High-resolution crystal structures of Desulfovibrio vulgaris (Hildenborough) nigerythrin: facile, redox-dependent iron movement, domain interface variability, and peroxidase activity in the rubrerythrins

High-resolution crystal structures of Desulfovibrio vulgaris nigerythrin (DvNgr), a member of the rubrerythrin (Rbr) family, demonstrate an approximately 2-Å movement of one iron (Fe1) of the diiron site from a carboxylate to a histidine ligand upon conversion of the mixed-valent (Fe2(II),Fe1(III)]) to diferrous states, even at cryogenic temperatures. This GluHis ligand toggling of one iron, which also occurs in DvRbr, thus, appears to be a characteristic feature of Rbr-type diiron sites. Unique features of DvNgr revealed by these structures include redox-induced flipping of a peptide carbonyl that reversibly forms a hydrogen bond to the histidine ligand to Fe1 of the diiron site, an intra-subunit proximal orientation of the rubredoxin-(Rub)-like and diiron domains, and an electron transfer pathway consisting of six covalent and two hydrogen bonds connecting the Rub-like iron with Fe2 of the diiron site. This pathway can account for DvNgrs relatively rapid peroxidase turnover. The characteristic combination of iron sites together with the redox-dependent iron toggling between protein ligands can account for the selectivity of Rbrs for hydrogen peroxide over dioxygen.Electronic Supplementary Material Supplementary material is available for this article at .An erratum to this article can be found at Ramesh B. Iyer and Radu Silaghi-Dumitrescu contributed equally to this work.