title: Unidirectional allostery in the regulatory subunit RIα facilitates efficient deactivation of protein kinase A.
abstract: The holoenzyme complex of protein kinase A is in an inactive state; activation involves ordered cAMP binding to two tandem domains of the regulatory subunit and release of the catalytic subunit. Deactivation has been less studied, during which the two cAMPs unbind from the regulatory subunit to allow association of the catalytic subunit to reform the holoenzyme complex. Unbinding of the cAMPs appears ordered as indicated by a large difference in unbinding rates from the two sites, but the cause has remained elusive given the structural similarity of the two tandem domains. Even more intriguingly, NMR data show that allosteric communication between the two domains is unidirectional. Here, we present a mechanism for the unidirectionality, developed from extensive molecular dynamics simulations of the tandem domains in different cAMP-bound forms. Disparate responses to cAMP releases from the two sites (A and B) in conformational flexibility and chemical shift perturbation confirmed unidirectional allosteric communication. Community analysis revealed that the A-site cAMP, by forming across-domain interactions, bridges an essential pathway for interdomain communication. The pathway is impaired when this cAMP is removed but remains intact when only the B-site cAMP is removed. Specifically, removal of the A-site cAMP leads to the separation of the two domains, creating room for binding the catalytic subunit. Moreover, the A-site cAMP, by maintaining interdomain coupling, retards the unbinding of the B-site cAMP and stalls an unproductive pathway of cAMP release. Our work expands the perspective on allostery and implicates functional importance for the directionality of allostery.
authors: Department of Physics, Florida State University, Tallahassee, FL 32306.|Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306.
authors: Cong
authors: C
authors: Guo
authors: Department of Physics, Florida State University, Tallahassee, FL 32306; hzhou4@fsu.edu.|Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306.
authors: Huan-Xiang
authors: HX
authors: Zhou
mesh_terms: D000494:Allosteric Regulation / Q000502:physiology; D000595:Amino Acid Sequence; D001665:Binding Sites; D020134:Catalytic Domain; D000242:Cyclic AMP / Q000378:metabolism; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases
keywords: NMR spectroscopy; cAMP; community analysis; molecular dynamics; unidirectional allostery