Temperature Effects on Agrobacterium Phytochrome Agp1
Temperature Effects on Agrobacterium Phytochrome Agp1
复制标题
DOI：
10.1371/journal.pone.0025977
复制
发表时间：
2011-10-17
期刊：
影响因子：
3.7
通讯作者：
Lamparter, Tilman
中科院分区：
文献类型：
--
作者：
Njimona, Ibrahim;Lamparter, Tilman
光敏色素是广泛分布的胆蛋白光受体，具有保守的N末端发色团结合域。大多数光敏色素带有一个光调控的C-末端，即His激酶或His激酶样区。我们研究了光和温度对根癌农杆菌光敏色素Agp1 His激酶活性的影响。与以前的研究一样，远红光照射后全蛋白的磷酸化活性(红光吸收Pr形式占优势)强于红光照射后全蛋白的磷酸化活性(远红光吸收Pfr形式占主导地位)。当温度从25℃升高到35℃时，脱辅基蛋白、远红光照射的全蛋白和红光照射的全蛋白的磷酸化活性降低；在40℃时，几乎没有检测到任何激酶活性。当温度回到25℃时，在40℃孵育的全蛋白样品的活性几乎完全恢复。UV/可见光光谱表明，蛋白质在45℃以下不变性，然而在50℃时，PFR变性的速度比含有Pr形式的Agp1的黑暗适应样品快。Pr可见光谱不受20-45摄氏度温度的影响，而辐照样品在30-40摄氏度范围内表现出明显的温度效应，在这一范围内，长时间的照射导致PFR光转化为一种名为Prx的新光谱物种。Pfr到Prx的光转化依赖于Agp1的His-Kinase模块；突变株Agp1-M15在40℃下发生了正常的光转化，它缺乏C端的His-Kinase模块，以及一个结构域交换突变体，其中Agp1的His-Kinase模块被另一种根癌农杆菌光敏色素Agp2的组氨酸激酶/反应调节模块所取代。在生理温度范围内依赖于温度的激酶活性和光谱特性表明，Agp1在根癌农杆菌中是一个集成的光和温度传感器。
Phytochromes are widely distributed biliprotein photoreceptors with a conserved N-terminal chromophore-binding domain. Most phytochromes bear a light-regulated C-terminal His kinase or His kinase-like region. We investigated the effects of light and temperature on the His kinase activity of the phytochrome Agp1 from Agrobacterium tumefaciens. As in earlier studies, the phosphorylation activity of the holoprotein after far-red irradiation (where the red-light absorbing Pr form dominates) was stronger than that of the holoprotein after red irradiation (where the far red-absorbing Pfr form dominates). Phosphorylation activities of the apoprotein, far red-irradiated holoprotein, and red-irradiated holoprotein decreased when the temperature increased from 25 degrees C to 35 degrees C; at 40 degrees C, almost no kinase activity was detected. The activity of a holoprotein sample incubated at 40 degrees C was nearly completely restored when the temperature returned to 25 degrees C. UV/visible spectroscopy indicated that the protein was not denatured up to 45 degrees C. At 50 degrees C, however, Pfr denatured faster than the dark-adapted sample containing the Pr form of Agp1. The Pr visible spectrum was unaffected by temperatures of 20-45 degrees C, whereas irradiated samples exhibited a clear temperature effect in the 30-40 degrees C range in which prolonged irradiation resulted in the photoconversion of Pfr into a new spectral species termed Prx. Pfr to Prx photoconversion was dependent on the His-kinase module of Agp1; normal photoconversion occurred at 40 degrees C in the mutant Agp1-M15, which lacks the C-terminal His-kinase module, and in a domain-swap mutant in which the His-kinase module of Agp1 is replaced by the Hiskinase/response regulator module of the other A. tumefaciens phytochrome, Agp2. The temperature-dependent kinase activity and spectral properties in the physiological temperature range suggest that Agp1 serves as an integrated light and temperature sensor in A. tumefaciens.