Structural and dynamic determinants of inhibitor specificity among regulators of G protein signaling

• Main Author: Higgins, Colin Anthony
• Other Authors: Roman, David L.
• Format: Others
• Language: English
• Published: University of Iowa 2016
• Subjects: publicabstract; dynamic; nmr; regulator of g protein signaling; rgs4; structure; Pharmacy and Pharmaceutical Sciences
• Online Access: https://ir.uiowa.edu/etd/3099; https://ir.uiowa.edu/cgi/viewcontent.cgi?article=6443&context=etd

Regulator of G Protein Signaling 4 (RGS4) mediates motor defects in Parkinson's disease. Small molecule RGS4 inhibitors (e.g. CCG-50014) modify buried cysteine residues, but the structural and dynamic mechanisms underpinning specificity of inhibitors for RGS4 within the RGS family are poorly understood. We used NMR and other biophysical methods to examine ligand-induced structural changes and the dynamics of unliganded RGS4 and RGS8 that allow ligand binding. NMR and fluorescence spectroscopy data reveal details of the hidden, excited conformational state of RGS4 that exposes Cys148, one of the buried cysteines bound by inhibitors. We further show that specificity of RGS4 inhibitors is driven by differential accessibility of the target cysteine compared to its equivalent in RGS8. Cys148 is buried beneath the lid at the center the α4-α7 helix bundle, and this bundle is destabilized in RGS4 compared to RGS8. Notably, helix 6 is highly destabilized in RGS4 compared to RGS8 and is likely the key mediator of access to Cys148. Our findings provide key insight into the mechanism of allosteric RGS4 inhibition and show that dynamics drive inhibitory specificity among RGS proteins.