Analysis of the assembly apparatus of photosystem I reaction center complex

叶绿体编码的YCF4是一种类囊体蛋白，对光系统I(PSI)反应中心复合体的组装是必不可少的。这个蛋白质是一个大的复合体的一部分，它是PSI复合体的组装装置。本研究采用两步亲和层析法，从表达YCF4与TAP-Tag融合的莱茵衣藻叶绿体转化子的类囊体液中分离纯化了YCF4-复合体。结果发现，YCF4-复合体含有视网膜结合蛋白Cop2和MASAP(线粒体ATP合成酶相关蛋白)，以及PSI亚基之一的PSAF和YCF4。单独的生化实验发现，类囊体中存在的所有Cop2都与Ycf4共纯化，表明这种视网膜结合蛋白是Ycf4-复合体的真实成分。目前尚不清楚Cop2的功能。吸收光谱和荧光发射光谱表明，纯化的YCF4-络合物含有叶绿素和类胡萝卜素。这些颜料可以提供给PSI络合物的组装中间体。

Chloroplast-encoded Ycf4 is a thylakoidal protein and is essential for the assembly of photosystem I (PSI) reaction center complex. This protein is a part of a large complex that is an assembly apparatus of PSI complex. In this project, the Ycf4-complex was highly purified by two steps affinity chromatography from the thylakoid extracts of the chloroplast transformant of Chlamydomonas reinhardtii in which Ycf4 fused with TAP-tag is expressed. The resultant Ycf4-complex was found to contain Cop2, the retinal binding protein, and MASAP (mitochondrial ATP synthase associated protein) as well as PsaF, one of the PSI subunits and Ycf4. It was found from separate biochemical experiments that all Cop2 present in the thylakoids is co-purified with Ycf4, indicating that this retinal binding protein is an authentic component of the Ycf4-complex. The functional role of Cop2 is not yet known. Absorption and fluorescence emission spectra revealed that the purified Ycf4-complex contains chlorophyll and carotenoid. These pigments may be supplied to an assembly intermediate of PSI complex.