Move Over, DNA

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.

Two cells of D. ra­dio­du­rans  show­ing the dis­tri­b­u­tion of iron (red line) and man­ganese (turquoise, pur­ple, blue, and green lines in­di­cat­ing in­creas­ing con­cen­trations). Source

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.