Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195, United States.
Department of Chemistry & Chemical Biology, University of California , 5200 North Lake Road, Merced, California 95343, United States.
J Am Chem Soc. 2017 Jul 5;139(26):8868-8877. doi: 10.1021/jacs.7b02277. Epub 2017 Jun 22.
Manganese-oxide minerals (MnO) are widely distributed over the Earth's surface, and their geochemical cycling is globally important. A multicopper oxidase (MCO) MnxG protein from marine Bacillus bacteria plays an essential role in producing MnO minerals by oxidizing Mn(aq) at rates that are 3 to 5 orders of magnitude faster than abiotic rates. The MnxG protein is isolated as part of a multiprotein complex denoted as "Mnx" that includes accessory protein subunits MnxE and MnxF, with an estimated stoichiometry of MnxEFG and corresponding molecular weight of ≈211 kDa. Herein, we report successful expression and isolation of the MCO MnxG protein without the EF hexamer. This isolated MnxG shows activity for Mn(aq) oxidation to form manganese oxides. The complement of paramagnetic Cu(II) ions in the Mnx protein complex was examined by electron paramagnetic resonance (EPR) spectroscopy. Two distinct classes of type 2 Cu sites were detected. One class of Cu(II) site (denoted as T2Cu-A), located in the MnxG subunit, is identified by the magnetic parameters g = 2.320 and A = 510 MHz. The other class of Cu(II) sites (denoted as T2Cu-B) is characterized by g = 2.210 and A = 615 MHz and resides in the putative hexameric MnxEF subunit. These different magnetic properties correlate with the differences in the reduction potentials of the respective Cu(II) centers. These studies provide new insights into the molecular mechanism of manganese biomineralization.
氧化锰矿物 (MnO) 广泛分布于地球表面，其地球化学循环具有全球性意义。海洋芽孢杆菌中的一种多铜氧化酶 (MCO) MnxG 蛋白通过氧化 Mn(aq)发挥着至关重要的作用，其氧化速率比非生物速率快 3 到 5 个数量级，从而产生 MnO 矿物。MnxG 蛋白作为一个多蛋白复合物的一部分被分离出来，该复合物被称为“Mnx”，其中包括辅助蛋白亚基 MnxE 和 MnxF，其估计化学计量比为 MnxEFG，分子量约为 211 kDa。在此，我们报告了成功表达和分离不包含 EF 六聚体的 MCO MnxG 蛋白。这种分离的 MnxG 蛋白显示出将 Mn(aq)氧化为锰氧化物的活性。通过电子顺磁共振 (EPR) 光谱检查了 Mnx 蛋白复合物中顺磁 Cu(II) 离子的含量。检测到两种不同类型的 2 型 Cu 位点。一种类型的 Cu(II)位点（表示为 T2Cu-A）位于 MnxG 亚基中，其磁参数为 g = 2.320 和 A = 510 MHz。另一种类型的 Cu(II)位点（表示为 T2Cu-B）的特征为 g = 2.210 和 A = 615 MHz，位于假定的六聚体 MnxEF 亚基中。这些不同的磁性性质与相应 Cu(II)中心的还原电势差异相关。这些研究为锰生物矿化的分子机制提供了新的见解。
