Federal Research Center of Biotechnology of the Russian Academy of Sciences, A.N. Bach Institute of Biochemistry, Moscow, Russia.
Department of Biochemistry, Faculty of Biology, M.V. Lomonosov Moscow State University, Russia.
FEBS J. 2019 May;286(10):1908-1924. doi: 10.1111/febs.14803. Epub 2019 Mar 22.
Carotenoids are lipophilic pigments with multiple biological functions from coloration to vision and photoprotection. Still, the number of water-soluble carotenoid-binding proteins described to date is limited, and carotenoid transport and carotenoprotein maturation processes are largely underexplored. Recent studies revealed that CTDHs, which are natural homologs of the C-terminal domain (CTD) of the orange carotenoid protein (OCP), a photoswitch involved in cyanobacterial photoprotection, are able to bind carotenoids, with absorption shifted far into the red region of the spectrum. Despite the recent discovery of their participation in carotenoid transfer processes, the functional roles of the diverse family of CTDHs are not well understood. Here, we characterized CTDH carotenoproteins from Anabaena variabilis (AnaCTDH) and Thermosynechococcus elongatus and examined their ability to participate in carotenoid transfer processes with a set of OCP-derived proteins. This revealed that carotenoid transfer occurs in several directions guided by different affinities for carotenoid and specific protein-protein interactions. We show that CTDHs have higher carotenoid affinity compared to the CTD of OCP from Synechocystis, which results in carotenoid translocation from the CTD into CTDH via a metastable heterodimer intermediate. Activation of OCP by light, or mutagenesis compromising the OCP structure, provides AnaCTDH with an opportunity to extract carotenoid from the full-length OCP, either from Synechocystis or Anabaena. These previously unknown reactions between water-soluble carotenoproteins demonstrate multidirectionality of carotenoid transfer, allowing for efficient and reversible control over the carotenoid-mediated protein oligomerization by light, which gives insights into the physiological regulation of OCP activity by CTDH and suggests multiple applications.
类胡萝卜素是具有多种生物学功能的亲脂性色素，从着色到视觉和光保护。尽管迄今为止描述的水溶性类胡萝卜素结合蛋白的数量有限，但类胡萝卜素的转运和类胡萝卜蛋白成熟过程在很大程度上仍未得到探索。最近的研究表明，CTDHs 是橙色类胡萝卜素蛋白（OCP）C 端结构域（CTD）的天然同源物，OCP 是一种参与蓝细菌光保护的光开关，能够结合类胡萝卜素，吸收峰远移到光谱的红区。尽管最近发现它们参与了类胡萝卜素转移过程，但 CTDH 家族的各种功能作用仍未得到很好的理解。在这里，我们对来自可变鱼腥藻（AnaCTDH）和 elongatus Thermosynechococcus 的 CTDH 类胡萝卜蛋白进行了表征，并研究了它们与一组 OCP 衍生蛋白参与类胡萝卜素转移过程的能力。这表明，在不同的类胡萝卜素和特定的蛋白质-蛋白质相互作用亲和力的指导下，类胡萝卜素的转移发生在几个方向上。我们表明，与来自集胞藻的 OCP 的 CTD 相比，CTDH 具有更高的类胡萝卜素亲和力，这导致类胡萝卜素通过亚稳态异源二聚体中间体从 CTD 转移到 CTDH。光对 OCP 的激活，或破坏 OCP 结构的突变，为 AnaCTDH 提供了从全长 OCP 中提取类胡萝卜素的机会，无论是来自集胞藻还是鱼腥藻。这些以前未知的水溶性类胡萝卜蛋白之间的反应表明类胡萝卜素转移的多方向性，允许通过光对类胡萝卜素介导的蛋白质寡聚化进行有效和可逆的控制，这为 OCP 活性由 CTDH 进行生理调节提供了深入的了解，并暗示了多种应用。
