2 expression is restricted to the sperm cell. C alpha 1 and C alpha 2 are encoded with different N-terminal domains. In C alpha 1 but not C alpha 2 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 C alpha 1. Since C alpha 2 is not modified in the same way as C alpha 1 we tested if they have distinct biochemical activities that may be reflected in different biological properties. Results: We show that C alpha 2 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 C alpha 1. Moreover, using Surface Plasmon Resonance (SPR), we show that the interaction patterns of the physiological inhibitors RI, RII and PKI were comparable for C alpha 2 and C alpha 1. This is also the case for their potency to inhibit catalytic activities of C alpha 2 and C alpha 1. Conclusion: We conclude that the regulatory complexes formed with either C alpha 1 or C alpha 2, respectively, are indistinguishable.