Fragment‐Based Nuclear Magnetic Resonance Screen against a Regulator of G Protein Signaling Identifies a Binding “Hot Spot”

Regulator of G protein signaling (RGS) proteins have attracted attention as a result of their primary role in directing the specificity as well as the temporal and spatial aspects of G protein‐coupled receptor signaling. In addition, alterations in RGS protein expression have been observed in a number of disease states, including certain cancers. In this area, RGS17 is of particular interest. It has been demonstrated that, while RGS17 is expressed primarily in the central nervous system, it has been found to be inappropriately expressed in lung, prostate, breast, cervical, and hepatocellular carcinomas. Overexpression of RGS17 leads to dysfunction in inhibitory G protein signaling and an overproduction of the intracellular second messenger cAMP, which in turn alters the transcription patterns of proteins known to promote various cancer types. Suppressing RGS17 expression with RNA interference (RNAi) has been found to decrease tumorigenesis and sufficiently prevents cancer cell migration, leading to the hypothesis that pharmacological blocking of RGS17 function could be useful in anticancer therapies. We have identified small‐molecule fragments capable of binding the RGS homology (RH) domain of RGS17 by using a nuclear magnetic resonance fragment‐based screening approach. By chemical shift mapping of the two‐dimensional 15N,1H heteronuclear single quantum coherence (HSQC) spectra of the backbone‐assigned 15N‐labeled RGS17‐RH, we determined the fragment binding sites to be distant from the Gα interface. Thus, our study identifies a putative fragment binding site on RGS17 that was previously unknown. Altered expression of RGS17 leads to dysfunction in G protein signaling, eventually altering the transcription of cancer‐promoting proteins. Therefore, inhibiting RGS17 has potential as an anticancer therapy. We used an NMR FBLD approach to identify fragments capable of binding RGS17. Chemical‐shift mapping of the 15N/1H HSQC spectra of 15N‐labeled RGS17‐RH identified a previously unknown putative fragment binding site on RGS17.