Selenium. Role of the essential metalloid in health.
Selenium. Role of the essential metalloid in health.
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DOI：
10.1007/978-94-007-7500-8_16
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Berry, Marla J
中科院分区：
文献类型：
--
作者：
Kurokawa, Suguru;Berry, Marla J
硒是哺乳动物必需的微量营养素，但过量也被认为是有毒的。它是一种非金属，其性质介于硫族元素硫和碲之间。硒通过硒蛋白发挥其生物学功能。硒蛋白以第21位氨基酸--硒半胱氨酸(SEC)的形式含有硒，它是半胱氨酸的类似物，其含硫侧链被含硒侧链取代。SEC由UGA密码子编码，UGA密码子是非硒蛋白基因中用于mRNA翻译的三个终止密码子之一。要将UGA密码子识别为SEC插入位点而不是STOP，需要硒蛋白mRNAs中的SEC插入序列(SECIS)元件和独特的硒半胱基-tRNA，这两者都是由特定的蛋白质因子识别的。与20种标准氨基酸不同，SEC是由其tRNA上的丝氨酸生物合成的。人类基因组中编码了25种硒蛋白。大多数硒蛋白基因是通过生物信息学方法发现的，寻找框架内UGA密码子下游的SECIS元件。SEC被认为比半胱氨酸具有更强的亲核和亲电性质，并且SEC存在于所有硒酶的催化部位。大多数硒蛋白，其功能是已知的，参与氧化还原系统和信号通路。然而，一些硒蛋白在功能方面还没有得到很好的描述。在过去的几十年里，硒领域得到了极大的发展，有关硒生物学的研究正在为其对人类健康的重要性提供广泛的新信息。
Selenium is an essential micronutrient in mammals, but is also recognized as toxic in excess. It is a non-metal with properties that are intermediate between the chalcogen elements sulfur and tellurium. Selenium exerts its biological functions through selenoproteins. Selenoproteins contain selenium in the form of the 21st amino acid, selenocysteine (Sec), which is an analog of cysteine with the sulfur-containing side chain replaced by a Se-containing side chain. Sec is encoded by the codon UGA, which is one of three termination codons for mRNA translation in non-selenoprotein genes. Recognition of the UGA codon as a Sec insertion site instead of stop requires a Sec insertion sequence (SECIS) element in selenoprotein mRNAs and a unique selenocysteyl-tRNA, both of which are recognized by specialized protein factors. Unlike the 20 standard amino acids, Sec is biosynthesized from serine on its tRNA. Twenty-five selenoproteins are encoded in the human genome. Most of the selenoprotein genes were discovered by bioinformatics approaches, searching for SECIS elements downstream of in-frame UGA codons. Sec has been described as having stronger nucleophilic and electrophilic properties than cysteine, and Sec is present in the catalytic site of all selenoenzymes. Most selenoproteins, whose functions are known, are involved in redox systems and signaling pathways. However, several selenoproteins are not well characterized in terms of their function. The selenium field has grown dramatically in the last few decades, and research on selenium biology is providing extensive new information regarding its importance for human health.