Phytochrome from Agrobacterium tumefaciens has unusual spectral properties and reveals an N-terminal chromophore attachment site
Phytochrome from Agrobacterium tumefaciens has unusual spectral properties and reveals an N-terminal chromophore attachment site
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DOI：
10.1073/pnas.152263999
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发表时间：
2002-09-03
影响因子：
11.1
通讯作者：
Esteban, B
中科院分区：
文献类型：
--
作者：
Lamparter, T;Michael, N;Esteban, B
光敏色素是在植物和细菌中发现的具有胆色素发色团的光致变色光感受器。土壤细菌根癌农杆菌含有两个编码光敏色素同源蛋白的基因，称为农杆菌光敏色素 1 和 2（Agp1 和 Agp2）。为了分析其生化和光谱特性，从大肠杆菌过表达子的克隆中纯化了 Agp1。该蛋白质与生色团藻蓝蛋白和胆绿素（假定的天然生色团）组装成光活性全蛋白种类。与其他细菌光敏色素一样，Agp1 充当光调节组氨酸激酶。 Agp1 的胆绿素加合物代表了一种以前未表征的光敏色素光感受器类型，因为从远红光吸收形式到红光吸收形式的光回复效率非常低，这一特征与快速暗回复相结合。胆绿素与蛋白质共价结合；封闭实验和定点诱变鉴定出 20 位的 Cys 作为结合位点。这个特定位置位于植物和一些蓝藻光敏色素附着其发色团的区域之外，因此代表了以前未表征的结合位点。序列比较表明 Cys-20 周围的区域是光敏色素中的 D 环结合基序。
Phytochromes are photochromic photoreceptors with a bilin chromophore that are found in plants and bacteria. The soil bacterium Agrobacterium tumefaciens contains two genes that code for phytochrome-homologous proteins, termed Agrobacterium phytochrome 1 and 2 (Agp1 and Agp2). To analyze its biochemical and spectral properties, Agp1 was purified from the clone of an E coli overexpressor. The protein was assembled with the chromophores phycocyanobilin and biliverdin, which is the putative natural chromophore, to photoactive holoprotein species. Like other bacterial phytochromes, Agp1 acts as light-regulated His kinase. The biliverdin adduct of Agp1 represents a previously uncharacterized type of phytochrome photoreceptor, because photoreversion from the far-red absorbing form to the red-absorbing form is very inefficient, a feature that is combined with a rapid dark reversion. Biliverdin bound covalently to the protein; blocking experiments and site-directed mutagenesis identified a Cys at position 20 as the binding site. This particular position is outside the region where plant and some cyanobacterial phytochromes attach their chromophore and thus represents a previously uncharacterized binding site. Sequence comparisons imply that the region around Cys-20 is a ring D binding motif in phytochromes.