Translocation of proteins across biological membranes is essential for life. Proteins that clog the endoplasmic reticulum (ER) translocon prevent the movement of other proteins into the ER. Eukaryotes have multiple translocon quality control (TQC) mechanisms to detect and destroy proteins that persistently engage the translocon. TQC mechanisms have been defined using a limited panel of substrates that aberrantly occupy the channel. The extent of substrate overlap among TQC pathways is unknown. In this study, we found that two TQC enzymes, the ER-associated degradation ubiquitin ligase Hrd1 and zinc metalloprotease Ste24, promote degradation of characterized translocon-associated substrates of the other enzyme in Saccharomyces cerevisiae. Although both enzymes contribute to substrate turnover, our results suggest a prominent role for Hrd1 in TQC. Yeast lacking both Hrd1 and Ste24 exhibit a profound growth defect, consistent with overlapping function. Remarkably, two mutations that mildly perturb post-translational translocation and reduce the extent of aberrant translocon engagement by a model substrate diminish cellular dependence on TQC enzymes. Our data reveal previously unappreciated mechanistic complexity in TQC substrate detection and suggest that a robust translocon surveillance infrastructure maintains functional and efficient translocation machinery.

中文翻译：

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Hrd1 和 Ste24 在 translocon 质量控制中的重叠功能提供了强大的通道监控

蛋白质跨生物膜的易位对生命至关重要。堵塞内质网 (ER) 转位子的蛋白质会阻止其他蛋白质进入内质网。真核生物具有多种易位子质量控制 (TQC) 机制来检测和破坏持续参与易位子的蛋白质。TQC 机制已被定义为使用异常占据通道的有限基板面板。TQC 通路之间底物重叠的程度是未知的。在这项研究中，我们发现两种 TQC 酶，ER 相关降解泛素连接酶 Hrd1 和锌金属蛋白酶 Ste24，可促进酿酒酵母中另一种酶的特征转位子相关底物的降解。尽管这两种酶都有助于底物周转，但我们的结果表明 Hrd1 在 TQC 中起重要作用。缺乏 Hrd1 和 Ste24 的酵母表现出严重的生长缺陷，与重叠功能一致。值得注意的是，两个突变轻微扰乱了翻译后易位并减少了模型底物引起的异常转位子参与的程度，减少了细胞对 TQC 酶的依赖。我们的数据揭示了 TQC 底物检测中以前未被重视的机械复杂性，并表明强大的易位监测基础设施可以保持功能性和高效的易位机械。