Structural dynamics and energy landscapes of G protein signaling - Title Structural dynamics and energy landscapes of G protein signaling Project Summary (Abstract) Extracellular signals like hormones and neurotransmitters use G protein coupled receptors (GPCRs) to activate multiple signaling pathways inside the cells. GPCR‐mediated signaling is involved in many physiological processes, making them attractive therapeutic targets in a broad range of disease areas that affect metabolic, nervous, cardiovascular, and immune systems, to name a few. These receptors have emerged as dynamic signaling machines controlled by their ligands, where each receptor can potentially signal through a specific or multiple heterotrimeric G proteins and each ligand is capable of signaling through multiple G proteins by binding to G protein‐selective receptors. In addition, these receptors also utilize G protein independent signaling pathways mediated by other transducer proteins like arrestins. The receptors are no longer considered simple on‐off switches due to their complex signaling profiles. The heterotrimeric G proteins have emerged as maestro controllers of receptor‐mediated signaling, capable of coupling as heterotrimers to receptors that results in G protein dissociation into G and G subunits, which can couple to downstream effectors (like adenylyl cyclases, phospholipases, ion channels, or receptor kinases) and to regulators (like RGS proteins ‐ regulators of G protein signaling). This signaling control by G proteins is orchestrated via conformational changes triggered by binding to receptors, GDP/GTP‐exchange, dissociation into G and G subunits, GTP hydrolysis, and binding to RGS proteins. G proteins have also been shown to couple with some receptors unproductively, i.e., no GDP/GTP exchange or G protein activation takes place. This proposal leverages the experimental structures available for a handful of G protein conformations and uses computational approaches like molecular dynamics to provide a mechanistic basis for G protein activation. The main objectives in this proposal aim to determine the structural determinants and thermodynamic landscapes for G protein coupling with the receptors that causes GDP release, their dissociation from the receptors after GDP‐GTP exchange, and the effect of ligands on their constitutive activity. These computational studies will be complemented with experimental biophysical and biochemical methods and will provide unprecedented mechanistic insight into molecular determinants of G protein activation.
