Reversible inactivation of E. coli endonuclease III via modification of its [4Fe-4S] cluster by nitric oxide

Endonuclease III, a highly conserved enzyme initiating the base excision repair of oxidized DNA bases, hosts a 4Fe-4S] cluster. Unlike many other iron-sulfur clusters, the 4Fe-4S] cluster of endonuclease III is stable and resistant to both oxidation and reduction. Here we show that the 4Fe-4S] cluster of the E. coli endonuclease III can be readily modified by nitric oxide forming the protein-bound dinitrosyl iron complex in vitro and in vivo. Modification of the 4Fe-4S] cluster completely inhibits the DNA glycosylase activity of the endonuclease III. Remarkably, the enzymatic activity is restored when the 4Fe-4S] cluster is re-assembled in the endonuclease III dinitrosyl iron complex with L-cysteine, cysteine desulfurase (IscS) and ferrous iron in vitro. Furthermore, the nitric oxide-modified 4Fe-4S] cluster in endonuclease III is efficiently repaired in aerobically growing E. coli cells, and this repair does not require new protein synthesis. These results suggest that the E. coli endonuclease III can be reversibly inactivated by nitric oxide via modification of its 4Fe-4S] cluster.