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 t he peptidase ClpP in the cell is crucial for tolerance of many forms of str ess in Bacillus subtilis. Assays for detection of defects in protein degrad ation suggest that ClpC, ClpP, and ClpX participate directly in overall pro teolysis of misfolded proteins. Turnover rates for abnormal puromycyl pepti des are significantly decreased in clpC, clpP, and clpX mutant cells. Elect ron-dense aggregates, most likely due to the accumulation of misfolded prot eins, were noticed in studies of ultrathin cryosections in clpC and clpP mu tant cells even under nonstress conditions. In contrast, in the wild type o r clpX mutants such aggregates could only be observed after heat shock. Thi s phenomenon supports the assumption that clpC and clpP mutants are deficie nt in the ability to solubilize or degrade damaged and aggregated proteins, the accumulation of which is toxic for the cell. By using immunogold label ing with antibodies raised against ClpC, ClpP, and ClpX, the Clp proteins w ere localized in these aggregates,showing that the Clp proteins act at this level in vivo.