5-adenosine monophosphate promotes signal adaptation in PKA signaling.

Abstract

Protein Kinase A (PKA) plays a central role in several cellular processes and its activity is tightly regulated by 2nd messenger 3,5-cyclic adenosine monophosphate (cAMP)-signaling. While the role of cAMP in PKA activation is well established, the significance of its hydrolysis end-product, 5-adenosine monophosphate (AMP) is poorly understood. AMP is generated upon hydrolysis of cAMP bound to the PKA regulatory subunits (RIα) catalyzed by phosphodiesterases. All components of the cAMP-PKA signaling pathway that include PDEs are compartmentalized into signalosomal units. Our research has shown that PDEs in proximity with PKA RIα in signalosomes lead to formation of a signal termination complex of PDEs and RIα, that facilitates cAMP substrate channeling from the PKA binding site to the PDE catalytic site. In contrast to the long held view that AMP diffused away from the PKA signalosome following cAMP hydrolysis, AMP is a regulatory end-product of each round of PKA activation and termination. Here we report high resolution structures of the AMP bound conformations of RIα and PDE8A catalytic domain (PDE8c) by cryo-EM. We have further captured AMP-bound end-state signal termination complex of PDE8c with RIα, by orthogonal electron microscopy screening, amide hydrogen/deuterium exchange mass spectrometry. Our results describe an undiscovered active role of AMP in signal termination and adaptation in PKA signaling.