Structure of a photosystem II supercomplex isolated from Prochlorion didemni retaining its chlorophyll a/b light-harvesting system
Structure of a photosystem II supercomplex isolated from Prochlorion didemni retaining its chlorophyll a/b light-harvesting system
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DOI：
10.1073/pnas.1532271100
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发表时间：
2003-07-22
影响因子：
11.1
通讯作者：
Barber, J
中科院分区：
文献类型：
--
作者：
Bibby, TS;Nield, J;Barber, J
原绿藻是一类蓝藻，不使用藻胆蛋白作为捕光系统，但含有叶绿素(Chl)a/b结合的印刷电路板蛋白。最近的研究表明，在原绿藻原氯球菌SS120的光系统I(PSI)三聚体反应中心复合体周围，PCB蛋白形成了一个18个亚基的捕光天线环。在这里，我们研究了共生的原绿藻类原绿藻是否也含有相同的超分子复合体。使用直接从其腹水宿主分离的细胞，我们没有发现PCBPSI超复合体存在的证据。相反，我们已经鉴定并鉴定了一个由光系统II(PSII)和多氯联苯蛋白质组成的超复合体。我们发现10-PCB亚单位与PSII二聚体反应中心核心结合形成一个巨大的复合体，其M-r估计为1500 kDa，尺寸为210×290埃。五个PCB亚单位位于二聚体每一长边的侧翼，假设每个亚单位结合13个Chl分子，则PSR的天线尺寸增加约200%。荧光发射研究表明，能量从印刷电路板天线有效地传递。利用蓝藻PSII的X射线结构建模表明，能量通过与CP47和CP43蛋白结合的CHL传递到PSII反应中心。
Prochlorophytes are a class of cyanobacteria that do not use phycobiliproteins as light-harvesting systems, but contain chlorophyll (Chl) a/b-binding Pcb proteins. Recently it was shown that Pcb proteins form an 18-subunit light-harvesting antenna ring around the photosystem I (PSI) trimeric reaction center complex of the prochlorophyte Prochlorococcus marinus SS120. Here we have investigated whether the symbiotic prochlorophyte Prochloron didemni also contains the same supermolecular complex. Using cells isolated directly from its ascidian host, we found no evidence for the presence of the Pcb-PSI supercomplex. Instead we have identified and characterized a supercomplex composed of photosystem II (PSII) and Pcb proteins. We show that 10-Pcb subunits associate with the PSII dimeric reaction center core to form a giant complex having an estimated M-r of 1,500 kDa with dimensions of 210 x 290 Angstrom. Five-Pcb subunits flank each long side of the dimer and assuming each binds 13 Chl molecules, increase the antenna size of PSR by approximate to200%. Fluorescence emission studies indicate that energy transfer occurs efficiently from the Pcb antenna. Modeling using the x-ray structure of cyanobacterial PSII suggests that energy transfer to the PSII reaction center is via the Chls bound to the CP47 and CP43 proteins.