Night blindness and the mechanism of constitutive signaling of mutant G90D rhodopsin.
The G90D rhodopsin mutation is known to produce congenital night blindness in humans. This mutation produces a similar condition in mice, because rods of animals heterozygous (D+) or homozygous (D+/+) for this mutation have decreased dark current and sensitivity, reduced Ca(2+), and accelerated values of tau(REC) and tau(D), similar to light-adapted wild-type (WT) rods. Our experiments indicate that G90D pigment activates the cascade, producing an equivalent background light of approximately 130 Rh* rod(-1) for D+ and 890 Rh* rod(-1) for D+/+. The active species of the G90D pigment could be unregenerated G90D opsin or G90D rhodopsin, either spontaneously activated (as Rh*) or in some other form. Addition of 11-cis-retinal in lipid vesicles, which produces regeneration of both WT and G90D opsin in intact rods and ROS membranes, had no effect on the waveform or sensitivity of dark-adapted G90D responses, indicating that the active species is not G90D opsin. The noise spectra of dark-adapted G90D and WT rods are similar, and the G90D noise variance is much less than of a WT rod exposed to background light of about the same intensity as the G90D equivalent light, indicating that Rh* is not the active species. We hypothesize that G90D rhodopsin undergoes spontaneous changes in molecular conformation which activate the transduction cascade with low gain. Our experiments provide the first indication that a mutant form of the rhodopsin molecule bound to its 11-cis-chromophore can stimulate the visual cascade spontaneously at a rate large enough to produce visual dysfunction.
Dizhoor
Alexander M
AM
Hafter Research Laboratories, Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027, USA.
Woodruff
Michael L
ML
Olshevskaya
Elena V
EV
Cilluffo
Marianne C
MC
Cornwall
M Carter
MC
Sieving
Paul A
PA
Fain
Gordon L
GL
D000818:Animals; D001224:Aspartic Acid / Q000235:genetics*; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics; D003623:Dark Adaptation / Q000235:genetics; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D005136:Eye Proteins / Q000235:genetics; D005998:Glycine / Q000235:genetics*; D007700:Kinetics; D055537:Light Signal Transduction / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009755:Night Blindness / Q000235:genetics* / Q000503:physiopathology*; D055355:Opsins / Q000235:genetics / Q000378:metabolism; D010775:Photic Stimulation / Q000379:methods; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism; D012172:Retinaldehyde / Q000494:pharmacology; D012243:Rhodopsin / Q000235:genetics*; D013057:Spectrum Analysis; D013997:Time Factors; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
D001224:Aspartic Acid; D002118:Calcium; D002352:Carrier Proteins; D005136:Eye Proteins; D005998:Glycine; D055355:Opsins; D012172:Retinaldehyde; D012243:Rhodopsin; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase