CotA, a Multicopper Oxidase from Bacillus pumilus WH4, Exhibits Manganese-Oxidase Activity
作者:Jianmei Su、Peng Bao、Tenglong Bai、Lin Deng、Hui Wu、Fan Liu、Jin He
DOI:10.1371/journal.pone.0060573
日期:——
Multicopper oxidases (MCOs) are a family of enzymes that use copper ions as cofactors to oxidize various substrates. Previous research has demonstrated that several MCOs such as MnxG, MofA and MoxA can act as putative Mn(II) oxidases. Meanwhile, the endospore coat protein CotA from Bacillus species has been confirmed as a typical MCO. To study the relationship between CotA and the Mn(II) oxidation, the cotA gene from a highly active Mn(II)-oxidizing strain Bacillus pumilus WH4 was cloned and overexpressed in Escherichia coli strain M15. The purified CotA contained approximately four copper atoms per molecule and showed spectroscopic properties typical of blue copper oxidases. Importantly, apart from the laccase activities, the CotA also displayed substantial Mn(II)-oxidase activities both in liquid culture system and native polyacrylamide gel electrophoresis. The optimum Mn(II) oxidase activity was obtained at 53°C in HEPES buffer (pH 8.0) supplemented with 0.8 mM CuCl2. Besides, the addition of o-phenanthroline and EDTA both led to a complete suppression of Mn(II)-oxidizing activity. The specific activity of purified CotA towards Mn(II) was 0.27 U/mg. The Km, Vmax and kcat values towards Mn(II) were 14.85±1.17 mM, 3.01×10−6±0.21 M·min−1 and 0.32±0.02 s−1, respectively. Moreover, the Mn(II)-oxidizing activity of the recombinant E. coli strain M15-pQE-cotA was significantly increased when cultured both in Mn-containing K liquid medium and on agar plates. After 7-day liquid cultivation, M15-pQE-cotA resulted in 18.2% removal of Mn(II) from the medium. Furthermore, the biogenic Mn oxides were clearly observed on the cell surfaces of M15-pQE-cotA by scanning electron microscopy. To our knowledge, this is the first report that provides the direct observation of Mn(II) oxidation with the heterologously expressed protein CotA, Therefore, this novel finding not only establishes the foundation for in-depth study of Mn(II) oxidation mechanisms, but also offers a potential biocatalyst for Mn(II) removal.
多铜氧化酶(MCOs)是一个利用铜离子作为辅助因子氧化各种底物的酶家族。以往的研究表明,MnxG、MofA 和 MoxA 等几种多铜氧化酶可作为假定的 Mn(II)氧化酶。同时,芽孢杆菌的内孢子衣壳蛋白 CotA 也被证实是一种典型的 MCO。为了研究 CotA 与锰(II)氧化之间的关系,克隆了高活性锰(II)氧化菌株 Bacillus pumilus WH4 的 cotA 基因,并在大肠杆菌菌株 M15 中进行了过表达。纯化的 CotA 每个分子含有大约四个铜原子,并显示出典型的蓝铜氧化酶光谱特性。重要的是,除了漆酶活性外,CotA 还在液体培养系统和原生聚丙烯酰胺凝胶电泳中显示出大量的锰(II)氧化酶活性。在添加了 0.8 mM CuCl2 的 HEPES 缓冲液(pH 8.0)中,锰(II)氧化酶活性在 53°C 时达到最佳。此外,加入邻菲罗啉和乙二胺四乙酸都会完全抑制锰(II)氧化活性。纯化的 CotA 对锰(II)的比活度为 0.27 U/mg 。对 Mn(II) 的 Km、Vmax 和 kcat 值分别为 14.85±1.17 mM、3.01×10-6±0.21 M-min-1 和 0.32±0.02 s-1。此外,重组大肠杆菌菌株 M15-pQE-cotA 在含锰 K 液体培养基和琼脂平板上的氧化锰(II)活性均显著提高。经过 7 天的液体培养,M15-pQE-cotA 从培养基中清除了 18.2% 的 Mn(II)。此外,通过扫描电子显微镜,我们还在 M15-pQE-cotA 的细胞表面清晰地观察到了生物锰氧化物。据我们所知,这是第一份利用异源表达蛋白 CotA 直接观察锰(II)氧化作用的报告。因此,这一新颖的发现不仅为深入研究锰(II)氧化机制奠定了基础,而且为去除锰(II)提供了一种潜在的生物催化剂。