CHARACTRIZATION OF RGS ACTIVITY AND SPECIFICITY DETERMINANTS TOWARDS G-PROTEINS

Background: RGS proteins play a critical role in many G protein-dependent signaling pathways. The biological activity of RGS proteins is to turn off heterotrimeric G proteins, thereby determining the lifetime of the activated G-protein molecular switch. RGS proteins recognize specific and individual G proteins, but previous studies have not identified the full complement of residues that are responsible for this specificity.

Purpose and methods: We extrapolated from a quantitative analysis of crystallographic complexes of G-alpha subunits with RGS proteins to identify the residues responsible for specificity in all 20 members of the RGS family. We further analyzed available 3D structures to better understand the role of specificity-determining residues.

Results: Our computational map predicts the activity of previously uninvestigated RGS proteins, and maps the residues that encode for this specificity. In addition, we compared the interactions of G-alpha subunits with representatives of additional interactions partners. Thus, we identified amino acids that contribute to interactions with all or most of these protein partners, and amino acids that contribute only to interactions with a particular partner.

Conclusion: Our results enable to better understand how substitution of RGS residues with different physic-chemical properties can determine RGS activity and specificity. Furthermore, our work identified selective residues in G-alpha subunits that differentiate between G-protein activation states and alternative partners. These results will be used to redesign RGS proteins and G-proteins with different specificities, which in turn can be used to investigate the interactions of these proteins in cells and tissues.