Biliverdin binds covalently to Agrobacterium phytochrome Agp1 via its ring a vinyl side chain
Biliverdin binds covalently to Agrobacterium phytochrome Agp1 via its ring a vinyl side chain
复制标题
DOI：
10.1074/jbc.m305563200
复制
发表时间：
2003-09-05
影响因子：
4.8
通讯作者：
Inomata, K
中科院分区：
文献类型：
--
作者：
Lamparter, T;Michael, N;Inomata, K
广泛分布的光敏色素光感受器携带胆色素发色团，其在裂解酶反应期间共价连接到蛋白质。在植物光敏色素中，天然发色团通过其环A亚乙基侧链与蛋白质的所谓GAF结构域内的保守半胱氨酸残基之间的硫醚键偶联。许多细菌光敏色素携带胆绿素作为天然发色团，胆绿素以不同的方式与蛋白质偶联。在根癌农杆菌的光敏色素Agp1中，胆绿素共价连接到靠近N末端的半胱氨酸残基（位置20）。通过测试不同的天然和合成胆绿素衍生物，发现环A乙烯基侧链用于发色团连接。只有那些具有环A乙烯基侧链的胆色素被共价连接，而具有亚乙基或乙基侧链的胆色素以非共价方式结合。然而，属于后一组的藻蓝胆素共价连接到其中半胱氨酸被引入Agp1的GAF结构域（位置249）的突变体。有人提出，位置20和249周围的区域是紧密接触的，并有助于发色团口袋。在竞争实验中，发现藻蓝胆素和胆绿素以与野生型蛋白相似的强度结合。然而，在V249C突变体中，藻蓝胆素的结合比胆绿素强得多。这一发现可以解释为什么在蓝藻光敏色素进化过程中，发色团结合位点从N端交换到GAF结构域。
The widely distributed phytochrome photoreceptors carry a bilin chromophore, which is covalently attached to the protein during a lyase reaction. In plant phytochromes, the natural chromophore is coupled by a thioether bond between its ring A ethylidene side chain and a conserved cysteine residue within the so-called GAF domain of the protein. Many bacterial phytochromes carry biliverdin as natural chromophore, which is coupled in a different manner to the protein. In phytochrome Agp1 of Agrobacterium tumefaciens, biliverdin is covalently attached to a cysteine residue close to the N terminus ( position 20). By testing different natural and synthetic biliverdin derivatives, it was found that the ring A vinyl side chain is used for chromophore attachment. Only those bilins that have ring A vinyl side chain were covalently attached, whereas bilins with an ethylidene or ethyl side chain were bound in a noncovalent manner. Phycocyanobilin, which belongs to the latter group, was however covalently attached to a mutant in which a cysteine was introduced into the GAF domain of Agp1 ( position 249). It is proposed that the regions around positions 20 and 249 are in close contact and contribute both to the chromophore pocket. In competition experiments it was found that phycocyanobilin and biliverdin bind with similar strength to the wild type protein. However, in the V249C mutant, phycocyanobilin bound much more strongly than biliverdin. This finding could explain why during phytochrome evolution in cyanobacteria, the chromophore-binding site swapped from the N terminus into the GAF domain.