Structural Basis for the 14-3-3 Protein-dependent Inhibition of the Regulator of G Protein Signaling 3 (RGS3) Function

Regulator of G protein signaling (RGS) proteins function as GTPase-activating proteins for the alpha-subunit of heterotrimeric G proteins. The function of certain RGS proteins is negatively regulated by 14-3-3 proteins, a family of highly conserved regulatory molecules expressed in all eukaryotes. In this study, we provide a structural mechanism for 14-3-3-dependent inhibition of RGS3-G alpha interaction. We have used small angle x-ray scattering, hydrogen/deuterium exchange kinetics, and Forster resonance energy transfer measurements to determine the low-resolution solution structure of the 14-3-3 zeta.RGS3 complex. The structure shows the RGS domain of RGS3 bound to the 14-3-3 zeta dimer in an as-yet-unrecognized manner interacting with less conserved regions on the outer surface of the 14-3-3 dimer outside its central channel. Our results suggest that the 14-3-3 protein binding affects the structure of the G alpha interaction portion of RGS3 as well as sterically blocks the interaction between the RGS domain and the G alpha subunit of heterotrimeric G proteins.