Description
PKA belongs to the cAMP-dependent protein kinase (PKA) family. PKA isoforms type I and II include respective dimeric R subunits RI and RII which each produce two subunits designated RI-alpha, RI-beta, RII-alpha, and RII-beta. The catalytic subunit also consists of more than one gene product. Researchers cloned mammalian catalytic subunit C-alpha, C-beta, and C-gamma cDNAs. The catalytic subunit C-beta belongs to the Ser/Thr protein kinase family. Activated by cAMP, PKA C-beta resides in the cytoplasm (inactive holoenzyme and monomeric catalytic subunit), and translocates into the nucleus (monomeric catalytic subunit). A number of inactive tetrameric holoenzymes result from the combination of homo- or heterodimers of the different regulatory subunits associated with the two catalytic subunits. cAMP causes the dissociation of the inactive holoenzyme into a dimer of regulatory subunits bound to four cAMP and two free monomeric catalytic subunits. PKA C-beta acts as a p75 neurotrophin receptor (NTR)-interacting protein, which phosphorylates p75 (NTR) at Ser304