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PNAS:华中农大赵开弘课题组发现蓝细菌光合作用机制

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摘要 : 2017年11月27日,国际著名学术期刊《美国科学院院刊》在线发表了华中农业大学生命科学技术学院赵开弘教授课题组与德国杜塞尔多夫大学博士Astrid Höppner、莱比锡大学教授Wolfgang Gärtner和慕尼黑大学教授Hugo Scheer的合作成果
2017年11月27日,国际著名学术期刊《美国科学院院刊》在线发表了华中农业大学生命科学技术学院赵开弘教授课题组与德国杜塞尔多夫大学博士Astrid Höppner、莱比锡大学教授Wolfgang Gärtner和慕尼黑大学教授Hugo Scheer的合作成果,论文题为“Structures and enzymatic mechanisms of phycobiliprotein lyases CpcE/F and PecE/F”。研究报道了蓝细菌光合作用机制,博士研究生赵成为论文第一作者,赵开弘教授为论文通讯作者。 蓝细菌光合作用由藻胆体捕获光能,藻胆体由酶催化形成的色素化藻胆蛋白组成。目前已知有3类不同类型的藻胆蛋白裂合酶:S型、T型和E/F型。在赵开弘课题组发现了S型裂合酶,成功解析了T型裂合酶结构的基础上,本研究通过巧妙设计实验,提纯得到接近天然状态的高纯度CpcE/F蛋白复合物,进一步通过结构生物学解析了CpcE/F蛋白复合物的晶体结构。S型和T型裂合酶只能催化藻胆蛋白共价偶联藻胆色素,E/F型裂合酶除了催化藻胆蛋白共价偶联藻胆色素,还能催化藻胆色素脱离藻胆蛋白、藻胆色素异构化和藻胆蛋白重组与降解等诸多重要过程。因此,E/F型裂合酶在蓝细菌光合作用捕光复合物中发挥着至关重要的作用,但至今为止其结构与作用机制一直是个迷。 根据本研究得到的高分辨率的CpcE/F晶体结构,CpcE/F是一个异源二聚体复合物,整体呈现ɑ-螺线管结构,螺线管环绕形成的内部洞穴负责催化功能。这一工作证明,CpcE/F既能催化藻蓝蛋白共价偶联藻蓝胆素,也能将藻蓝胆素脱离藻蓝蛋白。根据CpcE/F结构模拟得到高同源裂合酶PecE/F蛋白复合物的结构,并通过定点突变发现PecE/F裂合酶的活性中心H87C88,从而证明该活性中心通过藻蓝胆素C10的亲核加成反应驱动藻蓝胆素异构化为藻紫胆素。 据了解,这些结构与机制研究工作为人造光合作用捕光传能元件的设计与创建,为开拓全波段光合作用创造了条件,同时也为通过光合作用捕光传能元件提高农作物光合作用水平奠定了基础。 原文链接: Structures and enzymatic mechanisms of phycobiliprotein lyases CpcE/F and PecE/F 原文摘要: The light-harvesting phycobilisome in cyanobacteria and red algae requires the lyase-catalyzed chromophorylation of phycobiliproteins. There are three functionally distinct lyase families known. The heterodimeric E/F type is specific for attaching bilins covalently to α-subunits of phycocyanins and phycoerythrins. Unlike other lyases, the lyase also has chromophore-detaching activity. A subclass of the E/F-type lyases is, furthermore, capable of chemically modifying the chromophore. Although these enzymes were characterized >25 y ago, their structures remained unknown. We determined the crystal structure of the heterodimer of CpcE/F from Nostoc sp. PCC7120 at 1.89-Å resolution. Both subunits are twisted, crescent-shaped α-solenoid structures. CpcE has 15 and CpcF 10 helices. The inner (concave) layer of CpcE (helices h2, 4, 6, 8, 10, 12, and 14) and the outer (convex) layer of CpcF (h16, 18, 20, 22, and 24) form a cavity into which the phycocyanobilin chromophore can be modeled. This location of the chromophore is supported by mutations at the interface between the subunits and within the cavity. The structure of a structurally related, isomerizing lyase, PecE/F, that converts phycocyanobilin into phycoviolobilin, was modeled using the CpcE/F structure as template. A H87C88 motif critical for the isomerase activity of PecE/F is located at the loop between h20 and h21, supporting the proposal that the nucleophilic addition of Cys-88 to C10 of phycocyanobilin induces the isomerization of phycocyanobilin into phycoviolobilin. Also, the structure of NblB, involved in phycobilisome degradation could be modeled using CpcE as template. Combined with CpcF, NblB shows a low chromophore-detaching activity. doi:10.1073/pnas.1715495114 作者:赵开弘 点击:
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