Crystal structure and redox properties of a novel cyanobacterial heme protein with a His/Cys heme axial ligation and a Per-Arnt-Sim (PAS)-like domain
Crystal structure and redox properties of a novel cyanobacterial heme protein with a His/Cys heme axial ligation and a Per-Arnt-Sim (PAS)-like domain
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DOI：
10.1074/jbc.m116.746263
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发表时间：
2017-04
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通讯作者：
T. Motomura;M. Suga;R. Hienerwadel;A. Nakagawa;Thanh-Lan Lai;W. Nitschke;Takahiro Kuma;M. Sugiura;A. Boussac;Jian-Ren Shen
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作者：
T. Motomura;M. Suga;R. Hienerwadel;A. Nakagawa;Thanh-Lan Lai;W. Nitschke;Takahiro Kuma;M. Sugiura;A. Boussac;Jian-Ren Shen
光系统II催化光诱导的水氧化，导致产生对维持地球上的有氧生命必不可少的双氧。光系统II反应中心分别由psbA和psbD基因编码的D1和D2蛋白组成。在蓝藻中，不同的psbA基因存在于基因组中。嗜热蓝藻长热共生球菌含有psbA1、psbA2和psbA3 3个psbA基因，在一个只表达psbA2基因的菌株中发现了一个新的c型血红素蛋白Tll0287，但其结构和功能尚不清楚。在这里，我们以2.0 Å分辨率解决了Tll0287的晶体结构。Tll0287的整体结构与一些具有Per-Arnt-Sim-like结构域的激酶和传感器蛋白相似，而与其他c型细胞色素不同。血红素的第五和第六轴配体是Cys和His，而不是大多数c型血红素的His/Met或His/His配体对。与正常氢电极相比，Tll0287在pH值高于7.5时的氧化还原电位为- 255±20 mV。在此pH值以下，在15℃下，E½增加了约57 mV/pH单位，表明pKred = 7.2±0.3的可质子基团参与。从psbA2表达的环境条件、系统发育分析、结构和序列同源性等方面讨论了Tll0287在微氧条件下作为氧化还原传感器或h2s氧化系统的细胞色素亚基的可能功能。
Photosystem II catalyzes light-induced water oxidation leading to the generation of dioxygen indispensable for sustaining aerobic life on Earth. The Photosystem II reaction center is composed of D1 and D2 proteins encoded by psbA and psbD genes, respectively. In cyanobacteria, different psbA genes are present in the genome. The thermophilic cyanobacterium Thermosynechococcus elongatus contains three psbA genes: psbA1, psbA2, and psbA3, and a new c-type heme protein, Tll0287, was found to be expressed in a strain expressing the psbA2 gene only, but the structure and function of Tll0287 are unknown. Here we solved the crystal structure of Tll0287 at a 2.0 Å resolution. The overall structure of Tll0287 was found to be similar to some kinases and sensor proteins with a Per-Arnt-Sim-like domain rather than to other c-type cytochromes. The fifth and sixth axial ligands for the heme were Cys and His, instead of the His/Met or His/His ligand pairs observed for most of the c-type hemes. The redox potential, E½, of Tll0287 was −255 ± 20 mV versus normal hydrogen electrode at pH values above 7.5. Below this pH value, the E½ increased by ≈57 mV/pH unit at 15 °C, suggesting the involvement of a protonatable group with a pKred = 7.2 ± 0.3. Possible functions of Tll0287 as a redox sensor under microaerobic conditions or a cytochrome subunit of an H2S-oxidizing system are discussed in view of the environmental conditions in which psbA2 is expressed, as well as phylogenetic analysis, structural, and sequence homologies.