PKA Type Ⅱα Holoenzyme Reveals a Combinatorial Strategy for Isoform Diversity

摘要

The catalytic (C) subunit of cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) is inhibited by two classes of regulatory subunits, RⅠ and RⅡ. The RⅡ subunits are substrates as well as inhibitors and do not require adenosine triphosphate (ATP) to form holoenzyme, which distinguishes them from RⅠ subunits. To understand the molecular basis for isoform diversity, we solved the crystal structure of an RⅡα holoenzyme and compared it to the RⅠα holoenzyme. Unphosphorylated RⅡα(90-400), a deletion mutant, undergoes major conformational changes as both of the cAMP-binding domains wrap around the C subunit's large lobe. The hallmark of this conformationat reorganization is the helix switch in domain A. The C subunit is in an open conformation, and its carboxyl-terminal tail is disordered. This structure demonstrates the conserved and isoform-specific features of RI and RⅡ and the importance of ATP, and also provides a new paradigm for designing isoform-specific activators or antagonists for PKA.