Mechanism of selenoprotein synthesis in bacteria

在细菌中，硒半胱氨酸的UGA终止密码子的消退需要一个特殊的翻译因子SELB、一个非规范的SEC-tRNASec和一个硒半胱氨酸掺入序列(SECIS)。本项目旨在了解硒半胱氨酸插入蛋白质的分子机制。将测量体内UGA重新编码的速率，并开发一种体外系统，允许硒半胱氨酸在体内快速和特异地掺入。将结合生物化学和生物物理技术研究三元络合物SELB-GTP-SEC-tRNASec与核糖体相互作用的动力学机制。本课程将讨论SELP对硒半胱氨酸插入过程中GTP的水解作用。SEC-tRNASec的积极校对将被调查，这可能是体内硒半胱氨酸掺入效率低的原因之一。在H.Stark和M.Wahl，MPI Göttingen的合作下，将分别用冷冻电子显微镜和结晶学研究功能性核糖体-SELB复合物和SELA-SEC-tRNASec复合物的结构。

In bacteria, the receding of a UGA stop codon for selenocysteine requires a specialized translation factor SelB, a non-canonical Sec-tRNASec, and a selenocysteine incorporation sequence (SECIS) in the mRNA. The present project aims at understanding the molecular mechanisms of selenocysteine insertion into proteins. The rate of UGA recoding in vivo will be measured and an in vitro system developed which allows selenocysteine incorporation at in vivo speed and specificity. Kinetic mechanisms of the interaction of the ternary complex SelB-GTP-Sec-tRNASec with the ribosome will be studied using a combination of biochemical and biophysical techniques. The role of GTP hydrolysis by SelB for selenocysteine insertion will be addressed. Aggressive proofreading of Sec-tRNASec, which is probably one reason for the low efficiency of in vivo selenocysteine incorporation, will be investigated. In collaboration with H. Stark and M. Wahl, MPI Göttingen, the structure of functional ribosome-SelB complexes and of the SelA-Sec-tRNASec complex will be studied by cryoelectron microscopy and crystallography, respectively.