by Merry Youle
For 50 years, researchers have mulled over why D. radiodurans is able to survive 100 times more ionizing radiation (IR) than other bacteria, 2000 times more than a human being. Although both DNA and proteins are damaged by IR, DNA was widely regarded as the critical target. That D. radiodurans can suffer 100 double strand DNA breaks per genome suggests an extraordinary DNA repair mechanism. Alas, such a mechanism has not been found.
Attention shifted in 2004 when Daly et al. reported that the most IR-resistant bacteria had 300 times more manganese and three times less iron than the most IR-sensitive ones.
Their recent study demonstrates that these minerals protect proteins, not DNA, from IR-induced oxidative damage. Lower the intracellular manganese content and the cells become sensitive to protein oxidation and radiation damage. The researchers postulated that manganese ions transform damaging superoxide radicals (which can't easily cross the cell membrane) into hydrogen peroxide, which can be excreted. Indeed, resistant cells excrete peroxide following radiation exposure.
The moral of this story? Protect your proteins and your DNA will take care of itself.