Radzin Szymon, Wiśniewska-Becker Anna, Markiewicz Michał, Bętkowski Sebastian, Furso Justyna, Waresiak Joanna, Grolik Jarosław, Sarna Tadeusz, Pawlak Anna M
Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Krakow, Poland.
Department of Computational Biophysics and Bioinformatics, Faculty of Biochemistry, Biophysics, Jagiellonian University, 30-387 Krakow, Poland.
Membranes (Basel). 2023 Jun 1;13(6):575. doi: 10.3390/membranes13060575.
Photoreceptor membranes have a unique lipid composition. They contain a high level of polyunsaturated fatty acids including the most unsaturated fatty acid in nature, docosahexaenoic acid (22:6), and are enriched in phosphatidylethanolamines. The phospholipid composition and cholesterol content of the subcellular components of photoreceptor outer segments enables to divide photoreceptor membranes into three types: plasma membranes, young disc membranes, and old disc membranes. A high degree of lipid unsaturation, extended exposure to intensive irradiation, and high respiratory demands make these membranes sensitive to oxidative stress and lipid peroxidation. Moreover, all-trans retinal (AtRAL), which is a photoreactive product of visual pigment bleaching, accumulates transiently inside these membranes, where its concentration may reach a phototoxic level. An elevated concentration of AtRAL leads to accelerated formation and accumulation of bisretinoid condensation products such as A2E or AtRAL dimers. However, a possible structural impact of these retinoids on the photoreceptor-membrane properties has not yet been studied. In this work we focused just on this aspect. The changes induced by retinoids, although noticeable, seem not to be significant enough to be physiologically relevant. This is, however, an positive conclusion because it can be assumed that accumulation of AtRAL in photoreceptor membranes will not affect the transduction of visual signals and will not disturb the interaction of proteins engaged in this process.
光感受器膜具有独特的脂质组成。它们含有高水平的多不饱和脂肪酸，包括自然界中最不饱和的脂肪酸二十二碳六烯酸（22:6），并且富含磷脂酰乙醇胺。光感受器外段亚细胞成分的磷脂组成和胆固醇含量使得光感受器膜能够分为三种类型：质膜、年轻盘膜和老化盘膜。高度的脂质不饱和、长时间暴露于强辐射以及高呼吸需求使得这些膜对氧化应激和脂质过氧化敏感。此外，全反式视黄醛（AtRAL）是视觉色素漂白的光反应产物，会在这些膜内短暂积累，其浓度可能达到光毒性水平。AtRAL浓度升高会导致双视黄醛缩合产物如A2E或AtRAL二聚体的加速形成和积累。然而，这些类视黄醇对光感受器膜特性可能的结构影响尚未得到研究。在这项工作中，我们恰恰关注这一方面。类视黄醇诱导的变化虽然明显，但似乎在生理相关性上还不够显著。然而，这是一个积极的结论，因为可以假定AtRAL在光感受器膜中的积累不会影响视觉信号的转导，也不会干扰参与这一过程的蛋白质之间的相互作用。
