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Publication Abstract from PubMed

To provide tight spatiotemporal signaling control, the cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) holoenzyme typically nucleates a macromolecular complex or a "PKA signalosome." Using the RIIbeta holoenzyme as a prototype, we show how autophosphorylation/dephosphorylation of the RIIbeta subunit, as well as cAMP and metal ions, contribute to the dynamics of PKA signaling. While we showed previously that the RIIbeta holoenzyme could undergo a single turnover autophosphorylation with adenosine triphosphate and magnesium (MgATP) and trap both products in the crystal lattice, we asked here whether calcium could trap an ATP:RIIbeta holoenzyme since the RIIbeta holoenzyme is located close to ion channels. The 2.8A structure of an RIIbetap2:C2:(Ca2ADP)2 holoenzyme, supported by biochemical and biophysical data, reveals a trapped single phosphorylation event similar to MgATP. Thus, calcium can mediate a single turnover event with either ATP or adenosine-5'-(beta,gamma-imido)triphosphate (AMP-PNP), even though it cannot support steady-state catalysis efficiently. The holoenzyme serves as a "product trap" because of the slow off-rate of the pRIIbeta subunit, which is controlled by cAMP, not by phosphorylation of the inhibitor site. By quantitatively defining the RIIbeta signaling cycle, we show that release of pRIIbeta in the presence of cAMP is reduced by calcium, whereas autophosphorylation at the phosphorylation site (P-site) inhibits holoenzyme reassociation with the catalytic subunit. Adding a single phosphoryl group to the preformed RIIbeta holoenzyme thus creates a signaling cycle in which phosphatases become an essential partner. This previously unappreciated molecular mechanism is an integral part of PKA signaling for type II holoenzymes.

Single Turnover Autophosphorylation Cycle of the PKA RIIbeta Holoenzyme.,Zhang P, Knape MJ, Ahuja LG, Keshwani MM, King CC, Sastri M, Herberg FW, Taylor SS PLoS Biol. 2015 Jul 9;13(7):e1002192. doi: 10.1371/journal.pbio.1002192., eCollection 2015 Jul. PMID:26158466^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.