Schmid V H, Cammarata K V, Bruns B U, Schmidt G W
Department of Botany, University of Georgia, Athens, GA 30602-7271, USA.
Proc Natl Acad Sci U S A. 1997 Jul 8;94(14):7667-72. doi: 10.1073/pnas.94.14.7667.
Here we describe the in vitro reconstitution of photosystem I light-harvesting complexes with pigments and proteins (Lhca1 and Lhca4) obtained by overexpression of tomato Lhca genes in Escherichia coli. Using Lhca1 and Lhca4 individually for reconstitution results in monomeric pigment-proteins, whereas a combination thereof yields a dimeric complex. Interactions of the apoproteins is highly specific, as reconstitution of either of the two constituent proteins in combination with a light-harvesting protein of photosystem II does not result in dimerization. The reconstituted Lhca1/4, but not complexes obtained with either Lhca1 or Lhca4 alone, closely resembles the native LHCI-730 dimer from tomato leaves with regard to spectroscopic properties, pigment composition, and stoichiometry. Monomeric complexes of Lhca1 or Lhca4 possess lower pigment/protein ratios, indicating that interactions of the two subunits not only facilitates pigment reorganization but also recruitment of additional pigments. In addition to higher averages of chlorophyll a/b ratios in monomeric complexes than in LHCI-730, comparative fluorescence and CD spectra demonstrate that heterodimerization involves preferential ligation of more chlorophyll b.
在此，我们描述了通过在大肠杆菌中过表达番茄Lhca基因获得的色素和蛋白质（Lhca1和Lhca4）对光系统I捕光复合体进行的体外重建。单独使用Lhca1和Lhca4进行重建会产生单体色素 - 蛋白质，而将它们组合使用则会产生二聚体复合物。脱辅基蛋白的相互作用具有高度特异性，因为两种组成蛋白中的任何一种与光系统II的捕光蛋白组合重建都不会导致二聚化。重建的Lhca1/4，而不是单独使用Lhca1或Lhca4获得的复合物，在光谱性质、色素组成和化学计量方面与来自番茄叶片的天然LHCI - 730二聚体非常相似。Lhca1或Lhca4的单体复合物具有较低的色素/蛋白质比率，这表明两个亚基的相互作用不仅促进色素重组，还促进额外色素的募集。除了单体复合物中的叶绿素a/b比率平均值高于LHCI - 730之外，比较荧光和圆二色光谱表明，异源二聚化涉及更多叶绿素b的优先连接。
