The clp proteases of Bacillus subtilis are directly involved in degradation of misfolded proteins.
The presence of the heat stress response-related ATPases ClpC and ClpX or the peptidase ClpP in the cell is crucial for tolerance of many forms of stress in Bacillus subtilis. Assays for detection of defects in protein degradation suggest that ClpC, ClpP, and ClpX participate directly in overall proteolysis of misfolded proteins. Turnover rates for abnormal puromycyl peptides are significantly decreased in clpC, clpP, and clpX mutant cells. Electron-dense aggregates, most likely due to the accumulation of misfolded proteins, were noticed in studies of ultrathin cryosections in clpC and clpP mutant cells even under nonstress conditions. In contrast, in the wild type or clpX mutants such aggregates could only be observed after heat shock. This phenomenon supports the assumption that clpC and clpP mutants are deficient in the ability to solubilize or degrade damaged and aggregated proteins, the accumulation of which is toxic for the cell. By using immunogold labeling with antibodies raised against ClpC, ClpP, and ClpX, the Clp proteins were localized in these aggregates, showing that the Clp proteins act at this level in vivo.
Krüger
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E
Institut für Mikrobiologie und Molekularbiologie, Ernst-Moritz-Arndt-Universität Greifswald, D-17487 Greifswald, Germany.
Witt
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E
Ohlmeier
S
S
Hanschke
R
R
Hecker
M
M
D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001412:Bacillus subtilis / Q000201:enzymology* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D002451:Cell Compartmentation; D049071:Endopeptidase Clp; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D018832:Molecular Chaperones; D009154:Mutation; D011489:Protein Denaturation; D017510:Protein Folding; D012697:Serine Endopeptidases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
D001426:Bacterial Proteins; C087481:ClpC protein, Bacteria; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D012697:Serine Endopeptidases; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases; C088072:ClpX protein, E coli; D000074183:ATPases Associated with Diverse Cellular Activities