G protein-coupled receptors (GPCRs) are seven transmembrane proteins, which play an essential role in transmitting various extracellular signals into cells. For functional and structural analysis of GPCRs, it is necessary to produce active GPCRs in high quantities with outstanding purity. Fortunately, earlier baculovirus expression vector system has been reported as a proven functional GPCR mass-production tool. Therefore, in this study, we selected Bombyx mori allatostatin-C neuropeptide receptor BNGR-A1 as a GPCR reporter protein, which has been already proved successful binding of ligand. We confirmed its expression profile in various silkworm tissues and cell lines and then verified its plasma membrane subcellular localization in cultured silkworm BmN4 cells. In addition, we constructed recombinant baculoviruses for BNGR-A1, its ligand allatostatin-C (BmAST-C) and related eight G proteins (Gs, G12, Gα4, Gq, Gβ2, Gβ3, Gβ5 and Gγ) and subsequently monitored the extracellular or intracellular expression of BNGR-A1 by co-infection with its ligand and cognate G proteins-expressing viruses. It is interesting to observe that different combinations of G proteins could result in changes or even undetectable of final yields of BNGR-A1, suggesting the essential roles of G proteins involved in the GPCR expression or stabilization. The present study demonstrated that co-infection of recombinant viruses expressing Gα4β3γ trimer enhanced the production of BNGR-A1 on BV fractions. To our knowledge, this is a fine strategy for identifying the specific G protein partner responsible for certain GPCR of interest. These studies would provide a novel idea for improving GPCR expression in the silkworm by baculovirus expression vector system.
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