The mechanism of selenium incorporation into selenocysteine in humans.

描述（由申请人提供）：硒是唯一的遗传编码膳食微量营养素，对人类健康和生存至关重要。硒缺乏和硒蛋白基因的突变导致许多病理学，并且有强有力的证据表明硒在预防各种类型的癌症中是重要的。这些影响是显着的，当一个人认为硒是发现在只有两打的人类蛋白质。虽然硒发挥其生理作用的硒代半胱氨酸，只有少数的研究已旨在解释硒是如何纳入其主要代谢产物，并随后进入硒蛋白。此外，虽然在这个过程中的事件序列已经很好地描述了在原核生物模型系统的生化研究，很少有人知道在真核生物中，一般来说，在人类中，特别是相同的过程。在这里，重要的，但尚未探索的步骤，硒纳入硒半胱氨酸的机制将在人体系统进行研究。特别地，第一和末端合成反应的机制将在结构水平上确定。一系列代表硒代半胱氨酸形成不同阶段的二元和三元复合物将通过生物物理和生物化学方法进行研究。 硒代半胱氨酸在氨基酸中是独特的，不仅因为它含有必需的微量营养素，还因为它是在其tRNA上形成的。换句话说，虽然所有其他氨基酸都是独立于它们的tRNA形成的，但硒代半胱氨酸是在一系列反应中由氨基酸前体（丝氨酸）合成的，这些反应需要高度特异性的酶和硒代半胱氨酸tRNA。在第一个反应中，丝氨酰-tRNA合成酶（SerRS）“错误地”将丝氨酸与硒代半胱氨酸tRNA配对，而在第二个步骤中，硒代半胱氨酸-tRNA激酶（激酶）将丝氨酰磷酸化。在末端反应中，硒代半胱氨酸-tRNA合酶（合酶）在需要硒代磷酸盐的反应中促进磷酸丝氨酸转化为硒代半胱氨酸。硒磷酸盐是人体内连接硒代半胱氨酸合成和降解途径的主要硒供体。无论是与饲料摄入或提取硒蛋白降解硒首先转化为硒化物，然后转化为硒磷酸硒合酶2（SPS 2）。因此，SerRS活性可以调节初始反应底物的量，而合酶和SPS 2都可以调节硒插入氨基酸硒代半胱氨酸的效率。尽管硒代谢，在一般情况下，硒代半胱氨酸合成，特别是明显的重要性，很少有人知道如何人类SerRS，SPS 2和合成酶催化各自的反应，他们如何选择他们的反应底物和他们的活动是如何调节。在这里，这些机制将在结构水平上确定。拟议的研究将作为未来的研究在全细胞模型系统，其中临床相关的硒蛋白的合成的调节将被研究和新的治疗方法建立的潜力的基础。

DESCRIPTION (provided by applicant): Selenium, the only genetically encoded dietary micronutrient, is essential for human health and survival. Selenium deficiency and mutations in selenoprotein genes lead to numerous pathologies and there is strong evidence that selenium is important in preventing various types of cancer. These effects are remarkable when one considers that selenium is found in only two dozens of human proteins. Although selenium exerts its physiological role as selenocysteine, only a handful of studies have been aimed at explaining how selenium is incorporated into its major metabolite and subsequently into selenoproteins. Also, while the sequence of events during this process has been well described by biochemical studies in prokaryotic model systems, very little is known about the same process in eukaryotes, in general, and in humans, in particular. Here, important and yet unexplored steps in the mechanism of selenium incorporation into selenocysteine will be studied on the human system. In particular, the mechanisms of the first and terminal synthetic reactions will be determined at the structural level. A series of binary and ternary complexes that represent distinct stages in selenocysteine formation will be studied by biophysical and biochemical methods. Selenocysteine is unique amongst amino acids not only because it contains an essential micronutrient, but also because it is formed on its tRNA. In other words, while all other amino acids are formed independent of their tRNAs, selenocysteine is synthesized from an amino-acid precursor (serine) in a series of reactions that require highly specific enzymes and selenocysteine tRNA. In the first reaction, seryl-tRNA synthetase (SerRS) 'erroneously' pairs serine with selenocysteine tRNA, whereas in the second step, selenocysteine-tRNA kinase (kinase) phosphorylates the seryl group. In the terminal reaction, selenocysteine-tRNA synthase (synthase) promotes the conversion of phosphoserine into selenocysteine in a reaction that requires selenophosphate. Selenophosphate, in turn, is the main selenium donor in humans that links the synthetic and degradation pathways of selenocysteine. Selenium that is either ingested with fod or extracted from degraded selenoproteins is converted first into selenide and then into selenophosphate by a selenoenzyme selenophosphate synthase 2 (SPS2). Thus, SerRS activity may regulate the amount of the initial reaction substrate, whereas both synthase and SPS2 may regulate how efficiently selenium is inserted into the amino acid selenocysteine. Despite the obvious importance for selenium metabolism, in general, and selenocysteine synthesis, in particular, very little is known about how human SerRS, SPS2 and synthase catalyze respective reactions, how they select their reaction substrates and how their activities are regulated. Here, these mechanisms wil be determined at the structural level. The proposed study wil serve as a foundation for future studies in whole cell model systems in which the regulation of the synthesis of the clinically relevant selenoproteins will be studied and the potential for novel therapies established.