Xia B, Ke H, Inouye M
Department of Biochemistry, UMDNJ-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
Mol Microbiol. 2001 Apr;40(1):179-88. doi: 10.1046/j.1365-2958.2001.02372.x.
Escherichia coli contains a large CspA family, CspA to CspI. Here, we demonstrate that E. coli is highly protected against cold-shock stress, as these CspA homologues existed at approximately a total of two million molecules per cell at low temperature and growth defect was not observed until four csp genes (cspA, cspB, cspE and cspG) were deleted. The quadruple-deletion strain acquired cold sensitivity and formed filamentous cells at 15 degrees C although chromosomes were normally segregated. The cold-sensitivity and filamentation phenotypes were suppressed by all members of the CspA family except for CspD, which causes lethality upon overexpression. Interestingly, the cold sensitivity of the mutant was also suppressed by the S1 domain of polynucleotide phosphorylase (PNPase), which also folds into a beta-barrel structure similar to that of CspA. The present results show that cold-shock proteins and S1 domains share not only the tertiary structural similarity but also common functional properties, suggesting that these seemingly distinct protein categories may have evolved from a common primordial RNA-binding protein.
大肠杆菌含有一个庞大的CspA家族，从CspA到CspI。在此，我们证明大肠杆菌对冷休克胁迫具有高度抗性，因为这些CspA同源物在低温下每个细胞中大约总共存在两百万个分子，并且直到四个csp基因（cspA、cspB、cspE和cspG）被缺失才观察到生长缺陷。四缺失菌株获得了冷敏感性，并且在15摄氏度时形成丝状细胞，尽管染色体正常分离。除了CspD（过表达时会导致致死性）之外，CspA家族的所有成员都抑制了冷敏感性和丝状化表型。有趣的是，多核苷酸磷酸化酶（PNPase）的S1结构域也抑制了突变体的冷敏感性，该结构域也折叠成与CspA类似的β桶结构。目前的结果表明，冷休克蛋白和S1结构域不仅具有三级结构相似性，而且具有共同的功能特性，这表明这些看似不同的蛋白质类别可能是从一个共同的原始RNA结合蛋白进化而来的。
