Biosynthesis of Selenocysteine and Its Incorporation into Protein

正如我们在关于硒在癌症中的作用的项目中所指出的， 健康，硒是人类饮食中必不可少的微量营养素， 许多健康益处。此外，正如在硒在癌症中的作用中所指出的， 我们提出，健康效益在很大程度上是由于 硒蛋白中的硒作为含硒氨基酸存在， 硒代半胱氨酸（Sec）;因此，我们的计划侧重于1）通过Sec是 生物合成并掺入蛋白质中，以及2）开发小鼠模型以评估 硒和特定硒蛋白在人类健康和癌症预防中的作用。期间 在过去的一年里，在我们的项目对生物合成的sec，我们完成并发表了整个 真核生物和古细菌中Sec生物合成途径。两种硒代磷酸盐的作用 合成酶，SPS 1和SPS 2，这两个以前被认为是提供活性硒 在Sec的生物合成中的供体，进一步表征。我们发现SPS 2确实是 一种合成单硒磷酸盐的酶，活性供体，而SPS 1具有不同的作用 可能与硒代谢无关。这些研究解决了一些重要问题， 硒生物学关于硒是如何插入到Sec中以随后并入到 蛋白在过去的几年里，我们还表明， 两种Sec tRNA同种型之一上的34位核糖基部分（命名为Um 34）是 负责合成应激相关的硒蛋白（例如，谷胱甘肽过氧化物酶 1），而缺乏这种修饰的其他同种型参与合成 管家硒蛋白（例如，硫氧还蛋白还原酶1）。因此，我们将重点放在 负责Um 34添加的甲基化酶的鉴定、分离和表征 到Sec tRNA。甲基化酶和潜在甲基化酶的生物信息学分析为我们提供了 与几个候选人，目前正在审查， 使用siRNA技术。此外，我们先前报道了一个命名为SECp 43的因子， 在Um 34合成中发挥作用，在过去的一年里，我们已经产生了条件性敲除 SECp 43小鼠。目前正在对该小鼠进行表征。

As noted in our project on the Role of Selenium in Cancer and Health, selenium is an essential micronutrient in the diet of humans and it has many health benefits. Furthermore, as also noted in the Role of Selenium in Cancer and Health project, we proposed that the health benefits are due in large part to the presence of selenium in selenoproteins as the selenium-containing amino acid, selenocysteine (Sec); and therefore, our program focuses 1) on the means by which Sec is biosynthesized and incorporated into protein and 2) on developing mouse models to assess the role of selenium and specific selenoproteins in human health and cancer prevention. During the past year in our project on the biosynthesis of Sec, we completed and published the entire pathway of Sec biosynthesis in eukaryotes and archaea. The roles of the two selenophosphate synthetases, SPS1 and SPS2, which were both previously thought to provide the active selenium donor in the biosynthesis of Sec, were further characterized. We found that SPS2 is indeed the enzyme that synthesizes monoselenophosphate, the active donor, while SPS1 has a different role that may not be involved in selenium metabolism. These studies resolved important questions in selenium biology on how selenium is inserted into Sec to be subsequently incorporated into protein. We have also shown in the last few years that the methyl group attached to the ribosyl moiety at position 34 on one of the two Sec tRNA isoforms (designated Um34) is responsible for the synthesis of stress-related selenoproteins (e.g., glutathione peroxidase 1), while the other isoform lacking this modification is involved in the synthesis of housekeeping selenoproteins (e.g., thioredoxin reductase 1). We are therefore focusing on the identification, isolation and characterization of the methylase responsible for Um34 addition to Sec tRNA. Bioinformatic analysis of methylases and potential methylases have provided us with several candidates that are currently being examined by knocking down their expression using siRNA technology. In addition, we previously reported that a factor designated SECp43 had a role in Um34 synthesis, and in the past year, we have generated the conditional knockout mouse of SECp43. This mouse is currently being characterized.