Number of ClpP tetradecamers per cell during exponential phase

Range 250-300 Copies/cell
Organism Bacteria Escherichia coli
Reference Farrell CM, Grossman AD, Sauer RT. Cytoplasmic degradation of ssrA-tagged proteins. Mol Microbiol. 2005 Sep57(6):1750-61.PubMed ID16135238
Method Researchers sought to determine the intracellular levels of cytoplasmic proteases and adaptors known to be involved in degradation of ssrA-tagged substrates in vitro and to monitor how these levels might change with nutrient availability. For these studies, E. coli strain X90 was grown at 37°C in Neidhart’s complete medium (Neidhardt et al., 1974), a rich but de?ned broth, and samples were taken for analysis during exponential growth and early stationary phase. Quantitative Western blotting was used to measure the levels of ClpX, SspB, ClpA and ClpP. For each molecule, puri?ed protein at different concentrations was used to generate a standard curve. Comparison of the standard intensities with those of the cellular protein in the extract allowed calculation of the intracellular concentration. Intracellular levels of ClpS were determined by a competitive ELISA assay instead of Western blotting because the latter assay had high background caused by cross-reactivity.
Comments During exponential-phase growth, there was enough intracellular ClpA to form an average of 40–50 hexamers per cell (Fig. 1A). As cells entered early stationary phase, ClpA levels increased to a level of roughly 150 hexamers per cell (Fig. 1A). ClpP levels per cell also increased from an average of about 100 ClpP14 molecules during exponential-phase growth to 250–300 ClpP14 molecules as cells entered early stationary phase (Fig. 1A). In contrast, intracellular levels of ClpX and SspB changed far less, rising only about 20% throughout the experiment. On average, there was enough ClpX to form approximately 75–100 hexamers and enough SspB to form approximately 140–160 dimers per cell (Fig. 1B). ClpS levels also remained relatively constant at 250–300 molecules per cell throughout the experiment (Fig. 1B). Tetradecamer=An oligomer having fourteen subunits.
Entered by Uri M
ID 105106