DegP acts as a chaperone at low temperatures but switches to a peptidase (heat shock protein) at higher temperatures (PubMed:10319814). Degrades transiently denatured and unfolded or misfolded proteins which accumulate in the periplasm following heat shock or other stress conditions (PubMed:16303867). DegP is efficient with Val-Xaa and Ile-Xaa peptide bonds, suggesting a preference for beta-branched side chain amino acids (PubMed:8830688). Only unfolded proteins devoid of disulfide bonds appear capable of being cleaved, thereby preventing non-specific proteolysis of folded proteins (PubMed:8830688). Its proteolytic activity is essential for the survival of cells at elevated temperatures (PubMed:7557477). It can degrade IciA, Ada, casein, globin and PapA. DegP shares specificity with DegQ (PubMed:8830688). DegP is also involved in the biogenesis of partially folded outer-membrane proteins (OMP). Acts on substrates that are at least partially unfolded. The cleavage site P1 residue is normally between a pair of hydrophobic residues, such as Val-|-Val. Inhibited by diisopropylfluorophosphate (DFP). Optimum temperature is around 55 degrees Celsius. In the range from 37 to 55 degrees Celsius, the proteolytic activity rapidly increases with temperature. DegP can reversibly switch between different oligomeric forms that represent inactive (6-mer) and active (12- and 24-mer) protease states. Substrate binding triggers the conversion of the resting DegP trimer and hexamer into catalytically active 12- and 24-mers. The conversion of 6-mer (DegP6) into 12-mer (DegP12) or 24-mer (DegP24) is crucial in regulating protease activity. By heat shock (PubMed:3057437). Transcriptionally up-regulated by sigma-E factor and the Cpx two-component signal transduction pathway (PubMed:7883164, PubMed:9351822). Decreased induction of Cpx two-component regulatory system (PubMed:16166523). Increased accumulation of periplasmic accessory protein CpxP, increased accumulation and toxicity of overexpressed, misfolded periplasmic proteins (PubMed:16303867). Increased resistance to hydroxyurea, probably due to decreased degradation of misfolded proteins which eventually leads to decreased OH radical formation (PubMed:20005847). DegP is indispensable for bacterial survival at temperatures above 42 degrees Celsius, however is also able to digest its natural substrates in a reducing environment at temperatures as low as 20 degrees Celsius. Belongs to the peptidase S1C family.