Hsp70 chaperones as modulators of prion life cycle:: Novel effects of Ssa and Ssb on the Sacharomyces cerevisiae prion [PSI+]
Hsp70 chaperones as modulators of prion life cycle:: Novel effects of Ssa and Ssb on the Sacharomyces cerevisiae prion [PSI+]
复制标题
DOI：
10.1534/genetics.104.037168
复制
发表时间：
2005-03-01
期刊：
影响因子：
3.3
通讯作者：
Chernoff, YO
中科院分区：
文献类型：
--
作者：
Allen, KD;Wegrzyn, RD;Chernoff, YO
[PSI+]是酵母释放因子Sup35的蛋白亚型。在一些检测中，Hsp70家族的胞质伴侣Ssa1和Ssb1/2分别表现出“亲[PSI+]”和“抗[PSI+]”效应。在这里，首次证明了过量的Ssa1增加了[PSI+]的从头形成，并且Ssa1的促[PSI+]效应被所有其他SSA蛋白所共享。嵌合结构的实验表明，多肽结合域是SSA和SSB蛋白对[PSI+]影响差异的主要决定因素。令人惊讶的是，当Sup35同时过度生产时，任何一种伴侣的过度生产都会增加[PSI+]的损失。过量的SSA会增加PrP聚合物的平均大小和单体Sup35蛋白的比例。体内和体外实验都揭示了Sup35和Hsp70蛋白之间的直接物理相互作用。所提出的模型假设SSA通过稳定错误折叠的蛋白质来刺激Pron的形成和聚合物的生长，这些蛋白质作为Pron转换的底物。在非常大的Prion聚集体的情况下，大小的进一步增加可能会导致Prion活性的丧失。相反，SSB要么刺激重新折叠成非Prion构象，要么以错误折叠的蛋白质为目标进行降解，以这种方式对抗Prion的形成和繁殖。
[PSI+] is a prion isoform of the yeast release factor Sup35. In some assays, the cytosolic chaperones Ssa1 and Ssb1/2 of the Hsp70 family were previously shown to exhibit "pro-[PSI+]" and "anti-[PSI+]" effects, respectively. Here, it is demonstrated for the first time that excess Ssa1 increases de novo formation of [PSI+] and that pro-[PSI+] effects of Ssa1 are shared by all other Ssa proteins. Experiments with chimeric constructs show that the peptide-binding domain is a major determinant of differences in the effects of Ssa and Ssb proteins on [PSI+]. Surprisingly, overproduction of either chaperone increases loss of [PSI+] when Sup35 is simultaneously overproduced. Excess Ssa increases both the average size of prion polymers and the proportion of monomeric Sup35 protein. Both in vivo and in vitro experiments uncover direct physical interactions between Sup35 and Hsp70 proteins. The proposed model postulates that Ssa stimulates prion formation and polymer growth by stabilizing misfolded proteins, which serve as substrates for prion conversion. In the case of very large prion aggregates, further increase in size may lead to the loss of prion activity. In contrast, Ssb either stimulates refolding into nonprion conformation or targets misfolded proteins for degradation, in this way counteracting prion formation and propagation.