Characterization of the photoactive GAF domain of the CikA homolog (SyCikA, Slr1969) of the cyanobacterium Synechocystis sp PCC 6803
Characterization of the photoactive GAF domain of the CikA homolog (SyCikA, Slr1969) of the cyanobacterium Synechocystis sp PCC 6803
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DOI：
10.1039/b811214b
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发表时间：
2008-10-01
影响因子：
3.1
通讯作者：
Ikeuchi, Masahiko
中科院分区：
文献类型：
--
作者：
Narikawa, Rei;Kohchi, Takayuki;Ikeuchi, Masahiko
植物中的光敏色素和细菌色光色素分别是结合线性四吡咯的光感受器，可以以可逆的方式响应红光和远红光信号。据报道，一种相关但不同的光感受器候选物质CikA（标记为ScCikA）可以在暗脉冲后重置蓝藻长聚球菌PCC 7942的生物钟。然而，最近的研究表明，ScCikA不是光感受器，而是氧化还原传感器。此外，光敏色素中共价连接发色团的Cys残基在ScCikA蛋白中并不保守。另一方面，Synechocystis sp. PCC 6803 （Sir 1969，记作SyCikA）中的CikA同源物保留了这个保守的Cys残基。在我们目前的研究中，我们从聚胞菌和产藻蓝胆素的大肠杆菌中分离出了SyCikA的推测的发色团结合GAF结构域。两种制剂的吸收光谱均在紫外区和紫外区出现两个峰。用紫光照射这些蛋白质，在黄色区域产生一个宽峰，而牺牲了紫外和紫色区域的峰。有趣的是，连续的黄光照射并没有恢复这些吸收光谱，但检测到部分暗还原到原始形式。这些结果表明SyCikA可能在聚囊藻中起紫光传感器的作用。
Phytochromes and bacteriophytochromes in plants and some species of bacteria, respectively, are photoreceptors that bind linear tetrapyrroles and can respond to red and far-red light signals in a reversible manner. A related but distinct photoreceptor candidate, CikA (denoted ScCikA), has been reported to reset the circadian clock in the cyanobacterium Synechococcus elongatus PCC 7942 after a dark pulse. However, recent studies have indicated that ScCikA does not function as a photoreceptor but as a redox sensor. Moreover, the Cys residue that covalently ligates the chromophore in phytochromes is not conserved in the ScCikA protein. On the other hand, the CikA homolog in Synechocystis sp. PCC 6803 (Sir 1969, denoted SyCikA) retains this conserved Cys residue. In our present study, we have isolated the putative chromophore-binding GAF domain of SyCikA from Synechocystis and phycocyanobilin-producing Escherichia coli. Absorption spectra of both preparations showed two peaks in the UV and violet regions. Irradiation of these proteins with violet light yielded a broad peak in a yellow region at the expense of the peaks in the UV and violet regions. Interestingly, successive irradiation with yellow light did not revert these absorption spectra but a partial dark reversion to the original form was detected. These results suggest that SyCikA may function as a violet light sensor in Synechocystis.