CAU & ACC Joint Laboratory of Space Food, College of Food Science and Nutritional Engineering, China Agricultural University, and Key Laboratory of Functional Dairy, Ministry of Education, Beijing 100083, China.
Free Radic Biol Med. 2012 Jul 15;53(2):375-82. doi: 10.1016/j.freeradbiomed.2012.05.003. Epub 2012 May 8.
Plant ferritin is a naturally occurring heteropolymer in plastids, where Fe(2+) is oxidatively deposited into the protein. However, the effect of this process on the coexistence of DNA and plant ferritin in the plastids is unknown. To investigate this effect, we built a system in which various plant ferritins and DNA coexist, followed by treatment with ferrous ions under aerobic conditions. Interestingly, naturally occurring soybean seed ferritin (SSF), a heteropolymer with an H-1/H-2 ratio of 1 to 1 in the apo form, completely protected DNA from oxidative damage during iron oxidative deposition into protein, and a similar result was obtained with its recombinant form, but not with its homopolymeric counterparts, apo rH-1 and apo rH-2. We demonstrate that the difference in DNA protection between heteropolymeric and homopolymeric plant ferritins stems from their different strategies to control iron chemistry during the above oxidative process. For example, the detoxification reaction occurs only in the presence of apo heteropolymeric SSF (hSSF), thereby preventing the production of hydroxyl radicals. In contrast, hydroxyl radicals are apparently generated via the Fenton reaction when apo rH-1 or rH-2 is used instead of apo hSSF. Thus, a combination of H-1 and H-2 subunits in hSSF seems to impart a unique DNA-protective function to the protein, which was previously unrecognized. This new finding advances our understanding of the structure and function of ferritin and of the widespread occurrence of heteropolymeric plant ferritin in nature.
植物铁蛋白是质体中天然存在的异多聚体，Fe(2+)在此被氧化沉积到蛋白中。然而，这一过程对质体中 DNA 和植物铁蛋白共存的影响尚不清楚。为了研究这一影响，我们构建了一个系统，使各种植物铁蛋白和 DNA 共存，然后在有氧条件下用亚铁离子处理。有趣的是，天然存在的大豆种子铁蛋白（SSF），在apo 形式下 H-1/H-2 比为 1:1 的异多聚体，在铁氧化沉积到蛋白的过程中完全保护了 DNA 免受氧化损伤，其重组形式也得到了类似的结果，但它的同聚体 apo rH-1 和 apo rH-2 则没有。我们证明，异多聚体和同聚体植物铁蛋白在 DNA 保护方面的差异源于它们在上述氧化过程中控制铁化学的不同策略。例如，只有在 apo 异多聚体 SSF（hSSF）存在的情况下，解毒反应才会发生，从而防止羟基自由基的产生。相比之下，当使用 apo rH-1 或 rH-2 代替 apo hSSF 时，羟基自由基显然是通过 Fenton 反应产生的。因此，hSSF 中 H-1 和 H-2 亚基的结合似乎赋予了该蛋白一种独特的 DNA 保护功能，这是以前未被认识到的。这一新发现增进了我们对铁蛋白结构和功能的理解，以及自然界中广泛存在的异多聚体植物铁蛋白的理解。
