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Biochemistry. 2002 Dec 24;41(51):15245-52.

Conserved proline residue at position 189 in cone visual pigments as a determinant of molecular properties different from rhodopsins.

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Department of Biophysics, Graduate School of Science, Kyoto University, and Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation, Kyoto 606-8502, Japan.


To identify the amino acid residue(s) responsible for the difference in the molecular properties between rod and cone pigments, we have prepared chicken green mutants where each of the residues (Val77, Gly144, and Pro189) completely conserved in the cone pigments was replaced with the residue in the rod pigment rhodopsin. Among the mutants, the P189I mutant showed an expression level in cultured HEK293 cells and a thermal stability higher than did the wild-type chicken green. The mutation caused a reduced decay rate of the meta II intermediate, while the mutation of the wild-type chicken rhodopsin at position 189 (I189P) resulted in an increased decay rate. The additional mutation at position 122, the previously reported site where the amino acid residue is one of the determinants of the meta II decay rate, converted the meta II decay rate into that observed in the wild-type chicken rhodopsin. These results suggest that the difference in the meta II decay rate between the chicken green and rhodopsin is due to the difference in the amino acid residues at positions 189 and 122. The completely conserved nature of proline at position 189 could provide a clue to the molecular evolution of the pigments.

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