FIGURE 8.

The α_T* (S43N) mutant makes it possible to trap a GPCR-Gα-GTP-Gβγ complex. The activation of a GPCR (e.g. R*) promotes its interaction with a heterotrimeric G-protein (α_T-GDP-β1γ1). This results in GDP-GTP exchange on α_T, leading to a conformational change (i.e. depicted by the change from a red circle to a red square) that enables α_T-GTP to dissociate from β1γ1 and R*. Apparently, the binding of Mg²⁺ by α_T is necessary for this conformational change. Thus, the GTP-bound α_T*(S43N) mutant, that is incapable of binding Mg²⁺ and undergoing such a conformational change, is able to form a stable complex with R* and β1γ1.