During photosynthesis, electrons are transferred between the cytochrome b6f complex and photosystem I. This is carried out by the protein plastocyanin in plant chloroplasts, or by either plastocyanin or cytochrome c6 in many cyanobacteria and eukaryotic algal species. There are three further cytochrome c6 homologs: cytochrome c6A in plants and green algae, and cytochromes c6B and c6C in cyanobacteria. The function of these proteins is unknown. Here, we present a comprehensive analysis of the evolutionary relationship between the members of the cytochrome c6 family in photosynthetic organisms. Our phylogenetic analyses show that cytochromes c6B and c6C are likely to be orthologs that arose from a duplication of cytochrome c6, but that there is no evidence for separate origins for cytochromes c6B and c6C. We therefore propose renaming cytochrome c6C as cytochrome c6B. We show that cytochrome c6A is likely to have arisen from cytochrome c6B rather than by an independent duplication of cytochrome c6, and present evidence for an independent origin of a protein with some of the features of cytochrome c6A in peridinin dinoflagellates. We conclude with a new comprehensive model of the evolution of the cytochrome c6 family which is an integral part of understanding the function of the enigmatic cytochrome c6 homologs.

中文翻译：

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光合电子转移蛋白细胞色素 c6 家族的进化


在光合作用过程中，电子在细胞色素 b6f 复合体和光系统 I 之间转移。这是由植物叶绿体中的质体蓝素蛋白或许多蓝细菌和真核藻类物种中的质体蓝素或细胞色素 c6 进行的。还有另外三种细胞色素 c6 同系物：植物和绿藻中的细胞色素 c6A，以及蓝细菌中的细胞色素 c6B 和 c6C。这些蛋白质的功能尚不清楚。在这里，我们对光合生物中细胞色素c6家族成员之间的进化关系进行了全面分析。我们的系统发育分析表明，细胞色素 c6B 和 c6C 很可能是由细胞色素 c6 重复产生的直系同源物，但没有证据表明细胞色素 c6B 和 c6C 具有不同的起源。因此，我们建议将细胞色素 c6C 重命名为细胞色素 c6B。我们证明细胞色素 c6A 很可能是由细胞色素 c6B 产生的，而不是由细胞色素 c6 的独立复制产生的，并为多甲素甲藻中具有细胞色素 c6A 某些特征的蛋白质的独立起源提供了证据。我们得出了细胞色素 c6 家族进化的新综合模型，这是理解神秘细胞色素 c6 同系物功能的一个组成部分。