Hydrogen peroxide-mediated conversion of coproheme to heme b by HemQ-lessons from the first crystal structure and kinetic studies
Hydrogen peroxide-mediated conversion of coproheme to heme b by HemQ-lessons from the first crystal structure and kinetic studies
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DOI：
10.1111/febs.13930
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发表时间：
2016-12-01
期刊：
影响因子：
5.4
通讯作者：
Obinger, Christian
中科院分区：
文献类型：
--
作者：
Hofbauer, Stefan;Mlynek, Georg;Obinger, Christian
在革兰氏阳性细菌中，血红素的生物合成遵循最近被描述的依赖于共比例卟啉的途径，其中hemQ催化辅素脱羧基为血红素b。在这里，我们提出了第一个晶体结构(来自单核细胞增生性李斯特氏菌的同源五元辅素-hemQ)，以及辅素转化为血红素b的过程，随后进行了UV-Vis和共振拉曼光谱以及质谱学的研究。HemQ的铁五配位辅位素铁与中性近端组氨酸H174弱结合。在休眠状态的晶体结构中，远端的Q187(保存在Firmicuts hemQ中)与丙酸p2形成氢键，疏水的远端空腔中缺少溶剂水分子。两个H_2O_2分子被证明是丙酸酯p2和p_4脱羧基所必需的，从而形成相应的血红素b的乙烯基团。整个反应相对缓慢(在pH 7.0时，k(CAT)/K-M=1.8×10~(2)M~(-1)·s~(-1))，并与三丙酸酯中间体以分步方式发生。我们提出了辅蛋白和蛋白质之间的非共价相互作用，并提出了一个两步反应机制。此外，还比较了协同素-hemQ的结构与系统发育相关的含亚氯酸根的亚氯酸盐歧化酶的结构。
Heme biosynthesis in Gram-positive bacteria follows a recently described coproporphyrin-dependent pathway with HemQ catalyzing the decarboxylation of coproheme to heme b. Here we present the first crystal structure of a HemQ (homopentameric coproheme-HemQ from Listeria monocytogenes) at 1.69 angstrom resolution and the conversion of coproheme to heme b followed by UV-vis and resonance Raman spectroscopy as well as mass spectrometry. The ferric five-coordinated coproheme iron of HemQ is weakly bound by a neutral proximal histidine H174. In the crystal structure of the resting state, the distal Q187 (conserved in Firmicutes HemQ) is H-bonded with propionate p2 and the hydrophobic distal cavity lacks solvent water molecules. Two H2O2 molecules are shown to be necessary for decarboxylation of the propionates p2 and p4, thereby forming the corresponding vinyl groups of heme b. The overall reaction is relatively slow (k(cat)/K-M = 1.8 x 10(2) M-1.s(-1) at pH 7.0) and occurs in a stepwise manner with a three-propionate intermediate. We present the noncovalent interactions between coproheme and the protein and propose a two-step reaction mechanism. Furthermore, the structure of coproheme-HemQ is compared to that of the phylogenetically related heme b-containing chlorite dismutases.