High-level inducible expression of visual pigments in transfected cells

A method for high-level expression of a functionally active, recombinant human red cone opsin was developed by adding the coding sequence for the C-terminal epitope of bovine rhodopsin onto the C terminus of the cone opsin and cloning the resulting construct into the vector pMEP4β. The recombinant pMEP4β vector was transfected stably into 293-EBNA cells, and expression of the cone opsin was induced by the addition of CdCl₂ into the medium. The recombinant cone opsin was reconstituted with 11-cis retinal and purified by immunoaffinity chromatography. Spectral analysis prior to and following photobleaching confirmed its identity as a red cone opsin. The protein was targeted to the cell membrane and activated bovine transducin.