Hesterkamp T, Bukau B
Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann Herder Strasse 7, D-79104 Freiburg, Germany.
EMBO J. 1998 Aug 17;17(16):4818-28. doi: 10.1093/emboj/17.16.4818.
Folding of newly synthesized cytosolic proteins has been proposed to require assistance by Hsp70 chaperones. We investigated whether two Hsp70 homologs of Escherichia coli, DnaK and HscA, have this role in vivo. Double mutants lacking dnaK and hscA were viable and lacked defects in protein folding at intermediate temperature. After heat shock, a subpopulation of pre-existing proteins slowly aggregated in mutants lacking DnaK, but not HscA, whereas the bulk of newly synthesized proteins displayed wild-type solubility. For thermolabile firefly luciferase, DnaK was dispensable for de novo folding at 30 degrees C, but essential for aggregation prevention during heat shock and subsequent refolding. DnaK and HscA are thus not strictly essential for folding of newly synthesized proteins. DnaK instead has functions in refolding of misfolded proteins that are essential under stress.
有人提出，新合成的胞质蛋白的折叠需要Hsp70伴侣蛋白的协助。我们研究了大肠杆菌的两个Hsp70同源物DnaK和HscA在体内是否具有这一作用。缺乏DnaK和HscA的双突变体是存活的，并且在中等温度下蛋白质折叠没有缺陷。热休克后，在缺乏DnaK而非HscA的突变体中，一部分预先存在的蛋白质会缓慢聚集，而大部分新合成的蛋白质表现出野生型溶解性。对于热不稳定的萤火虫荧光素酶，DnaK在30℃下对从头折叠不是必需的，但对于热休克期间防止聚集和随后的重折叠是必不可少的。因此，DnaK和HscA对于新合成蛋白质的折叠并非严格必需。相反，DnaK在错误折叠蛋白质的重折叠中具有在应激条件下至关重要的功能。
