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Query: UMLS:C1832526 (PCC)
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The heat shock protein CIpB (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 wild 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.
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PMID:The heat shock protein ClpB mediates the development of thermotolerance in the cyanobacterium Synechococcus sp. strain PCC 7942. 875 46

The heat shock protein ClpB is essential for acquired thermotolerance in cyanobacteria and eukaryotes and belongs to a diverse group of polypeptides which function as molecular chaperones. In this study we show that ClpB is also strongly induced during moderate cold stress in the unicellular cyanobacterium Synechococcus sp. strain PCC 7942. A fivefold increase in ClpB (92 kDa) content occurred when cells were acclimated to 25 degrees C over 24 h after being shifted from the optimal growth temperature of 37 degrees C. A corresponding increase occurred for the smaller ClpB' (78 kDa), which arises from a second translational start within the clpB gene of prokaryotes. Shifts to more extreme cold (i.e., 20 and 15 degrees C) progressively decreased the level of ClpB induction, presumably due to retardation of protein synthesis within this relatively cold-sensitive strain. Inactivation of clpB in Synechococcus sp. increased the extent of inhibition of photosynthesis upon the shift to 25 degrees C and markedly reduced the mutant's ability to acclimate to the new temperature regime, with a threefold drop in growth rate. Furthermore, around 30% fewer delta clpB cells survived the shift to 25 degrees C after 24 h compared to the wild type, and more of the mutant cells were also arrested during cell division at 25 degrees C, remaining attached after septum formation. Development of a cold thermotolerance assay based on cell survival clearly demonstrated that wild-type cells could acquire substantial resistance to the nonpermissive temperature of 15 degrees C by being pre-exposed to 25 degrees C. The same level of cold thermotolerance, however, occurred in the delta clpB strain, indicating ClpB induction is not necessary for this form of thermal resistance in Synechococcus spp. Overall, our results demonstrate that the induction of ClpB contributes significantly to the acclimation process of cyanobacteria to permissive low temperatures.
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PMID:Induction of the heat shock protein ClpB affects cold acclimation in the cyanobacterium Synechococcus sp. strain PCC 7942. 926 Sep 53