Unique Electronic Structures of the Highly Ruffled Hemes in Heme-Degrading Enzymes ofStaphylococcus aureus, IsdG and IsdI, by Resonance Raman and Electron Paramagnetic Resonance Spectroscopies
Unique Electronic Structures of the Highly Ruffled Hemes in Heme-Degrading Enzymes ofStaphylococcus aureus, IsdG and IsdI, by Resonance Raman and Electron Paramagnetic Resonance Spectroscopies
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通过共振拉曼和电子顺磁共振光谱研究金黄色葡萄球菌血红素降解酶 IsdG 和 IsdI 中高度褶皱血红素的独特电子结构
DOI：
10.1021/acs.biochem.0c00731
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发表时间：
2020
期刊：
影响因子：
2.9
通讯作者：
Ikeda-Saito Masao
中科院分区：
文献类型：
--
作者：
Takahashi Satoshi;Nambu Shusuke;Matsui Toshitaka;Fujii Hiroshi;Ishikawa Haruto;Mizutani Yasuhisa;Tsumoto Kouhei;Ikeda-Saito Masao
金黄色葡萄球菌利用IsdG和IsdI将血红素转化为葡萄球菌素异构体、15-氧代-β-胆红素和5-氧代-δ-胆红素、甲醛和铁的混合物。在血红素-IsdI和IsdG复合物中发现的高度皱褶的血红素被认为是独特的血红素降解产物的原因。我们采用共振拉曼（RR）和电子顺磁共振（EPR）光谱研究血红素结合到IsdG和IsdI的配位和电子结构。与IsdG和IsdI复合的血红素由中性组氨酸配位。反式配体是两种蛋白质的铁碱性形式的氢氧化物。在pH 6.0的铁中性形式中，血红素与水六配位作为IsdG的第六配体，并且在IsdI的五配位和六配位物种的混合物中。在亚铁CO结合形式中，CO与远端残基强烈氢键结合。标记线ν 2和ν3的出现频率与其他具有平面血红素的蛋白质不同。氢氧化铁和氰化铁态的EPR谱可以用d电子构型（dxy）2（dxz，dyz）3和（dxz，dyz）4（dxy）1的热混合来解释。对于氰化铁形式，后者的分数变得更大。在pH6.0的铁中性态，高、中自旋组态的量子力学混合可以解释RR谱中ν 2和ν 3的特殊频率.由IsdG和IsdI施加的血红素皱褶产生血红素的独特电子结构，其预期调节血红素氧化的第一和随后的步骤。
Staphylococcus aureususes IsdG and IsdI to convert heme into a mixture of staphylobilin isomers, 15-oxo-β-bilirubin and 5-oxo-δ-bilirubin, formaldehyde, and iron. The highly ruffled heme found in the heme-IsdI and IsdG complexes has been proposed to be responsible for the unique heme degradation products. We employed resonance Raman (RR) and electron paramagnetic resonance (EPR) spectroscopies to examine the coordination and electronic structures of heme bound to IsdG and IsdI. Heme complexed to IsdG and IsdI is coordinated by a neutral histidine. The trans ligand is hydroxide in the ferric alkaline form of both proteins. In the ferric neutral form at pH 6.0, heme is six-coordinated with water as the sixth ligand for IsdG and is in the mixture of the five-coordinated and six-coordinated species for IsdI. In the ferrous CO-bound form, CO is strongly hydrogen bonded with a distal residue. The marker lines, ν2and ν3, appear at frequencies that are distinct from other proteins having planar hemes. The EPR spectra for the ferric hydroxide and cyanide states might be explained by assuming the thermal mixing of thed-electron configurations, (dxy)2(dxz,dyz)3and (dxz,dyz)4(dxy)1. The fraction for the latter becomes larger for the ferric cyanide form. In the ferric neutral state at pH 6.0, the quantum mechanical mixing of the high and intermediate spin configurations might explain the peculiar frequencies of ν2and ν3in the RR spectra. The heme ruffling imposed by IsdG and IsdI gives rise to unique electronic structures of heme, which are expected to modulate the first and subsequent steps of the heme oxygenation.