Crystal structure of phycocyanobilin:ferredoxin oxidoreductase in complex with biliverdin IXα, a key enzyme in the biosynthesis of phycocyanobilin
Crystal structure of phycocyanobilin:ferredoxin oxidoreductase in complex with biliverdin IXα, a key enzyme in the biosynthesis of phycocyanobilin
复制标题
DOI：
10.1073/pnas.0507266103
复制
发表时间：
2006-01-03
影响因子：
11.1
通讯作者：
Fukuyama, K
中科院分区：
文献类型：
--
作者：
Hagiwara, Y;Sugishima, M;Fukuyama, K
植物胆素（高等植物、藻类和蓝细菌中的光捕获和光感受器色素）是由胆绿素 IX α (BV) 通过铁氧还蛋白依赖性胆素还原酶 (FDBR) 合成的。 FDBR 中的藻蓝蛋白：铁氧还蛋白氧化还原酶 (PcyA) 是一类新型自由基酶，既不需要辅因子，也不需要金属，利用铁氧还蛋白的四个电子连续还原 BV 的 D 环和 A 环的乙烯基，产生藻蓝蛋白（植物胆素之一）。我们已经确定了集胞藻 (Synechocystis sp.) 中 PcyA 的晶体结构。 PCC 6803 与 BV 形成复合物，揭示了 FDBR 家族成员的第一个三级结构。 PcyA 折叠成三层 α/β/α 夹心结构，其中环状构象的 BV 位于 β 片层和 C 端 α 螺旋之间。 PcyA 表面上 BV 分子附近的碱性斑块可能为酸性铁氧还蛋白提供结合位点，从而允许电子直接转移至 BV。 BV 的方向通过多种亲水相互作用和 PcyA 的 BV 结合袋的形状在 PcyA 中明确固定。我们提出了控制 D 环和 A 环顺序还原的机制，其中位于两个还原位点之间的 Asp-105 将通过在反应过程中改变其构象来发挥核心作用。基于PcyA结构的其他FDBR的同源建模与先前的遗传和生化数据非常吻合，从而为FDBR的反应机制提供了结构基础。
Phytobilins (light harvesting and photoreceptor pigments in higher plants, algae, and cyanobacteria) are synthesized from biliverdin IX alpha (BV) by ferredoxin-dependent bilin reductases (FDBRs). Phycocyanobilin:ferredoxin oxidoreductase (PcyA), one such FDBR, is a new class of radical enzymes that require neither cofactors nor metals and serially reduces the vinyl group of the D-ring and A-ring of BV using four electrons from ferredoxin to produce phycocyanobilin, one of the phytobilins. We have determined the crystal structure of PcyA from Synechocystis sp. PCC 6803 in complex with BV, revealing the first tertiary structure of an FDBR family member. PcyA is folded in a three-layer alpha/beta/alpha sandwich structure, in which BV in a cyclic conformation is positioned between the beta-sheet and C-terminal a-helices. The basic patch on the PcyA surface near the BV molecule may provide a binding site for acidic ferredoxin, allowing direct transfer of electrons to BV. The orientation of BV is definitely fixed in PcyA by several hydrophilic interactions and the shape of the BV binding pocket of PcyA. We propose the mechanism by which the sequential reduction of the D- and A-rings is controlled, where Asp-105, located between the two reduction sites, would play the central role by changing its conformation during the reaction. Homology modeling of other FDBRs based on the PcyA structure fits well with previous genetic and biochemical data, thereby providing a structural basis for the reaction mechanism of FDBRs.