PNAS:华中农业大学赵开弘课题组发表光合作用捕光传能过程研究

光合作用利用太阳能将无机物转化为生物可利用的有机物，是自然界最重要的生物化学反应。蓝细菌是光合作用研究的良好模型。蓝细菌捕光色素复合物为藻胆体，核膜连接蛋白LCM是藻胆体中一个多结构域多功能的蛋白，参与藻胆体核心复合物的形成，将藻胆体锚定于类囊体膜上，还能将能量从藻胆体传递到光合反应中心。

赵开弘课题组本次研究的创新之处在于首次解析了蓝细菌藻胆体核膜连接蛋白N端色素结构域的晶体结构，发现其拥有不同于其他藻胆蛋白的色素结构ZZZssa，并结合瞬态光谱分析了其特征光谱红移的原因，及其能量传递的机制。这将为进一步研究蓝细菌光合作用的捕光传能，利用其结构与光谱特征人工设计光合作用器件奠定了基础。

原文链接：

The terminal phycobilisome emitter, LCM: A light-harvesting pigment with a phytochrome chromophore

原文摘要：

Photosynthesis relies on energy transfer from light-harvesting complexes to reaction centers. Phycobilisomes, the light-harvesting antennas in cyanobacteria and red algae, attach to the membrane via the multidomain core-membrane linker, LCM. The chromophore domain of LCM forms a bottleneck for funneling the harvested energy either productively to reaction centers or, in case of light overload, to quenchers like orange carotenoid protein (OCP) that prevent photodamage. The crystal structure of the solubly modified chromophore domain from Nostoc sp. PCC7120 was resolved at 2.2 Å. Although its protein fold is similar to the protein folds of phycobiliproteins, the phycocyanobilin (PCB) chromophore adoptsZZZssa geometry, which is unknown among phycobiliproteins but characteristic for sensory photoreceptors (phytochromes and cyanobacteriochromes). However, chromophore photoisomerization is inhibited in LCMby tight packing. The ZZZssa geometry of the chromophore and π-π stacking with a neighboring Trp account for the functionally relevant extreme spectral red shift of LCM. Exciton coupling is excluded by the large distance between two PCBs in a homodimer and by preservation of the spectral features in monomers. The structure also indicates a distinct flexibility that could be involved in quenching. The conclusions from the crystal structure are supported by femtosecond transient absorption spectra in solution.

doi: 10.1073/pnas.1519177113

作者：赵开弘