Phycobilisomes are light-harvesting antenna complexes of cyanobacteria and red algae that are comprised of chromoproteins called phycobiliproteins. PBS core structures are made up of allophycocyanin subunits. Halomicronema hongdechloris (H. hongdechloris) is one of the cyanobacteria that produce chlorophyll f (Chl f) under far-red light and is regulated by the Far-Red Light Photoacclimation gene cluster. There are five genes encoding APC in this specific gene cluster, and they are responsible for assembling the red-shifted PBS in H. hongdechloris grown under far-red light. In this study, the five apc genes located in the FaRLiP gene cluster were heterologously expressed in an Escherichia coli reconstitution system. The canonical APC-encoding genes were also constructed in the same system for comparison. Additionally, five annotated phycobiliprotein lyase-encoding genes (cpcS) from the H. hongdechloris genome were phylogenetically classified and experimentally tested for their catalytic properties including their contribution to the shifted absorption of PBS. Through analysis of recombinant proteins, we determined that the heterodimer of CpcS-I and CpcU are able to ligate a chromophore to the APC-α/APC-β subunits. We discuss some hypotheses towards understanding the roles of the specialised APC and contributions of PBP lyases.

藻胆体是蓝藻和红藻的捕光天线复合物，由称为藻胆蛋白的色素蛋白组成。PBS 核心结构由别藻蓝蛋白亚基组成。Halomicronema hongdechloris ( H. hongdechloris ) 是在远红光下产生叶绿素f (Chl f ) 的蓝细菌之一，受远红光光驯化基因簇的调控。在这个特定的基因簇中有五个编码 APC 的基因，它们负责在远红光下生长的H. hongdechloris中组装红移的 PBS 。在这项研究中，位于 FaRLiP 基因簇中的五个apc基因在一个大肠杆菌重组系统。规范的 APC 编码基因也在同一系统中构建以进行比较。此外，对来自H. hongdechloris基因组的五个带注释的藻胆蛋白裂解酶编码基因 ( cpcS ) 进行了系统发育分类，并对其催化特性进行了实验测试，包括它们对 PBS 转移吸收的贡献。通过对重组蛋白的分析，我们确定 CpcS-I 和 CpcU 的异二聚体能够将发色团连接到 APC-α/APC-β 亚基上。我们讨论了一些假设，以了解专门 APC 的作用和 PBP 裂解酶的贡献。