title: Active site coupling in PDE:PKA complexes promotes resetting of mammalian cAMP signaling.
abstract: Cyclic 3'5' adenosine monophosphate (cAMP)-dependent-protein kinase (PKA) signaling is a fundamental regulatory pathway for mediating cellular responses to hormonal stimuli. The pathway is activated by high-affinity association of cAMP with the regulatory subunit of PKA and signal termination is achieved upon cAMP dissociation from PKA. Although steps in the activation phase are well understood, little is known on how signal termination/resetting occurs. Due to the high affinity of cAMP to PKA (KD ∼ low nM), bound cAMP does not readily dissociate from PKA, thus begging the question of how tightly bound cAMP is released from PKA to reset its signaling state to respond to subsequent stimuli. It has been recently shown that phosphodiesterases (PDEs) can catalyze dissociation of bound cAMP and thereby play an active role in cAMP signal desensitization/termination. This is achieved through direct interactions with the regulatory subunit of PKA, thereby facilitating cAMP dissociation and hydrolysis. In this study, we have mapped direct interactions between a specific cyclic nucleotide phosphodiesterase (PDE8A) and a PKA regulatory subunit (RIα isoform) in mammalian cAMP signaling, by a combination of amide hydrogen/deuterium exchange mass spectrometry, peptide array, and computational docking. The interaction interface of the PDE8A:RIα complex, probed by peptide array and hydrogen/deuterium exchange mass spectrometry, brings together regions spanning the phosphodiesterase active site and cAMP-binding sites of RIα. Computational docking combined with amide hydrogen/deuterium exchange mass spectrometry provided a model for parallel dissociation of bound cAMP from the two tandem cAMP-binding domains of RIα. Active site coupling suggests a role for substrate channeling in the PDE-dependent dissociation and hydrolysis of cAMP bound to PKA. This is the first instance, to our knowledge, of PDEs directly interacting with a cAMP-receptor protein in a mammalian system, and highlights an entirely new class of binding partners for RIα. This study also highlights applications of structural mass spectrometry combined with computational docking for mapping dynamics in transient signaling protein complexes. Together, these results present a novel and critical role for phosphodiesterases in moderating local concentrations of cAMP in microdomains and signal resetting.
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore; Mechanobiology Institute, National University of Singapore, Singapore.
authors.forename: Srinath
authors.initials: S
authors.lastname: Krishnamurthy
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: Balakrishnan Shenbaga
authors.initials: BS
authors.lastname: Moorthy
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: Lim
authors.initials: L
authors.lastname: Xin Xiang
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: Lim
authors.initials: L
authors.lastname: Xin Shan
authors.affiliation: Bioinformatics Institute, A(∗)STAR, Singapore.
authors.forename: Kavitha
authors.initials: K
authors.lastname: Bharatham
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: Nikhil Kumar
authors.initials: NK
authors.lastname: Tulsian
authors.affiliation: Bioinformatics Institute, A(∗)STAR, Singapore.
authors.forename: Ivana
authors.initials: I
authors.lastname: Mihalek
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore; Mechanobiology Institute, National University of Singapore, Singapore. Electronic address: dbsgsa@nus.edu.sg.
authors.forename: Ganesh S
authors.initials: GS
authors.lastname: Anand
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000737:chemistry* / Q000378:metabolism*; D020134:Catalytic Domain; D017124:Conserved Sequence; D000242:Cyclic AMP / Q000378:metabolism*; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D062105:Molecular Docking Simulation; D015398:Signal Transduction
chemical_list: D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; C112770:PDE8A protein, human