Mutation of a conserved cysteine in the X-linked cone opsins causes color vision deficiencies by disrupting protein folding and stability.
OBJECTIVE
To test the effects of disruption of a conserved cysteine in the green cone opsin molecule on light-activated isomerization, transducin activation, folding, transport, and protein half-life.


METHODS
Stable cell lines were established by transfecting 293-EBNA cells with a plasmid containing wild-type or mutant (C203R, C203S, C126S, C126S/C203S) green opsin cDNA molecules. The proteins were induced by culturing the cells in the presence of cadmium chloride and analyzed by spectra, transducin activation, Western blotting, pulse-labeling with immunoprecipitation, and immunocytochemistry.


RESULTS
The C203R mutation disrupts the folding and half-life of the green opsin molecule and its abilities to absorb light at the appropriate wavelength and to activate transducin. Similar disruption of folding, half-life, and light activation occurs when Cys203 or its presumed partner for formation of a disulfide bond (Cys126) is replaced by serine residues.


CONCLUSIONS
Like rhodopsin, the folding of the cone opsins appears to be dependent on the formation of a disulfide bond between the third transmembrane helix and the second extracellular loop. Disruption of this disulfide bond represents a cause of color vision deficiencies that is unrelated to spectral shifts of the photopigment.
Kazmi
M A
MA
Department of Pediatrics, New York University Medical Center, New York 10016, USA.
Sakmar
T P
TP
Ostrer
H
H
D000595:Amino Acid Sequence; D002460:Cell Line; D003118:Color Perception; D017124:Conserved Sequence; D003545:Cysteine / Q000235:genetics*; D004355:Drug Stability; D004721:Endoplasmic Reticulum / Q000378:metabolism; D008040:Genetic Linkage; D006801:Humans; D007536:Isomerism; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D017510:Protein Folding; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D017299:Rod Opsins / Q000235:genetics* / Q000378:metabolism; D015293:Transducin / Q000502:physiology / Q000528:radiation effects; D014786:Vision Disorders / Q000235:genetics; D014960:X Chromosome
D017299:Rod Opsins; D015293:Transducin; D003545:Cysteine