RIalpha subunit of PKA: a cAMP-free structure reveals a hydrophobic capping mechanism for docking cAMP into site B.
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.
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA.
Jian
J
Wu
Simon
S
Brown
Nguyen-Huu
NH
Xuong
Susan S
SS
Taylor
D000495:Allosteric Site; D001665:Binding Sites; D018360:Crystallography, X-Ray; D000242:Cyclic AMP / Q000737:chemistry* / Q000378:metabolism; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry*; D006152:Cyclic GMP / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D017353:Gene Deletion; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D008024:Ligands; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D006152:Cyclic GMP