A single amino acid substitution in rhodopsin (lysine 248----leucine) prevents activation of transducin.

In structure-function studies on bovine rhodopsin by in vitro site-specific mutagenesis, we have prepared three mutants in the cytoplasmic loop between the putative transmembrane helices E and F. In each mutant, charged amino acid residues were replaced by neutral residues: mutant 1, Glu239----Gln; mutant 2, Lys248----Leu; and mutant 3, Glu247----Gln, Lys248----Leu, and Glu249----Gln. The mutant rhodopsin genes were expressed in monkey kidney (COS-1) cells. After the addition of 11-cis-retinal to the cells, the rhodopsin mutants were purified by immunoaffinity adsorption. Each mutant gave a wild-type rhodopsin visible absorption spectrum. The mutants were assayed for their ability to stimulate the GTPase activity of transducin in a light-dependent manner. While mutants 1 and 3 showed wild-type activity, mutant 2 (Lys248----Leu) was inactive.