Biology Department, Ursinus College, Collegeville, Pennsylvania, USA.
Department of Chemistry, University of California - Davis, Davis, California, USA.
Proteins. 2023 Jun;91(6):715-723. doi: 10.1002/prot.26461. Epub 2023 Jan 14.
Many human diseases are associated with the misfolding of amyloidogenic proteins. Understanding the mechanisms cells employ to ensure the integrity of the proteome is therefore a crucial step in the development of potential therapeutic interventions. Yeast cells possess numerous prion-forming proteins capable of adopting amyloid conformations, possibly as an epigenetic mechanism to cope with changing environmental conditions. The ribosome-associated complex (RAC), which docks near the ribosomal polypeptide exit tunnel and recruits the Hsp70 Ssb to chaperone nascent chains, can moderate the acquisition of these amyloid conformations in yeast. Here we examine the ability of the human RAC chaperone proteins Mpp11 and Hsp70L1 to function in place of their yeast RAC orthologues Zuo1 and Ssz1 in yeast lacking endogenous RAC and investigate the extent to which the human orthologues can perform RAC chaperone activities in yeast. We found that the Mpp11/Hsp70L1 complex can partially correct the growth defect seen in RAC-deficient yeast cells, although yeast/human hetero species complexes were variable in this ability. The proportion of cells in which the Sup35 protein undergoes spontaneous conversion to a [PSI ] prion conformation, which is increased in the absence of RAC, was reduced by the presence of the human RAC complex. However, the toxicity in yeast from expression of a pathogenically expanded polyQ protein was unable to be countered by the human RAC chaperones. This yeast system can serve as a facile model for studying the extent to which the human RAC chaperones contribute to combating cotranslational misfolding of other mammalian disease-associated proteins.
许多人类疾病都与淀粉样蛋白的错误折叠有关。因此，了解细胞用来确保蛋白质组完整性的机制是开发潜在治疗干预措施的关键步骤。酵母细胞具有许多能够形成淀粉样构象的朊病毒形成蛋白，这可能是一种表观遗传机制，以应对不断变化的环境条件。核糖体相关复合物（RAC），它停靠在核糖体多肽出口隧道附近，并招募 Hsp70 Ssb 来伴侣新生链，可以调节酵母中这些淀粉样构象的获得。在这里，我们研究了人类 RAC 伴侣蛋白 Mpp11 和 Hsp70L1 替代酵母 RAC 同源物 Zuo1 和 Ssz1 的能力，在缺乏内源性 RAC 的酵母中，以及研究人类同源物在酵母中执行 RAC 伴侣活性的程度。我们发现，Mpp11/Hsp70L1 复合物可以部分纠正 RAC 缺陷酵母细胞中观察到的生长缺陷，尽管酵母/人类杂种复合物在这种能力上存在差异。Sup35 蛋白自发转化为 [PSI ] 朊病毒构象的细胞比例在 RAC 缺失时增加，而人类 RAC 复合物的存在降低了这种比例。然而，表达致病性扩展多聚 Q 蛋白引起的酵母毒性不能被人类 RAC 伴侣抵消。这种酵母系统可以作为一个简单的模型，用于研究人类 RAC 伴侣在多大程度上有助于对抗其他与哺乳动物疾病相关的蛋白质的共翻译错误折叠。
