Kaylor Joanna J, Xu Tongzhou, Ingram Norianne T, Tsan Avian, Hakobyan Hayk, Fain Gordon L, Travis Gabriel H
Jules Stein Eye Institute, University of California Los Angeles School of Medicine, Los Angeles, California, 90095, USA.
Molecular, Cellular and Integrative Physiology Graduate Program, University of California Los Angeles School of Medicine, Los Angeles, California, 90095, USA.
Nat Commun. 2017 May 4;8(1):16. doi: 10.1038/s41467-017-00018-4.
The light absorbing chromophore in opsin visual pigments is the protonated Schiff base of 11-cis-retinaldehyde (11cRAL). Absorption of a photon isomerizes 11cRAL to all-trans-retinaldehyde (atRAL), briefly activating the pigment before it dissociates. Light sensitivity is restored when apo-opsin combines with another 11cRAL to form a new visual pigment. Conversion of atRAL to 11cRAL is carried out by enzyme pathways in neighboring cells. Here we show that blue (450-nm) light converts atRAL specifically to 11cRAL through a retinyl-phospholipid intermediate in photoreceptor membranes. The quantum efficiency of this photoconversion is similar to rhodopsin. Photoreceptor membranes synthesize 11cRAL chromophore faster under blue light than in darkness. Live mice regenerate rhodopsin more rapidly in blue light. Finally, whole retinas and isolated cone cells show increased photosensitivity following exposure to blue light. These results indicate that light contributes to visual-pigment renewal in mammalian rods and cones through a non-enzymatic process involving retinyl-phospholipids.It is currently thought that visual pigments in vertebrate photoreceptors are regenerated exclusively through enzymatic cycles. Here the authors show that mammalian photoreceptors also regenerate opsin pigments in light through photoisomerization of N-ret-PE (N-retinylidene-phosphatidylethanolamine.
视蛋白视觉色素中的光吸收发色团是11-顺式视黄醛(11cRAL)的质子化席夫碱。光子的吸收使11cRAL异构化为全反式视黄醛(atRAL),在色素解离之前短暂激活色素。当脱辅基视蛋白与另一种11cRAL结合形成新的视觉色素时,光敏感性得以恢复。atRAL向11cRAL的转化是通过邻近细胞中的酶途径进行的。在这里,我们表明蓝光(450纳米)通过光感受器膜中的视黄基磷脂中间体将atRAL特异性地转化为11cRAL。这种光转化的量子效率与视紫红质相似。光感受器膜在蓝光下比在黑暗中更快地合成11cRAL发色团。活小鼠在蓝光下视紫红质再生更快。最后,整个视网膜和分离的视锥细胞在暴露于蓝光后显示出光敏感性增加。这些结果表明,光通过涉及视黄基磷脂的非酶过程促进哺乳动物视杆和视锥细胞中的视觉色素更新。目前认为脊椎动物光感受器中的视觉色素仅通过酶循环再生。在这里,作者表明哺乳动物光感受器也通过N-视黄基磷脂酰乙醇胺(N-retinylidene-phosphatidylethanolamine)的光异构化在光中再生视蛋白色素。