The duration and amplitude of G-protein-coupled receptor (GPCR) signaling is controlled by regulator of G-protein signaling (RGS) proteins. The 20 RGS family members act as GTPase accelerating proteins through their interaction with the Gα subunit of the Gαβγ heterotrimer. Their influence over GPCR signaling has attracted many to these proteins as advantageous therapeutic targets. The nature of the RGS structure has proven to be difficult to target with small molecules using traditional high-throughput screening methods. This chapter describes NMR methods for studying small molecule interactions on RGS4. These methods can detect ligand binding without the requirement for an effect on protein function. Furthermore, the sensitivity of NMR permits detection of weaker protein-ligand interactions, such as those found with smaller fragment compounds. Fragment-based screening may be path forward to identifying a number of active small molecules toward RGS proteins. Methods and considerations for running a fragment-based screen on RGS4 using NMR are outlined in this section.
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