PMID: 15274925 , Related PDB id: 1RL3
Wu J, Brown S, Xuong NH, Taylor SS
RIalpha subunit of PKA: a cAMP-free structure reveals a hydrophobic capping mechanism for docking cAMP into site B.
Structure. 2004 Jun;12(6):1057-65.
In eukaryotes the primary target for cAMP, a ubiquitous second messenger, is cAMP-dependent protein kinase (PKA). Understanding how binding and release of cAMP changes the cAMP binding domains and then triggers long-range allosteric responses is an important challenge. This conformational switching requires structure solutions of cAMP binding domains in cAMP-bound and cAMP-free states. We describe for the first time a crystal structure of the cAMP binding domains of PKA type Ialpha regulatory subunit where site A is occupied by cGMP and site B is unoccupied. The structure reveals that the carboxyl terminus of domain B serves as a hydrophobic cap, locking the cyclic nucleotide via its adenine ring into the beta-barrel. In the absence of cAMP, the "cap" is released via an extension of the C-terminal helix. This simple hinge mechanism for binding and release of cAMP also provides a mechanism for allosteric communication between sites A and B.