Fig. 3.

Flexibility of the CNBs in the PKA R-subunits. a Different cAMP-bound R-subunits. Although each CNB domain is highly conserved, the two domains of RIIβ (Diller et al. 2001) (PDB ID 1CX4) and RIα (Su et al. 1995) (PDB ID 1RGS) are oriented in distinctly different ways. To emphasize this, the two structures have their CNB-A domains oriented the same position (white CNB-A, olive CNB-B, red PBCs). b The R:C conformation of an RIIβ-subunit complexed with a C-subunit in the holoenzyme complex (white N-lobe, olive C-lobe, teal R-subunit). c The conformational changes in the RIIβ in cAMP-bound (Active) and holoenzyme (Inactive) states. The B/C-helix in CNB-A is kinked in the cAMP-bound state and extends into a single long helix in the holoenzyme. In the presence of cAMP, RIIβ has a compact configuration with two CNB domains packed against each other. In the cAMP-free form RIIβ unfolds and forms an extensive interface with the C-subunit of PKA (Zhang et al. 2012)