Phycobilisomes are large light-harvesting complexes attached to the stromal side of thylakoids in cyanobacteria and red algae. They can be remodeled or degraded in response to changing light and nutritional status. Both the core and the peripheral rods of phycobilisomes contain biliproteins. During biliprotein biosynthesis, open-chain tetrapyrrole chromophores are attached covalently to the apoproteins by dedicated lyases. Another set of non-bleaching (Nb) proteins has been implicated in phycobilisome degradation, among them NblA and NblB. We report in vitro experiments with lyases, biliproteins and NblA/B which imply that the situation is more complex than currently discussed: lyases can also detach the chromophores and NblA and NblB can modulate lyase-catalyzed binding and detachment of chromophores in a complex fashion. We show: (i) NblA and NblB can interfere with chromophorylation as well as chromophore detachment of phycobiliprotein, they are generally inhibitors but in some cases enhance the reaction; (ii) NblA and NblB promote dissociation of whole phycobilisomes, cores and, in particular, allophycocyanin trimers; (iii) while NblA and NblB do not interact with each other, both interact with lyases, apo- and holo-biliproteins; (iv) they promote synergistically the lyase-catalyzed chromophorylation of the β-subunit of the major rod component, CPC; and (v) they modulate lyase-catalyzed and lyase-independent chromophore transfers among biliproteins, with the core protein, ApcF, the rod protein, CpcA, and sensory biliproteins (phytochromes, cyanobacteriochromes) acting as potential traps. The results indicate that NblA/B can cooperate with lyases in remodeling the phycobilisomes to balance the metabolic requirements of acclimating their light-harvesting capacity without straining the overall metabolic economy of the cell.

中文翻译：

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裂解酶，NblA和NblB蛋白以及Bilin生色团转移在重组蓝细菌光捕获复合物中的作用‡。

藻胆体是附着在蓝藻和红藻类囊体的基质侧的大型集光复合体。它们可以根据光照和营养状况的变化而重塑或降解。藻胆体的核心杆和外围杆均含有胆蛋白。在胆蛋白的生物合成过程中，开链的四吡咯发色团通过专用的裂解酶共价附于载脂蛋白。另一组非漂白（Nb）蛋白与藻胆体降解有关，其中包括NblA和NblB。我们报告了裂解酶，胆汁蛋白和NblA / B的体外实验，这表明情况比当前讨论的情况更为复杂：裂解酶还可以使发色团脱离，而NblA和NblB可以以复杂的方式调节裂解酶催化的发色团结合和脱离。我们显示：（i）NblA和NblB会干扰藻胆蛋白的发色以及发色团的分离，它们通常是抑制剂，但在某些情况下会增强反应；（ii）NblA和NblB促进整个藻胆体，核心，特别是别花青素三聚体的解离；（iii）虽然NblA和NblB不相互作用，但都与裂解酶，脱辅基和全胆蛋白相互作用。（iv）它们协同促进主要杆组分CPC的β-亚基的裂解酶催化的发色作用；（v）他们调节胆汁蛋白之间裂解酶催化和不依赖裂解酶的生色团转移，核心蛋白ApcF，棒蛋白，CpcA和感觉胆汁蛋白（植物色素，蓝细菌色素）起着潜在的陷阱的作用。