Park Yang-Nim, Zhao Xiaohong, Yim Yang-In, Todor Horia, Ellerbrock Robyn, Reidy Michael, Eisenberg Evan, Masison Daniel C, Greene Lois E
Laboratory of Cell Biology, NHLBI, NIH, Bethesda, Maryland, USA.
Eukaryot Cell. 2014 May;13(5):635-47. doi: 10.1128/EC.00300-13. Epub 2014 Mar 14.
The [PSI(+)] yeast prion is formed when Sup35 misfolds into amyloid aggregates. [PSI(+)], like other yeast prions, is dependent on the molecular chaperone Hsp104, which severs the prion seeds so that they pass on as the yeast cells divide. Surprisingly, however, overexpression of Hsp104 also cures [PSI(+)]. Several models have been proposed to explain this effect: inhibition of severing, asymmetric segregation of the seeds between mother and daughter cells, and dissolution of the prion seeds. First, we found that neither the kinetics of curing nor the heterogeneity in the distribution of the green fluorescent protein (GFP)-labeled Sup35 foci in partially cured yeast cells is compatible with Hsp104 overexpression curing [PSI(+)] by inhibiting severing. Second, we ruled out the asymmetric segregation model by showing that the extent of curing was essentially the same in mother and daughter cells and that the fluorescent foci did not distribute asymmetrically, but rather, there was marked loss of foci in both mother and daughter cells. These results suggest that Hsp104 overexpression cures [PSI(+)] by dissolution of the prion seeds in a two-step process. First, trimming of the prion seeds by Hsp104 reduces their size, and second, their amyloid core is eliminated, most likely by proteolysis.
当Sup35错误折叠成淀粉样聚集体时，就会形成[PSI(+)]酵母朊病毒。与其他酵母朊病毒一样，[PSI(+)]依赖于分子伴侣Hsp104，Hsp104会切断朊病毒种子，以便它们在酵母细胞分裂时传递下去。然而，令人惊讶的是，Hsp104的过表达也能治愈[PSI(+)]。已经提出了几种模型来解释这种效应：切断抑制、母细胞和子细胞之间种子的不对称分离以及朊病毒种子的溶解。首先，我们发现，无论是治愈的动力学，还是部分治愈的酵母细胞中绿色荧光蛋白（GFP）标记的Sup35病灶分布的异质性，都与Hsp104过表达通过抑制切断来治愈[PSI(+)]不相符。其次，我们排除了不对称分离模型，因为我们发现母细胞和子细胞中的治愈程度基本相同，荧光病灶并非不对称分布，而是母细胞和子细胞中的病灶都明显减少。这些结果表明，Hsp104过表达通过两步过程溶解朊病毒种子来治愈[PSI(+)]。首先，Hsp104对朊病毒种子的修剪会减小其大小，其次，其淀粉样核心很可能通过蛋白水解作用被消除。
