Ppra: an Important Protein of Radiation Resistance in Deinococcus Stimulates Catalase Activity in Escherichia Coli

Deinococcus radiodurans is characterized by its exceptional capacity to tolerate the effects of various DNA damaging agents due to presence of the extraordinary DNA repair mechanism. DNA double strand break repair in Deinococcus radiodurans follows biphasic kinetics. The phase I, a RecA independent phase appears to be a DNA protective and preparatory phase for RecA dependent phase II repair. PprA, an important protein of radiation tolerance in Deinococcus, was shown to stimulate both NAD and ATP dependent E. coli DNA ligase activity. Here we found another interesting role of PprA in stimulation of E. coli catalase activity. Transgenic E. coli cells expressing PprA from Deinococcus radiodurans showed an improved tolerance to hydrogen peroxide while the effect of ionizing and nonionizing radiation was similar to wild type. These cells showed nearly 3-fold higher catalase activity, which was mainly contributed by catalase E (KatE) and the levels of super-oxide dismutase were unchanged. The addition of purified PprA protein to cell free extract of non-recombinant E. coli cells has increased the catalase activity. But the PprA-antibody complex has no effect on the levels of catalase activity in-vitro. Furthermore, the addition of PprA antibodies to the cell free extract of PprA expressing E. coli cells has inhibited the catalase activity. The results suggest that free form of PprA per se stimulates the catalase activity in E. coli. This paper was awarded the Best Poster Prize at the “DAE-BRNS Life Sciences Symposium on Molecular Biology of Stress Response and its Applications”, held at BARC, Mumbai, during December 19-21, 2005.