Department of Chemical Sciences, University of Naples Federico II, Naples, Italy.
Department of Chemical Sciences, University of Naples Federico II, Naples, Italy..
Biochim Biophys Acta Bioenerg. 2020 Sep 1;1861(9):148236. doi: 10.1016/j.bbabio.2020.148236. Epub 2020 May 30.
Galdieria phlegrea is a polyextremophilic red alga belonging to Cyanidiophyceae. Galdieria phlegrea C-phycocyanin (GpPC), an abundant light-harvesting pigment with an important role in energy capture and transfer to photosystems, is the C-phycocyanin (C-PC) with the highest thermal stability described so far. GpPC also presents interesting antioxidant and anticancer activities. The X-ray structure of the protein was here solved. GpPC is a [(αβ)] hexamer, with the phycocyanobilin chromophore attached to Cys84α, Cys82β and Cys153β. Details of geometry and interaction with solvent of the chromophores are reported. Comparison with the structure of a C-PC in the entire Porphyridium purpureum phycobilisome system reveals that linker polypeptides have a significant effect on the local structure of the chromophores environment. Comparative analyses with the structures of other purified C-PCs, which were carried out including re-refined models of G. sulphuraria C-PC, reveal that GpPC presents a significantly higher number of inter-trimer salt bridges. Notably, the higher number of salt bridges at the (αβ)/(αβ) interface is not due to an increased number of charged residues in this region, but to subtle conformational variations of their side chains, which are the result of mutations of close polar and non-polar residues.
胶须藻是一种多极端嗜热红藻，属于蓝藻门。胶须藻藻蓝蛋白（GpPC）是一种丰富的光收集色素，在能量捕获和向光系统转移方面起着重要作用，是迄今为止描述的热稳定性最高的藻蓝蛋白（C-PC）。GpPC 还具有有趣的抗氧化和抗癌活性。本文在此解决了该蛋白的 X 射线结构。GpPC 是一个[(αβ)]六聚体，藻蓝胆素发色团附着在 Cys84α、Cys82β和 Cys153β上。报告了发色团的几何形状和与溶剂相互作用的详细信息。与完整的 Porphyridium purpureum 藻胆体系统中的 C-PC 结构进行比较表明，连接多肽对发色团环境的局部结构有显著影响。与其他纯化的 C-PC 结构的比较分析，包括重新精修的 G. sulphuraria C-PC 模型，表明 GpPC 呈现出更高数量的三聚体盐桥。值得注意的是，（αβ）/（αβ）界面处盐桥数量的增加并不是由于该区域带电荷残基数量的增加，而是由于其侧链的细微构象变化，这是由于附近极性和非极性残基的突变所致。
