Abstract：
Light is the crucial environmental signal for desiccation-tolerant cyanobacteria to activate photosynthesis and prepare for desiccation at dawn. However, the photobiological characteristics of desert cyanobacteria adaptation to one of the harshest habitats on Earth remain unresolved. In this study, we surveyed the genome of a subaerial desert cyanobacterium Nostoc flagelliforme and identified two phytochromes and seven cyanobacteriochromes (CBCRs) with one or more bilin-binding GAF (cGMP phosphodiesterase/adenylyl cyclase/FhlA) domains. Biochemical and spectroscopic analyses of 69 purified GAF-containing proteins from recombinant phycocyanobilin (PCB), biliverdin or phycoerythrobilin-producing Escherichia coli indicated that nine of these proteins bind chromophores. Further investigation revealed that 11 GAFs form covalent adducts responsive to near-UV and visible light: eight GAFs contained PCB chromophores, three GAFs contained biliverdin chromophores and one contained the PCB isomer, phycoviolobilin. Interestingly, COO91_03972 is the first-ever reported GAF-only CBCR capable of sensing five wavelengths of light. Bioinformatics and biochemical analyses revealed that residue P132 of COO91_03972 is essential for chromophore binding to dual-cysteine CBCRs. Furthermore, the complement of N. flagelliforme CBCRs is enriched in red light sensors. We hypothesize that these sensors are critical for the acclimatization of N. flagelliforme to weak light environments at dawn.
摘要：
光是耐干燥蓝细菌激活光合作用并为黎明干燥做准备的关键环境信号。然而,沙漠蓝藻适应地球上最恶劣的栖息地之一的光生物学特征仍未解决。在这项研究中,我们调查了一种地下荒漠蓝细菌发菜的基因组，并鉴定了两种植物色素和7种蓝细菌色素（CBCRs），它们具有一个或多个胆素结合GAF（cGMP磷酸二酯酶/腺苷酸环化酶/FhlA）结构域。来自重组藻蓝蛋白（PCB）的69种纯化的含GAF蛋白的生化和光谱分析，胆绿素或产生藻胆素的大肠杆菌表明，这些蛋白质中有9种与发色团结合。进一步的调查显示，11个GAF形成共价加合物响应近紫外线和可见光：8个GAF含有PCB发色团，三个GAF含有胆绿素发色团，一个含有PCB异构体，藻毒素.有趣的是,COO91_03972是有史以来第一个报道的仅GAF的CBCR，能够感应五种波长的光。生物信息学和生物化学分析揭示了COO91_03972的残基P132对于发色团与双半胱氨酸CBCR的结合是必不可少的。此外，鞭毛N.CBCR的补充富含红光传感器。我们假设这些传感器对于鞭毛N.在黎明时适应弱光环境至关重要。
