A second conserved GAF domain cysteine is required for the blue/green photoreversibility of cyanobacteriochrome Tlr0924 from Thermosynechococcus elongatus
A second conserved GAF domain cysteine is required for the blue/green photoreversibility of cyanobacteriochrome Tlr0924 from Thermosynechococcus elongatus
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DOI：
10.1021/bi800088t
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发表时间：
2008-07-08
期刊：
影响因子：
2.9
通讯作者：
Spiller, Susan C.
中科院分区：
文献类型：
--
作者：
Rockwell, Nathan C.;Njuguna, Stephanie Lane;Spiller, Susan C.
光敏色素是广泛存在的红色/远红色光感受器，其利用共价结合在打结的PAS-GAF结构域对内的线性四吡咯（胆色素）发色团。蓝细菌还含有缺乏这种结的光敏色素的远亲，例如与光敏色素相关的蓝细菌色素，其功能是蓝色/绿色可切换的光感受器。在这项研究中，我们的特点是蓝细菌色素Tlr 0924从嗜热cypobacterium Thermosynechococcus elongatus。全长TLR 0924在宽的温度范围内表现出蓝/绿色光转化，包括该生物体的生理相关温度。Tlr 0924的光谱表征表明，其绿色吸收状态与不稳定的、光谱上不同的蓝色吸收物质处于平衡状态。光化学产生的蓝光吸收态与另一种吸收较长波长的物质处于平衡状态，总共有4种状态。Cys 499对于这种行为是必不可少的，因为该残基的诱变导致红色吸收突变胆蛋白。通过吸光度和CD光谱表征C499 D突变蛋白支持其胆色素发色团采用与红光吸收P-r形式的光敏色素类似的构象的结论。我们提出了一个模型的光循环中，Z/E光异构化的15/16键调制形成的Cys 499和C10的发色团之间的可逆硫醚键，蓝/绿色开关的蓝藻色素提供了基础。
Phytochromes are widely occurring red/far-red photoreceptors that utilize a linear tetrapyrrole (bilin) chromophore covalently bound within a knotted PAS-GAF domain pair. Cyanobacteria also contain more distant relatives of phytochromes that lack this knot, such as the phytochrome-related cyanobacteriochromes implicated to function as blue/green switchable photoreceptors. In this study, we characterize the cyanobacteriochrome Tlr0924 from the thermophilic cypobacterium Thermosynechococcus elongatus. Full-length Tlr0924 exhibits blue/green photoconversion across a broad range of temperatures, including physiologically relevant temperatures for this organism. Spectroscopic characterization of Tlr0924 demonstrates that its green-absorbing state is in equilibrium with a labile, spectrally distinct blue-absorbing species. The photochemically generated blue-absorbing state is in equilibrium with another species absorbing at longer wavelengths, giving a total of 4 states. Cys499 is essential for this behavior, because mutagenesis of this residue results in red-absorbing mutant biliproteins. Characterization of the C499D mutant protein by absorbance and CD spectroscopy supports the conclusion that its bilin chromophore adopts a similar conformation to the red-light-absorbing P-r form of phytochrome. We propose a model photocycle in which Z/E photoisomerization of the 15/16 bond modulates formation of a reversible thioether linkage between Cys499 and C10 of the chromophore, providing the basis for the blue/green switching of cyanobacteriochromes.