Systems level understanding of selenoprotein biosynthesis

硒（Se）是一种微量元素，在大脑功能、男性生殖和免疫功能等过程中发挥作用。在哺乳动物中，硒以硒半胱氨酸（Sec）残基的形式存在于蛋白质中，是一种必需元素。Sec是遗传密码中的第21个氨基酸，响应UGA密码子共翻译插入蛋白质中，与终止蛋白质合成竞争。一些硒蛋白基因的突变和单核苷酸多态性与疾病有关。我们之前开发的工具可以有效地鉴定硒蛋白基因。利用这些工具，我们鉴定了人类和小鼠硒蛋白（硒蛋白质组）。我们进一步开发了支持硒、硒和硒蛋白合成综合分析的方法，最值得注意的是核糖体分析。我们准备通过解决该领域的关键问题，从这个基础中受益。首先，我们将描述Sec插入和终止蛋白质合成之间竞争的影响。UGA密码子上的Sec插入与终止相竞争，表明大量截断的蛋白质被合成，然后必须被细胞降解。器官间硒代谢的差异进一步加剧了这一点。我们将利用核糖体分析来表征小鼠各器官中硒蛋白的合成，定义硒蛋白同型体，并表征截短的硒蛋白的命运。其次，我们将以硒蛋白、组织和硒饮食特异性的方式确定不同器官中硒蛋白合成的速率和特征。利用活体动物的核糖体分析，我们将确定器官和个体硒蛋白水平上的硒蛋白合成速率，表征膳食硒对硒蛋白合成的调节，并在转录丰度和硒蛋白合成水平上研究硒蛋白表达的平行调节。

Selenium (Se) is a trace element with roles in processes, such as brain function, male reproduction, and immune function. In mammals, Se is an essential element due to its presence in proteins in the form of selenocysteine (Sec) residue. Sec is known as the 21st amino acid in the genetic code and is co-translationally inserted into proteins in response to UGA codons, in competition with termination of protein synthesis. Mutations and single nucleotide polymorphisms in several selenoprotein genes have been associated with disease. We previously developed tools that allow efficient identification of selenoprotein genes. Using these tools, we identified sets of human and mouse selenoproteins (selenoproteomes). We further developed approaches that support integrative analyses of Se, Sec, and selenoprotein synthesis, most notably ribosome profiling. We are poised to benefit from this foundation by addressing critical questions in the field. First, we will characterize the impact of competition between Sec insertion and termination of protein synthesis. Sec insertion at UGA codons competes with termination, suggesting that large amounts of truncated proteins are synthesized and then must be degraded by the cells. This is further exacerbated by differences in Se metabolism among organs. We will utilize ribosome profiling to characterize selenoprotein synthesis in various organs of mice, define selenoprotein isoforms, and characterize the fate of truncated selenoproteins. Second, we will determine the rates and features of selenoprotein synthesis in various organs in a selenoprotein-, tissue-, and selenium diet-specific manner. Using ribosome profiling in live animals, we will determine the rates of selenoprotein synthesis at the level of organs and individual selenoproteins, characterize regulation of selenoprotein synthesis by dietary selenium, and examine parallel regulation of selenoprotein expression at the level of transcript abundance and selenoprotein synthesis in mouse organs.