Dizhoor Alexander M, Woodruff Michael L, Olshevskaya Elena V, Cilluffo Marianne C, Cornwall M Carter, Sieving Paul A, Fain Gordon L
Hafter Research Laboratories, Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027, USA.
J Neurosci. 2008 Nov 5;28(45):11662-72. doi: 10.1523/JNEUROSCI.4006-08.2008.
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.
已知G90D视紫红质突变会导致人类先天性夜盲。这种突变在小鼠中也会产生类似情况，因为对于该突变杂合（D+）或纯合（D+/+）的动物的视杆细胞具有降低的暗电流和敏感性、降低的Ca(2+)以及加快的tau(REC)和tau(D)值，类似于光适应的野生型（WT）视杆细胞。我们的实验表明，G90D色素激活了级联反应，对于D+产生约130 Rh* 视杆细胞(-1)的等效背景光，对于D+/+产生890 Rh* 视杆细胞(-1)的等效背景光。G90D色素的活性物种可能是未再生的G90D视蛋白或G90D视紫红质，要么是自发激活（如Rh*），要么是其他某种形式。在脂质囊泡中添加11-顺式视黄醛，其在完整视杆细胞和视网膜外段膜中会使WT和G90D视蛋白都发生再生，但对暗适应的G90D反应的波形或敏感性没有影响，这表明活性物种不是G90D视蛋白。暗适应的G90D和WT视杆细胞的噪声谱相似，并且G90D的噪声方差远小于暴露于与G90D等效光强度大致相同的背景光下的WT视杆细胞，这表明Rh*不是活性物种。我们假设G90D视紫红质会发生分子构象的自发变化，从而以低增益激活转导级联反应。我们的实验首次表明，与11-顺式发色团结合的视紫红质分子的突变形式能够以足够大的速率自发刺激视觉级联反应，从而导致视觉功能障碍。
