Evidence for redox cooperativity between c-type hemes of MauG which is likely coupled to oxygen activation during tryptophan tryptophylquinone biosynthesis
Evidence for redox cooperativity between c-type hemes of MauG which is likely coupled to oxygen activation during tryptophan tryptophylquinone biosynthesis
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DOI：
10.1021/bi052000n
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发表时间：
2006-01-24
期刊：
影响因子：
2.9
通讯作者：
Davidson, VL
中科院分区：
文献类型：
--
作者：
Li, XH;Feng, ML;Davidson, VL
mag是一种新的42 kDa二血红素蛋白，是甲胺脱氢酶的假基色氨酸色氨酸醌的生物合成所必需的。描述了两种c型血红素的可见吸收和共振拉曼光谱特性以及MauG的整体氧化还原特性。低自旋氧化血红素和还原血红素的Soret峰吸收最大值分别为403和418 nm，高自旋血红素的Soret峰吸收最大值分别为389和427 nm。氧化MauG的共振拉曼光谱在1503和1588 cm（-1）处显示出一组标记带，其频率与c型血红素蛋白的nu(3)和nu(2)带相似，具有比司替丁配位。另一组标记带位于1478和1570 cm（-1）处，是高自旋血红素的特征。mag的光谱滴定得到了两个不同的氧化还原中点电位（E-m）值-159和-244 mV。然而，位于1478和1503 cm（-1）的两个nu(3)带在还原后分别移到1467和1492 cm(-1)，吸收光谱中低自旋和高自旋血红素的Soret峰也是如此。因此，在氧化还原滴定过程中，具有不同光谱性质的两种血红素被还原和氧化到大约相同的程度。这表明高自旋血红素和低自旋血红素具有相似的固有E-m值，但表现出负的氧化还原协同性。在MauG的第一个单电子还原后，血红素之间的电子平衡。这使得mag的第二次单电子还原更加困难。因此，两个E-m值并不描述不同血红素的氧化还原性质，而是描述具有两个等效血红素的二血红素系统的第一次和第二次单电子还原。讨论了这些发现的结构和力学意义。
MauG is a novel 42 kDa diheme protein which is required for the biosynthesis of tryptophan tryptophylquinone, the prosthetic group of methylamine dehydrogenase. The visible absorption and resonance Raman spectroscopic properties of each of the two c-type hemes and the overall redox properties of MauG are described. The absorption maxima for the Soret peaks of the oxidized and reduced hemes are 403 and 418 nm for the low-spin heme and 389 and 427 nm for the high-spin heme, respectively. The resonance Raman spectrum of oxidized MauG exhibits a set of marker bands at 1503 and 1588 cm(-1) which exhibit frequencies similar to those of the nu(3) and nu(2) bands of c-type heme proteins with bishistidine coordination. Another set of marker bands at 1478 and 1570 cm(-1) is characteristic of a high-spin heme. Two distinct oxidation-reduction midpoint potential (E-m) values of -159 and -244 mV are obtained from spectrochemical titration of MauG. However, the two nu(3) bands located at 1478 and 1503 cm(-1) shift together to 1467 and 1492 cm(-1), respectively, upon reduction, as do the Soret peaks of the low- and high-spin hemes in the absorption spectrum. Thus, the two hemes with distinct spectral properties are reduced and oxidized to approximately the same extent during redox titrations. This indicates that the high- and low-spin hemes have similar intrinsic E-m values but exhibit negative redox cooperativity. After the first one-electron reduction of MauG, the electron equilibrates between hemes. This makes the second one-electron reduction of MauG more difficult. Thus, the two E-m values do not describe redox properties of distinct hemes, but the first and second one-electron reductions of a diheme system with two equivalent hemes. The structural and mechanistic implications of these findings are discussed.