Phytochromes are a class of photoreceptors found in plants and in some fungi, cyanobacteria, and photoautotrophic and heterotrophic bacteria. Although phytochromes have been structurally characterized in some bacteria, their biological and ecological roles in magnetotactic bacteria remain unexplored. Here, we describe the biochemical characterization of recombinant bacteriophytochrome (BphP) from magnetotactic bacteria Magnetospirillum magneticum AMB-1 (MmBphP). The recombinant MmBphP displays all the characteristic features, including the property of binding to biliverdin (BV), of a genuine phytochrome. Site-directed mutagenesis identified that cysteine-14 is important for chromophore covalent binding and photoreversibility. Arginine-240 and histidine-246 play key roles in binding to BV. The N-terminal photosensory core domain of MmBphP lacking the C-terminus found in other phytochromes is sufficient to exhibit the characteristic red/far-red-light-induced fast photoreversibility of phytochromes. Moreover, our results showed MmBphP is involved in the phototactic response, suggesting its conservative role as a stress protectant. This finding provided us a better understanding of the physiological function of this group of photoreceptors and photoresponse of magnetotactic bacteria.

中文翻译：

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磁性螺旋藻的细菌性植物色素影响光响应行为。

植物色素是在植物和某些真菌，蓝细菌以及光自养和异养细菌中发现的一类光感受器。尽管在某些细菌中已对植物色素进行了结构表征，但它们在趋磁细菌中的生物学和生态作用仍待探索。在这里，我们描述了来自趋磁细菌Magnetospirillum magneticum AMB-1（Mm BphP）的重组细菌植物色素（BphP）的生化特性。重组MmBphP显示出真正的植物色素的所有特征，包括与biliverdin（BV）结合的特性。定点诱变确定半胱氨酸14对发色团共价结合和光可逆性很重要。精氨酸240和组氨酸246在与BV结合中起关键作用。缺少在其他植物色素中发现的C末端的Mm BphP的N末端光敏核心结构域足以表现出特征性的红色/远红光诱导的植物色素快速光可逆性。此外，我们的研究结果表明毫米BphP参与了光战术反应，表明其作为压力保护剂的保守作用。这一发现使我们对这组光感受器的生理功能和趋磁细菌的光反应有了更好的了解。