G protein-mediated signal transduction G protein (GTP binding protein) or guanine nucleotidebinding regulatory protein, has a 7 transmembrane α-helix structure with N ending of membrane and C ending in the cell, and can bind with guanosine triphosphate (GTP) or guanosine triphosphate (GDP) (Hilf G et al., 1992) . All the members in this family have the same characters that are consisted of three diferent subunits-α, β, γ and