Structures of cyanobacteriochromes from phototaxis regulators AnPixJ and TePixJ reveal general and specific photoconversion mechanism
Structures of cyanobacteriochromes from phototaxis regulators AnPixJ and TePixJ reveal general and specific photoconversion mechanism
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DOI：
10.1073/pnas.1212098110
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发表时间：
2013-01-15
影响因子：
11.1
通讯作者：
Ikeuchi, Masahiko
中科院分区：
文献类型：
--
作者：
Narikawa, Rei;Ishizuka, Takami;Ikeuchi, Masahiko
蓝细菌色素是蓝细菌四吡咯结合光感受器，其与光敏色素家族的光感受器共享胆色素结合GAF结构域。蓝细菌色素被分为许多具有不同光谱特性的亚类。其中，鱼腥藻PCC 7120和细长热聚球藻BP-1的推定趋光性调节剂PixJ（分别表示为AnPixJ和TePixJ）分别代表了显示红-绿型和蓝/绿型可逆光转换的亚类。在这里，我们确定了AnPixJ GAF域在其红色吸收15 Z状态（Pr）和TePixJ GAF域在其绿色吸收15 E状态（Pg）的晶体结构。这些蛋白质的整体结构彼此相似，也与已知的光敏色素相似。发现的关键差异如下：（i）AnPixJ Pr的发色团是C5-Z，syn/C10-Z，syn/C15-Z，反式构型的藻蓝胆素，TePixJ Pg的发色团是C10-Z，syn/C15-E，反式构型的藻紫胆素，（ii）关键天冬氨酸的侧链与四吡咯环A氢键合，AnPixJ Pr中的B和C以及TePixJ Pg中的吡咯环D，（iii）通过亚类特异性残基（包括AnPixJ中的色氨酸和TePixJ中的半胱氨酸）提供额外的蛋白质-发色团相互作用。根据1.8和2.0埃分辨率下的X射线结构，分别在两种不同的配置中，讨论了C15-Z和C15-E之间的发色团的光异构化后可能的结构变化。
Cyanobacteriochromes are cyanobacterial tetrapyrrole-binding photoreceptors that share a bilin-binding GAF domain with photoreceptors of the phytochrome family. Cyanobacteriochromes are divided into many subclasses with distinct spectral properties. Among them, putative phototaxis regulators PixJs of Anabaena sp. PCC 7120 and Thermosynechococcus elongatus BP-1 (denoted as AnPixJ and TePixJ, respectively) are representative of subclasses showing red-green-type and blue/green-type reversible photoconversion, respectively. Here, we determined crystal structures for the AnPixJ GAF domain in its red-absorbing 15Z state (Pr) and the TePixJ GAF domain in its green-absorbing 15E state (Pg). The overall structure of these proteins is similar to each other and also similar to known phytochromes. Critical differences found are as follows: (i) the chromophore of AnPixJ Pr is phycocyanobilin in a C5-Z, syn/C10-Z, syn/C15-Z, anti configuration and that of TePixJ Pg is phycoviolobilin in a C10-Z, syn/C15-E, anti configuration, (ii) a side chain of the key aspartic acid is hydrogen bonded to the tetrapyrrole rings A, B and C in AnPixJ Pr and to the pyrrole ring D in TePixJ Pg, (iii) additional protein-chromophore interactions are provided by sub-class-specific residues including tryptophan in AnPixJ and cysteine in TePixJ. Possible structural changes following the photoisomerization of the chromophore between C15-Z and C15-E are discussed based on the X-ray structures at 1.8 and 2.0-angstrom resolution, respectively, in two distinct configurations.