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Translocon-Associated Protein Complex (TRAP) is Crucial for Co-Translational Translocation of Pre-Proinsulin
Journal of Molecular Biology ( IF 5.6 ) Pub Date : 2020-10-31 , DOI: 10.1016/j.jmb.2020.10.028
T. Kriegler , G. Kiburg , T. Hessa

Many unanswered questions remain in understanding the biosynthesis of the peptide hormone insulin. Here we elucidate new aspects in the mechanism of co-translational translocation initiation of pre-proinsulin in the endoplasmic reticulum. We utilize a translational arrest peptide derived from the x-box-binding protein (Xbp1) to induce ribosomal stalling and generate translocation intermediates. We find that the insulin signal sequence is rather weakly gating and requires the assistance of auxiliary translocon components to initiate translocation. Probing the translational intermediates with chemical crosslinking, we identified an early interaction with the translocon-associated protein (TRAP) complex. The TRAPβ subunit interacts with pre-proinsulin before the peptide enters the Sec61 translocon channel in a signal sequence-dependent manner. We describe the substrate sequence determinants that are recognized by TRAP on the cytosolic site of the membrane to facilitate substrate-specific opening of the Sec61 translocon channel. Our findings support the hypothesis that the TRAP-dependence is in part determined by the content of glycine and proline residues mainly within the signal sequence.



中文翻译:

Translocon相关蛋白复合物(TRAP)对于前胰岛素原的共翻译转运至关重要

在理解肽激素胰岛素的生物合成方面,还有许多未解决的问题。在这里,我们阐明内质网中前胰岛素原的共翻译易位启动机制的新方面。我们利用源自x盒结合蛋白(Xbp1)的翻译逮捕肽来诱导核糖体停转并生成易位中间体。我们发现,胰岛素信号序列的门控作用较弱,需要辅助转运子成分的协助才能启动转运。探索与化学交联的翻译中间体,我们确定了与translocon相关蛋白(TRAP)复杂的早期互动。在肽以信号序列依赖性方式进入Sec61转运子通道之前,TRAPβ亚基与胰岛素原前体相互作用。我们描述了在膜的胞质位点上被TRAP识别的底物序列决定簇,以促进Sec61 translocon通道的底物特异性开放。我们的发现支持以下假设:TRAP依赖性部分取决于主要在信号序列内的甘氨酸和脯氨酸残基的含量。

更新日期:2020-12-02
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