Juhas Matthias, von Zadow Andrea, Spexard Meike, Schmidt Matthias, Kottke Tilman, Büchel Claudia
Institute of Molecular Biosciences, University of Frankfurt, Germany.
FEBS J. 2014 May;281(9):2299-311. doi: 10.1111/febs.12782. Epub 2014 Apr 7.
Diatoms possess several genes for proteins of the cryptochrome/photolyase family. A typical sequence for a plant cryptochrome was not found in our analysis of the Phaeodactylum tricornutum genome, but one protein grouped with higher plant and green algal cryptochromes. This protein, CryP, binds FAD and 5,10-methenyltetrahydrofolate, according to our spectroscopic studies on heterologously expressed protein. 5,10-Methenyltetrahydrofolate binding is a feature common to both cyclobutane pyrimidine dimer photolyases and DASH cryptochromes. In recombinant CryP, however, the FAD chromophore was present in its neutral radical state and had a red-shifted absorption maximum at 637 nm, which is more characteristic for a DASH cryptochrome than a cyclobutane pyrimidine dimer photolyase. Upon illumination with blue light, the fully reduced state of FAD was formed in the presence of reductant. Expression of CryP was silenced by antisense approaches, and the resulting cell lines showed increased levels of proteins of light-harvesting complexes, the Lhcf proteins, in vivo. In contrast, the levels of proteins active in light protection, the Lhcx proteins, were reduced. Thus, CryP cannot be directly grouped with known members of the cryptochrome/photolyase family. Of all P. tricornutum proteins, it is the most similar in sequence to a plant cryptochrome, and is involved in the regulation of light-harvesting protein expression, but shows spectroscopic features and a chromophore composition that are most typical of a DASH cryptochrome.
硅藻拥有几个编码隐花色素/光解酶家族蛋白质的基因。在我们对三角褐指藻基因组的分析中未发现植物隐花色素的典型序列，但有一种蛋白质与高等植物和绿藻的隐花色素归为一类。根据我们对异源表达蛋白的光谱研究，这种名为CryP的蛋白质结合FAD和5,10-亚甲基四氢叶酸。5,10-亚甲基四氢叶酸结合是环丁烷嘧啶二聚体光解酶和DASH隐花色素共有的特征。然而，在重组CryP中，FAD发色团以其中性自由基状态存在，在637nm处有一个红移的最大吸收峰，这对于DASH隐花色素来说比环丁烷嘧啶二聚体光解酶更具特征性。在蓝光照射下，在有还原剂存在的情况下会形成FAD的完全还原态。通过反义方法使CryP的表达沉默，所得细胞系在体内显示出捕光复合物蛋白（Lhcf蛋白）水平升高。相反，在光保护中起作用的蛋白（Lhcx蛋白）水平降低。因此，CryP不能直接与隐花色素/光解酶家族的已知成员归为一类。在所有三角褐指藻蛋白中，它在序列上与植物隐花色素最相似，并且参与捕光蛋白表达的调节，但显示出DASH隐花色素最典型的光谱特征和发色团组成。
