The heat shock protein ClpB mediates the development of thermotolerance in the cyanobacterium Synechococcus sp strain PCC 7942
The heat shock protein ClpB mediates the development of thermotolerance in the cyanobacterium Synechococcus sp strain PCC 7942
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DOI：
10.1128/jb.178.16.4839-4846.1996
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发表时间：
1996-08-01
影响因子：
3.2
通讯作者：
Clarke, AK
中科院分区：
文献类型：
--
作者：
Eriksson, MJ;Clarke, AK
热休克蛋白ClpB（HSP 100）是Clp多肽多样性组的成员，其作为分子伴侣和/或能量依赖性蛋白水解的调节剂起作用。从单细胞蓝细菌聚球藻属菌株PCC 7942中克隆并测序了编码ClpB同源物的单拷贝基因。预测的多肽序列与来自细菌和高等植物的胞质ClpB的序列最相似（即，70%至75%）。clpB在聚球藻属菌株PCC 7942中的失活导致在最佳生长条件下与野生型表型没有显著差异。在野生型中，两种形式的ClpB在从37到47.5或50摄氏度的温度变化期间被诱导，一种为92 kDa，与预测的大小相匹配，另一种为78 kDa的较小蛋白质。这两种蛋白质在Delta clpB菌株中均不存在。野生型中两种ClpB形式的诱导水平随着温度的升高而增加，而组成型ClpC蛋白的水平保持不变。然而，在Delta clpB菌株中，ClpC含量在加热期间几乎加倍，推测是为了补偿ClpB活性的损失。在47.5和50摄氏度的光合测量表明，无效突变体是没有更容易受到热灭活比野生型。以光合作用为代谢指标，建立了聚球藻的光合作用测定方法。以确定ClpB对于获得性耐热性的重要性。当温和型和Delta clpB菌株从37 ℃直接转移到55 ℃ 10分钟时，光合放氧完全失活。然而，通过将细胞在50 ℃预暴露1.5小时，在55 ℃处理10分钟后，野生型中保留了显著水平的光合作用，但突变体中没有。测定证实ClpB合成的损失导致聚球藻细胞发展耐热性的能力降低五倍。这些结果清楚地表明，在高温下诱导ClpB对于聚球藻属物种的持续耐热性至关重要，第一个这样的例子是光合生物或原核生物。
The heat shock protein ClpB (HSP100) is a member of the diverse group of Clp polypeptides that function as molecular chaperones and/or regulators of energy-dependent proteolysis. A single-copy gene coding for a ClpB homolog was cloned and sequenced from the unicellular cyanobacterium Synechococcus sp, strain PCC 7942. The predicted polypeptide sequence was most similar to sequences of cytosolic ClpB from bacteria and higher plants (i.e., 70 to 75%). Inactivation of clpB in Synechococcus sp, strain PCC 7942 resulted in no significant differences from the wild-type phenotype under optimal growth conditions. In the wild type, two forms of ClpB were induced during temperature shifts from 37 to 47.5 or 50 degrees C, one of 92 kDa, which matched the predicted size, and another smaller protein of 78 kDa. Both proteins were absent in the Delta clpB strain. The level of induction of the two ClpB forms in the wild type increased with increasingly higher temperatures, while the level of the constitutive ClpC protein remained unchanged. In the Delta clpB strain, however, the ClpC content almost doubled during the heating period, presumably to compensate for the loss of ClpB activity. Photosynthetic measurements at 47.5 and 50 degrees C showed that the null mutant was no more susceptible to thermal inactivation than the wild type. Using photosynthesis as a metabolic indicator, an assay was developed for Synechococcus spp. to determine the importance of ClpB for acquired thermotolerance. Complete inactivation of photosynthetic oxygen evolution occurred in both the mild type and the Delta clpB strain when they were shifted from 37 directly to 55 degrees C for 10 min. By preexposing the cells at 50 degrees C for 1.5 h, however, a significant level of photosynthesis was retained in the wild type but not in the mutant after the treatment at 55 degrees C for 10 min. Cell survival determinations confirmed that the loss of ClpB synthesis caused a fivefold reduction in the ability of Synechococcus cells to develop thermotolerance. These results clearly show that induction of ClpB at high temperatures is vital for sustained thermotolerance in Synechococcus spp., the first such example for either a photosynthetic or a prokaryotic organism.