MauG, a novel diheme protein required for tryptophan tryptophylquinone biogenesis
MauG, a novel diheme protein required for tryptophan tryptophylquinone biogenesis
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DOI：
10.1021/bi034243q
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发表时间：
2003-06-24
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：
Wang, YT;Graichen, ME;Davidson, VL
脱氮副球藻甲胺脱氢酶(MADH)的生物合成除了编码两个结构蛋白亚基的基因外，还需要四个基因。这些基因产物之前都没有被分离出来。其中一种是MAUG，它与二血红素细胞色素c过氧化物酶序列相似，是合成MADH的色氨酸色氨酸(TTQ)修复基所必需的。建立了MAUG在脱氮假单胞菌中的同源表达系统。它的信号序列被正确处理，并从周质细胞组分中得到纯化。根据推导的序列推测，该蛋白含有两个共价的C型血红素。EPR谱表明，分离的蛋白质含有一个轴对称的高自旋血红素和一个菱形对称的低自旋血红素。低自旋的血红素含有主要和次要的成分，这表明血红素的异质性程度较小。高自旋的亚铁血红素和主要的低自旋亚铁血红素成分都表现出不同于c型亚铁血红素的共振，也不同于已报道的双亚铁血红素细胞色素c过氧化物酶的共振。无论是用c型细胞色素还是用邻二苯甲胺作为电子供体，MAUG的过氧化物酶活性都很弱。完全还原的MAUG可以结合一氧化碳，并可以被氧气重新氧化。在其在TTQ生物发生中的作用的背景下，讨论了MAUG这些不同寻常的特性的相关性。
The biosynthesis of methylamine dehydrogenase (MADH) from Paracoccus denitrificans requires four genes in addition to those that encode the two structural protein subunits. None of these gene products have been previously isolated. One of these, mauG, exhibits sequence similarity to diheme cytochrome c peroxidases and is required for the synthesis of the tryptophan tryptophylquitione (TTQ) prosthetic group of MADH. A system was developed for the homologous expression of MauG in P. denitrificans. Its signal sequence was correctly processed, and it was purified from the periplasmic cell fraction. The protein contains two covalent c-type hemes, as predicted from the deduced sequence. EPR spectroscopy reveals that the protein as isolated possesses about equal amounts of one high-spin heme with axial symmetry and one low-spin heme with rhombic symmetry. The low-spin heme contains a major and minor component suggesting a small degree of heme heterogeneity. The high-spin heme and the major low-spin heme component each exhibit resonances that are atypical of c-type hemes and dissimilar to those reported for diheme cytochrome c peroxidases. MauG exhibited only very weak peroxidase activity when assayed with either c-type cytochromes or o-dianisidine as an electron donor. Fully reduced MauG was shown to bind carbon monoxide and could be reoxidized by oxygen. The relevance of these unusual properties of MauG is discussed in the context of its role in TTQ biogenesis.