Architecture of the PKA RIIβ Holoenzyme

Abstract

How the dimeric PKA regulatory (RI and RII) subunits assemble into an inactive tetrameric complex with the catalytic subunits is very isoform specific. By solving structures of holoenzyme complexes, we now appreciate the global conformational changes that take place in each regulatory subunit as they release cAMP and wrap themselves around the catalytic subunit. By using monomeric deletion mutants we can map the novel isoform‐specific interactions of the inhibition sites in the RI and RII subunits. In parallel we have used small angle X‐ray scattering (SAXS) and small angle neutron scattering (SANS) to map the global architectures of the different conformational states. To define the shape and conformational dynamics of the RIIβ subunit, we have engineered a dimeric mutant, RIIβ(1‐280), that lacks the second cAMP binding domain. In contrast to the RIIα subunit, which forms a highly asymmetric complex, and RIα, where the tetramer is Y‐shaped, RIIβ undergoes a major conformational change. While the free RIIβ subunit forms an extended dimer, the RIIβ holoenzyme folds into a compact, globular conformation. Based on SAXS data, the properties required for this change are included within the RIIβ(1‐280) deletion mutant, and most likely relate to the linker that is disordered in the free RIIβ dimer. [Supported by NIH GM34921 to SST]