Objective Using M2-Gi1α fusion protein expressed by baculovirus-Sf9 cell system to find the specific ligand for M2 receptor and detect the interaction of the two parts of the fusion protein.Methods The fused M2-Gi1α cDNAs were generated in a two-step PCR and then expressed in Sf9 cells.[3H]QNB and[35S]GTPγS binding experiments were employed to study the function of M2-Gi1α fusion protein.Results The expression level of M2-Gi1α fusion protein was 8.44±0.39 nmol·g-1 protein.The affinity of GDP to the Gi1α part changed under the affection of different ligands.The IC50 value in the appearance of acetylcholine,oxotremorine,arecoline,atropine,fangchinoline,levitimide were 21.35 μmol·L-1,23.86 μmol·L-1,11.91 μmol·L-1,0.13 μmol·L-1,1.05 μmol·L-1,1.75 μmol·L-1,and 2.5 μmol·L-1 when there was no ligand.Conclusion The M2-Gi1α fusion protein expressed in baculovirus-Sf9 cell system has pharmacological specificity for M2 receptor and the efficient coupling function between the two parts.The M2-Gi1αfusion protein is a helpful tool for detecting the new specific ligands of the M2 receptor.

Aim To generate m3AChR-G11 fusion protein in baculovirus-Sf9 cells and test the couping function,the interation and the influence factors be-tween m3AChR and G11 protein,as well as screen the specific ligands for m3AChR. Methods m3AChR-G11 fused DNA was generated through a two-step PCR and then expressed in Sf9 cells to produce fusion protein. The total concentration for membrane protein was de-tected by BCA method,[3H]QNB and [35 S]GTP?S binding experiment as perfomed to study the function of m3AChR-G11 fusion protein. Results The expression level of m3AChR-G11 was 7. 76 ? 10 -9 mol?g -1. The affinity of GDP to G11 partner changed in the presence of different muscarinic ligands. IC50 values of GDP in the presence of ACh,Pilo,CCh,MCN-A-343,Atro,4-Damp and Dafi were 82. 2,93. 70,12. 10,14. 30, 1. 93,1. 37,0. 72 ? 10 -6 mol ? L -1 respectively,and that in the absence of muscarinic was 1. 99 ? 10 -6 mol ?L-1.Concluslons The m3AChR-G11 fusion protein has the pharmacological specificity of m3 receptor and the efficient coupling interaction of the two partners. Affinity of GDP to ligand-bound fusion protein represents the species of muscarinic ligands. This is helpful in screening and detecting the new specific ligands to muscarinic receptors.