Hottiger T, De Virgilio C, Bell W, Boller T, Wiemken A
Botanisches Institut, Universität Basel, Switzerland.
Eur J Biochem. 1992 Nov 15;210(1):125-32. doi: 10.1111/j.1432-1033.1992.tb17399.x.
In the yeast, Saccharomyces cerevisiae, the disaccharide trehalose is a stress-related metabolite that accumulates upon exposure of cells to heat shock or a variety of non-heat inducers of the stress response. Here, we describe the influence of mutations in individual heat-shock-protein genes on trehalose metabolism. A strain mutated in three proteins of the SSA subfamily of 70-kDa heat-shock proteins (hsp70) overproduced trehalose during heat shock at 37 degrees C or 40 degrees C and showed abnormally slow degradation of trehalose upon temperature decrease from 40 degrees C to 27 degrees C. The mutant cells were unimpaired in the induction of thermotolerance; however, the decay of thermotolerance during recovery at 27 degrees C was abnormally slow. Since both a high content of trehalose and induced thermotolerance are associated with the heat-stressed state of cells, the abnormally slow decline of trehalose levels and thermotolerance in the mutant cells indicated a defect in recovery from the heat-stressed state. A similar albeit minor defect, as judged from measurements of trehalose degradation during recovery, was detected in a delta hsp104 mutant, but not in a strain deleted in the polyubiquitin gene, UB14. In all our experiments, trehalose levels were closely correlated with thermotolerance, suggesting a thermoprotective function of trehalose. In contrast, heat-shock proteins, in particular hsp70, appear to be involved in recovery from the heat-stressed state rather than in the acquisition of thermotolerance. Cells partially depleted of hsp70 displayed an abnormally low activity of neutral trehalase when shifted to 27 degrees C after heat shock at 40 degrees C. Trehalase activity is known to be under positive control by cAMP-dependent protein kinases, suggesting that hsp70 directly or indirectly stimulate these protein-kinase activities. Alternatively, hsp70 may physically interact with neutral trehalase, thereby protecting the enzyme from thermal denaturation.
在酿酒酵母中，二糖海藻糖是一种与应激相关的代谢产物，当细胞受到热休克或多种应激反应的非热诱导剂作用时会积累。在此，我们描述了单个热休克蛋白基因突变对海藻糖代谢的影响。一个在70 kDa热休克蛋白（hsp70）的SSA亚家族的三种蛋白质中发生突变的菌株，在37℃或40℃热休克期间过量产生海藻糖，并且在温度从40℃降至27℃时，海藻糖的降解异常缓慢。突变细胞在耐热性诱导方面未受损；然而，在27℃恢复期间耐热性的衰减异常缓慢。由于高含量的海藻糖和诱导的耐热性都与细胞的热应激状态相关，突变细胞中海藻糖水平和耐热性异常缓慢的下降表明从热应激状态恢复存在缺陷。从恢复期间海藻糖降解的测量判断，在Δhsp104突变体中检测到类似但较小的缺陷，但在多聚泛素基因UB14缺失的菌株中未检测到。在我们所有的实验中，海藻糖水平与耐热性密切相关，表明海藻糖具有热保护功能。相比之下，热休克蛋白，特别是hsp70，似乎参与从热应激状态的恢复，而不是耐热性的获得。在40℃热休克后转移到27℃时，hsp70部分缺失的细胞显示中性海藻糖酶活性异常低。已知海藻糖酶活性受cAMP依赖性蛋白激酶的正调控，这表明hsp70直接或间接刺激这些蛋白激酶活性。或者，hsp70可能与中性海藻糖酶发生物理相互作用，从而保护该酶免受热变性。
