Department of Biology and BioX Program, Stanford University, Stanford, California, United States of America.
PLoS Biol. 2011 Jul;9(7):e1001100. doi: 10.1371/journal.pbio.1001100. Epub 2011 Jul 12.
Polypeptides exiting the ribosome must fold and assemble in the crowded environment of the cell. Chaperones and other protein homeostasis factors interact with newly translated polypeptides to facilitate their folding and correct localization. Despite the extensive efforts, little is known about the specificity of the chaperones and other factors that bind nascent polypeptides. To address this question we present an approach that systematically identifies cotranslational chaperone substrates through the mRNAs associated with ribosome-nascent chain-chaperone complexes. We here focused on two Saccharomyces cerevisiae chaperones: the Signal Recognition Particle (SRP), which acts cotranslationally to target proteins to the ER, and the Nascent chain Associated Complex (NAC), whose function has been elusive. Our results provide new insights into SRP selectivity and reveal that NAC is a general cotranslational chaperone. We found surprising differential substrate specificity for the three subunits of NAC, which appear to recognize distinct features within nascent chains. Our results also revealed a partial overlap between the sets of nascent polypeptides that interact with NAC and SRP, respectively, and showed that NAC modulates SRP specificity and fidelity in vivo. These findings give us new insight into the dynamic interplay of chaperones acting on nascent chains. The strategy we used should be generally applicable to mapping the specificity, interplay, and dynamics of the cotranslational protein homeostasis network.
多肽从核糖体中释放出来后，必须在细胞拥挤的环境中折叠和组装。伴侣蛋白和其他蛋白质稳态因子与新翻译的多肽相互作用，促进其折叠和正确定位。尽管已经进行了广泛的研究，但对于与新生多肽结合的伴侣蛋白和其他因子的特异性知之甚少。为了解决这个问题，我们提出了一种通过与核糖体-新生链-伴侣复合物相关的 mRNA 系统地鉴定共翻译伴侣底物的方法。我们在这里重点关注两种酿酒酵母伴侣蛋白：信号识别颗粒 (SRP)，它在共翻译过程中靶向蛋白质到内质网，以及新生链相关复合物 (NAC)，其功能尚不清楚。我们的结果为 SRP 的选择性提供了新的见解，并揭示了 NAC 是一种通用的共翻译伴侣。我们发现 NAC 的三个亚基具有令人惊讶的差异底物特异性，它们似乎识别新生链中的不同特征。我们的结果还揭示了与 NAC 和 SRP 分别相互作用的新生多肽集合之间存在部分重叠，并表明 NAC 在体内调节 SRP 的特异性和保真度。这些发现使我们对作用于新生链的伴侣蛋白的动态相互作用有了新的认识。我们使用的策略应该可以普遍应用于绘制共翻译蛋白质稳态网络的特异性、相互作用和动态图谱。
