von Janowsky Birgit, Major Tamara, Knapp Karin, Voos Wolfgang
Institut für Biochemie und Molekularbiologie, Hermann-Herder-Str. 7, Universität Freiburg, 79104 Freiburg, Germany.
J Mol Biol. 2006 Mar 31;357(3):793-807. doi: 10.1016/j.jmb.2006.01.008. Epub 2006 Jan 19.
Molecular chaperones are important components of mitochondrial protein biogenesis and are required to maintain the organellar function under normal and stress conditions. We addressed the functional role of the Hsp100/ClpB homolog Hsp78 during aggregation reactions and its functional cooperation with the main mitochondrial Hsp70, Ssc1, in mitochondria of the yeast Saccharomyces cerevisiae. By establishing an aggregation/disaggregation assay in intact mitochondria we demonstrated that Hsp78 is indispensable for the resolubilization of protein aggregates generated by heat stress under in vivo conditions. The ATP-dependent disaggregation activity of Hsp78 was capable of reversing the preprotein import defect of a destabilized mutant form of Ssc1. This role in disaggregation of Ssc1 is unique for Hsp78, since the recently identified, Hsp70-specific chaperone Zim17 had no effect on the resolubilization reaction. We observed only a minor effect of the second mitochondrial Hsp100 family member Mcx1 on protein disaggregation. A "holding" activity of the mitochondrial Hsp70 system was a prerequisite for a successful resolubilization of aggregated proteins. We conclude that the protective role of Hsp78 in thermotolerance is mainly based on maintaining the molecular chaperone Ssc1 in a soluble and functional state.
分子伴侣是线粒体蛋白质生物合成的重要组成部分，在正常和应激条件下维持细胞器功能是必需的。我们探讨了Hsp100/ClpB同源物Hsp78在聚集反应中的功能作用，以及它与酿酒酵母线粒体中主要的线粒体Hsp70即Ssc1的功能协作。通过在完整线粒体中建立聚集/解聚分析，我们证明Hsp78对于体内条件下热应激产生的蛋白质聚集体的再溶解是不可或缺的。Hsp78的ATP依赖性解聚活性能够逆转不稳定突变形式的Ssc1的前体蛋白导入缺陷。Hsp78在Ssc1解聚中的这一作用是独特的，因为最近鉴定出的Hsp70特异性伴侣蛋白Zim17对再溶解反应没有影响。我们仅观察到线粒体Hsp100家族的第二个成员Mcx1对蛋白质解聚有轻微影响。线粒体Hsp70系统的“保持”活性是聚集蛋白成功再溶解的先决条件。我们得出结论，Hsp78在耐热性中的保护作用主要基于将分子伴侣Ssc1维持在可溶且有功能的状态
