Expression, purification, and preliminary X-ray crystallographic analysis of the complex of G_αi3-RGS5 from human with GDP/Mg ²⁺/AlF₄^-

Regulator of G-protein signaling 5 (RGS5), an inhibitor of Gq and Gi activation, is a member of the small RGS protein subfamily. However, despite significant process in the investigation of RGS5, no structure is yet available. In order to elucidate the mechanism of the RGS5 in G protein signaling pathway, we have overexpressed the RGS5 and G_i₃ from human in Escherichia coli and crystallized the complex of RGS5 and Gαi₃ proteins with GDP/Mg²⁺/AlF₄^- at 3.0 Å resolution using a synchrotron radiation source. The complex crystals belong to the tetragonal space group P4₁2₁2 or P4₃2 ₁2, with unit cell parameters a=b=95.9 Å, and c=138.8 Å. Assuming one complex protein in the crystallographic asymmetric unit, the calculated Matthews parameter (V_M) is 2.57 ų/Da and solvent content is 52.2%.