Role of Dynamics in Cyclic-Nucleotide-Modulated Allostery

Abstract

Cyclic nucleotides such as cAMP and cGMP serve as intracellular second messengers in diverse signaling pathways that control a wide range of cellular functions. Such pathways are regulated by key cyclic nucleotide receptor proteins including protein kinase A (PKA), the exchange protein directly activated by cAMP (EPAC), the hyperpolarization-activated cyclic-nucleotide-modulated (HCN) ion channels, and protein kinase G (PKG), and malfunction of these proteins has been linked to a number of pathologies. While it is known that cyclic nucleotide binding to these proteins leads to structural perturbations that promote their activation, the role played by dynamics in auto-inhibition and cyclic-nucleotide-dependent activation is not fully understood. Therefore, in this thesis we examined dynamics within the cyclic-nucleotide receptor proteins EPAC, HCN and PKG, and found that dynamics are critical for allosteric control of activation and/or autoinhibition of all three proteins. In particular, our findings for EPAC and HCN have highlighted dynamics as a key modulator of the entropic and enthalpic components, respectively, of the free-energy landscape for cAMP-dependent allostery, while our findings for PKG have highlighted dynamics as a key determinant of the cGMP-vs.-cAMP selectivity necessary to minimize cross-talk between signaling pathways. Ultimately, we envision that the methods outlined in this thesis will reveal key differences in the regulatory mechanisms of human cyclic nucleotide receptors that can eventually be exploited in the development of novel therapeutics to selectively target a single receptor, and thus treat physiological conditions/diseases linked to malfunction of the target receptor.