van Thor J J, Gruters O W, Matthijs H C, Hellingwerf K J
E.C.Slater Institute, Department of Microbiology, 1018 WS Amsterdam, The Netherlands.
EMBO J. 1999 Aug 2;18(15):4128-36. doi: 10.1093/emboj/18.15.4128.
Each phycobilisome complex of the cyanobacterium Synechocystis PCC 6803 binds approximately 2.4 copies of ferredoxin:NADP(+) reductase (FNR). A mutant of this strain that carries an N-terminally truncated version of the petH gene, lacking the 9 kDa domain of FNR that is homologous to the phycocyanin-associated linker polypeptide CpcD, assembles phycobilisome complexes that do not contain FNR. Phycobilisome complexes, consisting of the allophycocyanin core and only the core-proximal phycocyanin hexamers from mutant R20, do contain a full complement of FNR. Therefore, the binding site of FNR in the phycobilisomes is not the core-distal binding site that is occupied by CpcD, but in the core-proximal phycocyanin hexamer. Phycobilisome complexes of a mutant expressing a fusion protein of the N-terminal domain of FNR and green fluorescent protein (GFP) contain this fusion protein in tightly bound form. Calculations of the fluorescence resonance energy transfer (FRET) characteristics between GFP and acceptors in the phycobilisome complex indicate that their donor-acceptor distance is between 3 and 7 nm. Fluorescence spectroscopy at 77K and measurements in intact cells of accumulated levels of P700(+) indicate that the presence of FNR in the phycobilisome complexes does not influence the distribution of excitation energy of phycobilisome-absorbed light between photosystem II and photosystem I, and also does not affect the occurrence of 'light-state transitions'.
集胞藻PCC 6803的每个藻胆体复合物结合约2.4个铁氧还蛋白：NADP(+)还原酶（FNR）拷贝。该菌株的一个突变体携带petH基因的N端截短版本，缺少与藻蓝蛋白相关连接多肽CpcD同源的FNR的9 kDa结构域，其组装的藻胆体复合物不含FNR。由别藻蓝蛋白核心和仅来自突变体R20的核心近端藻蓝蛋白六聚体组成的藻胆体复合物确实含有完整的FNR。因此，藻胆体中FNR的结合位点不是被CpcD占据的核心远端结合位点，而是在核心近端藻蓝蛋白六聚体中。表达FNR N端结构域与绿色荧光蛋白（GFP）融合蛋白的突变体的藻胆体复合物以紧密结合形式包含这种融合蛋白。藻胆体复合物中GFP与受体之间荧光共振能量转移（FRET）特性的计算表明，它们的供体-受体距离在3至7 nm之间。77K下的荧光光谱以及完整细胞中P700(+)积累水平的测量表明，藻胆体复合物中FNR的存在不影响藻胆体吸收光的激发能在光系统II和光系统I之间的分布，也不影响“光状态转换”的发生。
