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The proteolytic activity of the HtrA (DegP) protein from Escherichia coli at low temperatures

University of Gdansk, Department of Biochemistry, Kadki 24, 80-822 Gdansk, Poland

Correspondence
Joanna Skorko-Glonek
glonek{at}biotech.ug.gda.pl

The HtrA (DegP) protein from Escherichia coli is a periplasmic protease whose function is to protect cells from the deleterious effects of various stress conditions. At temperatures below 28 °C the proteolytic activity of HtrA was regarded as negligible and it was believed that the protein mainly plays the role of a chaperone. In the present work we provide evidence that HtrA can in fact act as a protease at low temperatures. Under folding stress, caused by disturbances in the disulfide bond formation, the lack of proteolytic activity of HtrA lowered the survival rates of mutant strains deprived of a functional DsbA/DsbB oxidoreductase system. HtrA degraded efficiently the unfolded, reduced alkaline phosphatase at 20 °C, both in vivo and in vitro. The cleavage was most efficient in the case of HtrA deprived of its internal S–S bond; therefore we expect that the reduction of HtrA may play a regulatory role in proteolysis.