T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
J Inorg Biochem. 2017 Dec;177:171-182. doi: 10.1016/j.jinorgbio.2017.09.018. Epub 2017 Sep 22.
The cyanobacterium Synechococcus sp. PCC 7002 produces a monomeric hemoglobin (GlbN) implicated in the detoxification of reactive nitrogen and oxygen species. GlbN contains a b heme, which can be modified under certain reducing conditions. The modified protein (GlbN-A) has one heme-histidine C-N linkage similar to the C-S linkage of cytochrome c. No clear functional role has been assigned to this modification. Here, optical absorbance and NMR spectroscopies were used to compare the reactivity of GlbN and GlbN-A toward nitric oxide (NO). Both forms of the protein are capable of NO dioxygenase activity and both undergo heme bleaching after multiple NO challenges. GlbN and GlbN-A bind NO in the ferric state and form diamagnetic complexes (Fe-NO) that resist reductive nitrosylation to the paramagnetic Fe-NO forms. Dithionite reduction of Fe-NO GlbN and GlbN-A, however, resulted in distinct outcomes. Whereas GlbN-A rapidly formed the expected Fe-NO complex, NO binding to Fe GlbN caused immediate heme loss and, remarkably, was followed by slow heme rebinding and HNO (nitrosyl hydride) production. Additionally, combining Fe GlbN, N-labeled nitrite, and excess dithionite resulted in the formation of Fe-HNO GlbN. Dithionite-mediated HNO production was also observed for the related GlbN from Synechocystis sp. PCC 6803. Although ferrous GlbN-A appeared capable of trapping preformed HNO, the histidine-heme post-translational modification extinguished the NO reduction chemistry associated with GlbN. Overall, the results suggest a role for the covalent modification in Fe GlbNs: protection from NO-mediated heme loss and prevention of HNO formation.
聚球藻 PCC 7002 中的蓝细菌产生单体血红蛋白（GlbN），该血红蛋白与活性氮和氧物种的解毒有关。GlbN 含有一个 b 血红素，该血红素可以在某些还原条件下发生修饰。修饰后的蛋白质（GlbN-A）具有一个血红素-组氨酸 C-N 键，类似于细胞色素 c 的 C-S 键。尚未赋予该修饰明确的功能作用。在这里，使用光学吸收光谱和 NMR 光谱比较了 GlbN 和 GlbN-A 对一氧化氮（NO）的反应性。两种形式的蛋白质都具有 NO 加双氧酶活性，并且在多次 NO 挑战后都会发生血红素漂白。GlbN 和 GlbN-A 在高铁状态下结合 NO 并形成抗还原亚硝化为顺磁性 Fe-NO 形式的顺磁性配合物（Fe-NO）。然而，二硫苏糖醇还原 Fe-NO GlbN 和 GlbN-A 导致了截然不同的结果。虽然 GlbN-A 迅速形成了预期的 Fe-NO 配合物，但 Fe GlbN 与 NO 的结合导致立即失去血红素，并且值得注意的是，随后血红素缓慢重新结合并产生 HNO（亚硝酰氢化物）。此外，将 Fe GlbN、N 标记的亚硝酸盐和过量的二硫苏糖醇结合起来会形成 Fe-HNO GlbN。还观察到二硫苏糖醇介导的 HNO 生成来自 Synechocystis sp. PCC 6803 的相关 GlbN。尽管亚铁 GlbN-A 似乎能够捕获预先形成的 HNO，但组氨酸-血红素的翻译后修饰消除了与 GlbN 相关的 NO 还原化学。总体而言，这些结果表明共价修饰在 Fe GlbNs 中的作用：防止 NO 介导的血红素丢失和防止 HNO 形成。
