Protein-folding location can regulate manganese-binding versus copper- or zinc-binding
Protein-folding location can regulate manganese-binding versus copper- or zinc-binding
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DOI：
10.1038/nature07340
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发表时间：
2008-10-23
期刊：
影响因子：
64.8
通讯作者：
Robinson, Nigel J.
中科院分区：
文献类型：
--
作者：
Tottey, Steve;Waldron, Kevin J.;Robinson, Nigel J.
至少四分之一的蛋白质需要金属(1,2)。尽管金属伴侣 (3-8) 将正确的金属插入到一些蛋白质中，但绝大多数蛋白质尚未发现它们，并且观点认为大多数金属蛋白质直接从细胞库中获取金属。然而，一些金属与蛋白质形成的复合物比其他金属更稳定。例如，如 Irving Williams 系列 (9) 中所述，Cu2+ 和 Zn2+ 通常形成比 Mn2+ 更稳定的络合物。因此，尚不清楚什么细胞机制管理大多数新生蛋白质的金属获取。为了研究这个问题，我们在蓝藻集胞藻 PCC 6803 的周质中鉴定出了最丰富的 Cu2+-蛋白 CucA (Cu2+- cupin A) 和最丰富的 Mn2+- 蛋白 MncA (Mn2+- cupin A)。这些新鉴定的蛋白中的每一种都通过 cupin 折叠内相同的配体结合其各自的金属。与 Irving-Williams 系列一致，MncA 仅在 Mn2+ 摩尔数超过 Cu2+ 或 Zn2+ 至少 10(4) 倍摩尔过量的溶液中折叠后才与 Mn2+ 结合。然而，一旦 MncA 与 Mn2+ 结合，该金属就不会与 Cu2+ 交换。 MncA 和 CucA 具有分别通往周质、Tat 和 Sec 的不同输出途径的信号肽。 Tat 途径的输出允许 MncA 在细胞质中折叠，细胞质仅包含紧密结合的铜或 Zn2+（参考文献 10-12），但含有微摩尔的 Mn2+（参考文献 13）。相反，CucA 在周质中折叠以获得 Cu2+。这些结果揭示了一种机制，其中蛋白质折叠的区室超越其结合偏好以控制其金属含量。他们解释了为什么细胞质必须只含有紧密结合和缓冲的铜和 Zn2+。
Metals are needed by at least one-quarter of all proteins(1,2). Although metallochaperones(3-8) insert the correct metal into some proteins, they have not been found for the vast majority, and the view is that most metalloproteins acquire their metals directly from cellular pools. However, some metals form more stable complexes with proteins than do others. For instance, as described in the Irving Williams series(9), Cu2+ and Zn2+ typically form more stable complexes than Mn2+. Thus it is unclear what cellular mechanisms manage metal acquisition by most nascent proteins. To investigate this question, we identified the most abundant Cu2+-protein, CucA (Cu2+- cupin A), and the most abundant Mn2+- protein, MncA (Mn2+- cupin A), in the periplasm of the cyanobacterium Synechocystis PCC 6803. Each of these newly identified proteins binds its respective metal via identical ligands within a cupin fold. Consistent with the Irving - Williams series, MncA only binds Mn2+ after folding in solutions containing at least a 10(4) times molar excess of Mn2+ over Cu2+ or Zn2+. However once MncA has bound Mn2+, the metal does not exchange with Cu2+. MncA and CucA have signal peptides for different export pathways into the periplasm, Tat and Sec respectively. Export by the Tat pathway allows MncA to fold in the cytoplasm, which contains only tightly bound copper or Zn2+ ( refs 10-12) but micromolar Mn2+ ( ref. 13). In contrast, CucA folds in the periplasm to acquire Cu2+. These results reveal a mechanism whereby the compartment in which a protein folds overrides its binding preference to control its metal content. They explain why the cytoplasm must contain only tightly bound and buffered copper and Zn2+.