Haslbeck Martin, Braun Nathalie, Stromer Thusnelda, Richter Bettina, Model Natascha, Weinkauf Sevil, Buchner Johannes
Institut für Organische Chemie und Biochemie, Technische Universität München, Garching, Germany.
EMBO J. 2004 Feb 11;23(3):638-49. doi: 10.1038/sj.emboj.7600080. Epub 2004 Jan 29.
Small heat shock proteins (sHsps) are ubiquitous molecular chaperones that prevent the unspecific aggregation of proteins. So far, Hsp26 was the only unambiguously identified member of the sHsp family in Saccharomyces cerevisiae. We show here that the sHsp system in the cytosol of S. cerevisiae consists of two proteins, Hsp26 and Hsp42. Hsp42 forms large dynamic oligomers with a barrel-like structure. In contrast to Hsp26, which functions predominantly at heat shock temperatures, Hsp42 is active as a chaperone under all conditions tested in vivo and in vitro. Under heat shock conditions, both Hsp42 and Hsp26 suppress the aggregation of one-third of the cytosolic proteins. This subset is about 90% overlapping for Hsp42 and Hsp26. The sHsp substrates belong to different biochemical pathways. This indicates a general protective function of sHsps for proteome stability in S. cerevisiae. Consistent with this observation, sHsp knockout strains show phenotypical defects. Taken together, our results define Hsp42 as an important player for protein homeostasis at physiological and under stress conditions.
小分子热休克蛋白（sHsps）是普遍存在的分子伴侣，可防止蛋白质发生非特异性聚集。到目前为止，Hsp26是酿酒酵母中唯一明确鉴定出的sHsp家族成员。我们在此表明，酿酒酵母胞质溶胶中的sHsp系统由两种蛋白质组成，即Hsp26和Hsp42。Hsp42形成具有桶状结构的大型动态寡聚体。与主要在热休克温度下起作用的Hsp26不同，Hsp42在体内和体外测试的所有条件下均作为伴侣蛋白具有活性。在热休克条件下，Hsp42和Hsp26均可抑制三分之一的胞质溶胶蛋白发生聚集。Hsp42和Hsp26的这一亚群约有90%重叠。sHsp的底物属于不同的生化途径。这表明sHsps对酿酒酵母蛋白质组稳定性具有普遍的保护作用。与这一观察结果一致，sHsp基因敲除菌株表现出表型缺陷。综上所述，我们的结果将Hsp42定义为生理条件和应激条件下蛋白质稳态的重要参与者。
