Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, 63110, United States.
Dev Biol. 2021 Jul;475:145-155. doi: 10.1016/j.ydbio.2021.03.002. Epub 2021 Mar 6.
Vertebrate rod and cone photoreceptors detect light via a specialized organelle called the outer segment. This structure is packed with light-sensitive molecules known as visual pigments that consist of a G-protein-coupled, seven-transmembrane protein known as opsin, and a chromophore prosthetic group, either 11-cis retinal ('A') or 11-cis 3,4-didehydroretinal ('A'). The enzyme cyp27c1 converts A into A in the retinal pigment epithelium. Replacing A with A in a visual pigment red-shifts its spectral sensitivity and broadens its bandwidth of absorption at the expense of decreased photosensitivity and increased thermal noise. The use of vitamin A-based visual pigments is strongly associated with the occupation of aquatic habitats in which the ambient light is red-shifted. By modulating the A/A ratio in the retina, an organism can dynamically tune the spectral sensitivity of the visual system to better match the predominant wavelengths of light in its environment. As many as a quarter of all vertebrate species utilize A, at least during a part of their life cycle or under certain environmental conditions. A utilization therefore represents an important and widespread mechanism of sensory plasticity. This review provides an up-to-date account of the A/A chromophore exchange system.
脊椎动物的视杆和视锥感光细胞通过一种称为外节的专门细胞器来检测光。这个结构充满了称为视觉色素的光敏感分子，它由一种 G 蛋白偶联的、七次跨膜蛋白组成，称为视蛋白，以及一个发色团辅基，要么是 11-顺式视黄醛（“A”），要么是 11-顺式 3,4-二脱氢视黄醛（“A”）。酶 cyp27c1 将 A 转化为视色素中的 A。在视蛋白中将 A 替换为 A 会使光谱敏感性红移，并扩大其吸收带宽，代价是降低光敏感性和增加热噪声。基于维生素 A 的视觉色素的使用与水生栖息地的占据密切相关，在这些栖息地中，环境光发生红移。通过调节视网膜中的 A/A 比值，生物体可以动态地调整视觉系统的光谱敏感性，以更好地匹配其环境中的主要波长。多达四分之一的脊椎动物物种至少在其生命周期的一部分或在某些环境条件下利用 A。因此，A 的利用代表了一种重要且广泛的感觉可塑性机制。本综述提供了 A/A 发色团交换系统的最新概述。
