Foster K W, Saranak J, Patel N, Zarilli G, Okabe M, Kline T, Nakanishi K
Nature. 1984;311(5988):756-9. doi: 10.1038/311756a0.
Rhodopsin is a visual pigment ubiquitous in multicellular animals. If visual pigments have a common ancient origin, as is believed, then some unicellular organisms might also use a rhodopsin photoreceptor. We show here that the unicellular alga Chlamydomonas does indeed use a rhodopsin photoreceptor. We incorporated analogues of its retinal chromophore into a blind mutant; normal photobehaviour was restored and the colour of maximum sensitivity was shifted in a manner consistent with the nature of the retinal analogue added. The data suggest that 11-cis-retinal is the natural chromophore and that the protein environment of this retinal is similar to that found in bovine rhodopsin, suggesting homology with the rhodopsins of higher organisms. This is the first demonstration of a rhodopsin photoreceptor in an alga or eukaryotic protist and also the first report of behavioural spectral shifts caused by exogenous synthetic retinals in a eukaryote. A survey of the morphology and action spectra of other protists suggests that rhodopsins may be common photoreceptors of chlorophycean, prasinophycean and dinophycean algae. Thus, Chlamydomonas represents a useful new model for studying photoreceptor cells.
视紫红质是一种在多细胞动物中普遍存在的视觉色素。如果视觉色素正如人们所认为的那样有着共同的古老起源，那么一些单细胞生物可能也会使用视紫红质光感受器。我们在此表明，单细胞藻类衣藻确实会使用视紫红质光感受器。我们将其视黄醛发色团的类似物导入一个失明突变体中；恢复了正常的光行为，并且最大敏感性的颜色按照所添加视黄醛类似物的性质发生了偏移。数据表明11-顺式视黄醛是天然发色团，并且这种视黄醛的蛋白质环境与牛视紫红质中的相似，这表明与高等生物的视紫红质具有同源性。这是首次在藻类或真核原生生物中证明视紫红质光感受器，也是首次报道真核生物中由外源合成视黄醛引起的行为光谱偏移。对其他原生生物的形态学和作用光谱的调查表明，视紫红质可能是绿藻纲、原绿藻纲和甲藻纲藻类常见的光感受器。因此，衣藻是研究光感受器细胞的一个有用的新模型。
