Effect of cholesterol/phospholipid ratio on stimulatory GTP-binding protein function

The effect of different cholesterol/phospholipid (C/P) ratios on the coupling function between stimulatory GTP-binding protein(Gs) and adenylyl cyclase (AC) in proteoliposomes, and its relationship to the conformational change of Gs were investigated. The results showed that Gs activities of both binding GTP gamma S and stimulating adenylyl cyclase were the highest in proteoliposomes with a proper content of cholesterol similar to physiological situation while the lowest with higher cholesterol content similar to pathological situation. In addition, the conformational change of Gs in proteoliposomes was also detected by steady-state and nanosecond time-resolved fluorescence using acrylodan as a probe. It is suggested that a proper C/P ratio similar to physiological situation regulates the function of Gs by inducing a change in the physical state of lipid bilayer, which would favor the formation of a suitable conformation of Gs with higher activities of both binding GTP and stimulating adenylyl cyclase. But if C/P ratio is higher, such as in pathological situation, this is unfavorable for motion of Gs in membrane, which results in inhibition of Gs function significantly.