Passarini Francesca, Wientjes Emilie, van Amerongen Herbert, Croce Roberta
Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
Biochim Biophys Acta. 2010 Apr;1797(4):501-8. doi: 10.1016/j.bbabio.2010.01.015. Epub 2010 Jan 25.
In this work we have investigated the origin of the multi-exponential fluorescence decay and of the short excited-state lifetime of Lhca4. Lhca4 is the antenna complex of Photosystem I which accommodates the red-most chlorophyll forms and it has been proposed that these chlorophylls can play a role in fluorescence quenching. Here we have compared the fluorescence decay of Lhca4 with that of several Lhca4 mutants that are affected in their red form content. The results show that neither the multi-exponentiality of the decay nor the fluorescence quenching is due to the red forms. The data indicate that Lhca4 exists in multiple conformations. The presence of the red forms, which are very sensitive to changes in the environment, allows to spectrally resolve the different conformations: a "blue" conformation with a short lifetime and a "red" one with a long lifetime. This finding strongly supports the idea that the members of the Lhc family are able to adopt different conformations associated with their light-harvesting and photoprotective roles. The ratio between the conformations is modified by the substitution of lutein by violaxanthin. Finally, it is demonstrated that the red forms cannot be present in the quenched conformation.
在这项工作中，我们研究了Lhca4多指数荧光衰减的起源以及其短激发态寿命的起源。Lhca4是光系统I的天线复合体，容纳最红的叶绿素形式，并且有人提出这些叶绿素可能在荧光猝灭中起作用。在这里，我们将Lhca4的荧光衰减与几种红色形式含量受影响的Lhca4突变体的荧光衰减进行了比较。结果表明，衰减的多指数性和荧光猝灭都不是由红色形式引起的。数据表明Lhca4以多种构象存在。对环境变化非常敏感的红色形式的存在，使得能够在光谱上分辨出不同的构象：一种寿命短的“蓝色”构象和一种寿命长的“红色”构象。这一发现有力地支持了这样一种观点，即Lhc家族的成员能够采用与其光捕获和光保护作用相关的不同构象。通过用紫黄质取代叶黄素，构象之间的比例发生了改变。最后，证明了红色形式不能以猝灭构象存在。
