The present invention relates to fusion proteins for the expression of G-protein coupled receptor proteins (GPCR) with the fusion partners, as inserted fragments, from mammalian cells. The fusion partners are from a fragment of APJ protein (“the APJ protein fragment”) or a fragment with homology of more than 90% similarity to the APJ protein fragment; or a fragment of RGS16 protein (the “RGS16 protein fragment”) or a fragment with homology of more than 90% similarity to the RGS16 protein fragment; or the fragment of DNJ protein (the “DNJ protein fragment”) or a fragment with homology of more than 90% similarity to DNJ protein fragment. The fusion expression of GPCR with the above mentioned fusion partners can improve the protein yield and stability when purified from cells. Therefore, these fusion protein partners can be widely used for the study of GPCR proteins.