Tomala Katarzyna, Korona Ryszard
Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387, Krakow, Poland.
Mol Genet Genomics. 2008 Nov;280(5):409-17. doi: 10.1007/s00438-008-0374-x. Epub 2008 Sep 2.
Molecular chaperones recognize and bind destabilized proteins. This can be especially important for proteins whose stability is reduced by mutations. We focused our study on a major chaperone system, RAC-Ssb, which assists folding of newly synthesized polypeptides in the yeast cytosol. A sensitive phenotypic assay, the red color of Ade2 mutants, was used to screen for variants with metabolic activity dependent on RAC-Ssb. None of the Ade2 mutants were found to exhibit lower metabolic activity after inactivation of RAC-Ssb. In order to explicitly test the relationship between protein instability and activity of chaperones, a series of temperature sensitive Ade2 mutants were tested in the presence or absence of RAC-Ssb. The growth of Ade2(ts) mutants at elevated temperatures was enhanced if chaperones were missing. Similar pattern was found for thermally sensitive mutants of several other genes. Because RAC-Ssb normally supports the folding of proteins, it appears paradoxical that catabolic activity of mutants is reduced when these chaperones are present. We suggest that under non-stressful conditions, molecular chaperones are tuned to support folding of native proteins, but not that of mutated ones.
分子伴侣能够识别并结合不稳定的蛋白质。这对于那些因突变而稳定性降低的蛋白质来说尤为重要。我们的研究聚焦于一种主要的伴侣系统RAC-Ssb，它在酵母细胞质中协助新合成的多肽折叠。我们使用了一种灵敏的表型分析方法，即Ade2突变体的红色，来筛选代谢活性依赖于RAC-Ssb的变体。在RAC-Ssb失活后，未发现任何Ade2突变体表现出较低的代谢活性。为了明确测试蛋白质不稳定性与伴侣活性之间的关系，我们在有或没有RAC-Ssb的情况下测试了一系列温度敏感型Ade2突变体。如果缺少伴侣，Ade2（ts）突变体在高温下的生长会增强。其他几个基因的热敏感突变体也发现了类似的模式。由于RAC-Ssb通常支持蛋白质的折叠，所以当这些伴侣存在时突变体的分解代谢活性降低似乎是自相矛盾的。我们认为，在非应激条件下，分子伴侣被调整为支持天然蛋白质的折叠，而不是突变蛋白质的折叠。
