Phycobiliproteins (PBPs) are pigment proteins that comprise phycobilisomes (PBS), major light-harvesting antenna complexes of cyanobacteria and red algae. PBS core substructures are made up of allophycocyanins (APs), a subfamily of PBPs. Five paralogous AP subunits are encoded by the Far-Red Light Photoacclimation (FaRLiP) gene cluster, which is transcriptionally activated in cells grown in far-red light (FRL; λ = 700 to 800 nm). FaRLiP gene expression enables some terrestrial cyanobacteria to remodel their PBS and photosystems and perform oxygenic photosynthesis in far-red light (FRL). Paralogous AP genes encoding a putative, FRL-absorbing AP (FRL-AP) are also found in an operon associated with improved low-light growth (LL; < 50 μmol photons m^–2 s^–1) in some thermophilic Synechococcus spp., a phenomenon termed low-light photoacclimation (LoLiP). In this study, apc genes from FaRLiP and LoLiP gene clusters were heterologously expressed individually and in combinations in Escherichia coli. The resulting novel FRL-APs were characterized and identified as major contributors to the FRL absorbance observed in whole cells after FaRLiP and potentially LoLiP. Post-translational modifications of native FRL-APs from FaRLiP cyanobacterium, Leptolyngbya sp. strain JSC-1, were analyzed by mass spectrometry. The PBP complexes made in two FaRLiP organisms were compared, revealing strain-specific diversity in the FaRLiP responses of cyanobacteria. Through analyses of native and recombinant proteins, we improved our understanding of how different cyanobacterial strains utilize specialized APs to acclimate to FRL and LL. We discuss some insights into structural changes that may allow these APs to absorb longer light wavelengths than their visible-light-absorbing paralogs.

藻胆蛋白（PBPs）是色素蛋白，包含藻胆体（PBS），蓝细菌和红藻的主要捕光触角复合物。PBS核心亚结构由别藻蓝蛋白（APs）（PBP的一个子家族）组成。五个旁源AP亚基由远红光光适应（FaRLiP）基因簇编码，该簇在远红光（FRL; λ  = 700至800 nm）中生长的细胞中被转录激活。FaRLiP基因表达使一些陆地蓝细菌能够重塑其PBS和光系统，并在远红光（FRL）中进行含氧光合作用。在操纵子中还发现了编码假定的吸收FRL的AP（FRL-AP）的旁系AP基因，与弱光生长改善有关（LL； <50μmol光子m ^–2  s ^–1）在一些嗜热聚球藻属物种，这种现象被称为低光photoacclimation（LoLiP）。在这项研究中，来自FaRLiP和LoLiP基因簇的apc基因在大肠杆菌中单独或组合异源表达。表征并鉴定了所得的新型FRL-APs是导致FaRLiP和潜在的LoLiP在整个细胞中观察到的FRL吸收的主要因素。FaRLiP蓝细菌，钩端螺旋体中天然FRL-AP的翻译后修饰sp。通过质谱分析菌株JSC-1。比较了在两种FaRLiP生物体中制成的PBP复合物，揭示了蓝细菌FaRLiP反应中的菌株特异性多样性。通过对天然和重组蛋白的分析，我们进一步了解了不同的蓝细菌菌株如何利用专门的AP适应FRL和LL。我们讨论了有关结构变化的一些见解，这些变化可能使这些AP吸收比吸收可见光的对位物更长的光波长。