Frees D, Ingmer H
Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Frederiksberg, Denmark.
Mol Microbiol. 1999 Jan;31(1):79-87. doi: 10.1046/j.1365-2958.1999.01149.x.
ClpP proteins constitute a family of homologous proteins found in both prokaryotic and eukaryotic organisms. In Escherichia coli, ClpP is the proteolytic component of a large complex also containing either the ClpA or the ClpX ATPases. We show here that the clpP gene from the Gram-positive bacterium Lactococcus lactis encodes a 22-kDa protein that is induced by low pH and by the t-RNA analogue puromycin, which interferes with translation, resulting in the production of misfolded puromycyl-containing peptides. Northern blot and primer extension analysis showed that clpP expression is also induced by heat shock and that stress induction occurs at the transcriptional level independent of the CIRCE regulatory element often implicated in stress regulation in Gram-positive bacteria. When we disrupted the L. lactis clpP gene by insertional inactivation, the resulting mutant was more sensitive to both heat and puromycin than wild-type cells. Furthermore, cells lacking ClpP had a reduced ability to degrade puromycyl-containing peptides, and they synthesized heat shock proteins constitutively in the absence of stress. Thus, our data suggest that ClpP plays a major role in the degradation of misfolded proteins.
ClpP蛋白构成了一类在原核生物和真核生物中均能找到的同源蛋白家族。在大肠杆菌中，ClpP是一个大型复合物的蛋白水解成分，该复合物还包含ClpA或ClpX ATP酶。我们在此表明，革兰氏阳性细菌乳酸乳球菌的clpP基因编码一种22 kDa的蛋白，该蛋白可被低pH值以及干扰翻译的tRNA类似物嘌呤霉素诱导产生，从而导致含错误折叠的嘌呤霉素化肽段的生成。Northern印迹和引物延伸分析表明，clpP的表达也受热激诱导，且应激诱导发生在转录水平，不依赖于革兰氏阳性细菌应激调节中常涉及的CIRCE调控元件。当我们通过插入失活破坏乳酸乳球菌的clpP基因时，所得突变体比野生型细胞对热和嘌呤霉素都更敏感。此外，缺乏ClpP的细胞降解含嘌呤霉素化肽段的能力降低，并且它们在无应激条件下组成性地合成热休克蛋白。因此，我们的数据表明ClpP在错误折叠蛋白的降解中起主要作用。
