Institute for Integrative Biology of the Cell, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Université Paris-Sud, Université Paris-Saclay, 91198 Gif sur Yvette, France.
Institut de Biologie et Technologies de Saclay, Commissariat à l'Energie Atomique, 91191 Gif-sur-Yvette, France.
Plant Physiol. 2017 Nov;175(3):1283-1303. doi: 10.1104/pp.17.01040. Epub 2017 Sep 21.
The photoactive Orange Carotenoid Protein (OCP) photoprotects cyanobacteria cells by quenching singlet oxygen and excess excitation energy. Its N-terminal domain is the active part of the protein, and the C-terminal domain regulates the activity. Recently, the characteristics of a family of soluble carotenoid-binding proteins (Helical Carotenoid Proteins [HCPs]), paralogs of the N-terminal domain of OCP, were described. Bioinformatics studies also revealed the existence of genes coding for homologs of CTD. Here, we show that the latter genes encode carotenoid proteins (CTDHs). This family of proteins contains two subgroups with distinct characteristics. One CTDH of each clade was further characterized, and they proved to be very good singlet oxygen quenchers. When synthesized in or PCC 6803, CTDHs formed dimers that share a carotenoid molecule and are able to transfer their carotenoid to apo-HCPs and apo-OCP. The CTDHs from clade 2 have a cysteine in position 103. A disulfide bond is easily formed between the monomers of the dimer preventing carotenoid transfer. This suggests that the transfer of the carotenoid could be redox regulated in clade 2 CTDH. We also demonstrate here that apo-OCPs and apo-CTDHs are able to take the carotenoid directly from membranes, while HCPs are unable to do so. HCPs need the presence of CTDH to become holo-proteins. We propose that, in cyanobacteria, the CTDHs are carotenoid donors to HCPs.
光激活的橙色类胡萝卜素蛋白 (OCP) 通过猝灭单线态氧和过量激发能来保护蓝细菌细胞。其 N 端结构域是该蛋白的活性部分,而 C 端结构域调节其活性。最近,描述了一类可溶性类胡萝卜素结合蛋白(螺旋类胡萝卜素蛋白 [HCP])的特性,它们是 OCP N 端结构域的旁系同源物。生物信息学研究还揭示了编码 CTD 同源物基因的存在。在这里,我们表明,后一类基因编码类胡萝卜素蛋白(CTDHs)。该蛋白家族包含两个具有不同特征的亚群。每个分支的一个 CTDH 进一步被表征,它们被证明是非常好的单线态氧猝灭剂。当在 或 PCC 6803 中合成时,CTDHs 形成二聚体,共享一个类胡萝卜素分子,并能够将其类胡萝卜素转移给 apo-HCPs 和 apo-OCP。来自 2 分支的 CTDHs 在位置 103 有一个半胱氨酸。二聚体单体之间很容易形成二硫键,从而阻止类胡萝卜素的转移。这表明在 2 分支的 CTDH 中,类胡萝卜素的转移可以被氧化还原调节。我们还在这里证明,apo-OCPs 和 apo-CTDHs 能够直接从膜中获取类胡萝卜素,而 HCPs 则不能。HCPs 需要 CTDH 的存在才能成为全蛋白。我们提出,在蓝细菌中,CTDHs 是 HCPs 的类胡萝卜素供体。