Chapter 5 - Low-molecular dinitrosyl iron complexes can catalyze the degradation of active centers of iron-sulfur proteins

Abstract

Many recent studies have shown that iron—sulfur proteins (ISPs) are targets for endogenous nitric oxide (NO) radicals. The action of NO on the iron—sulfur centers (ISCs) of ISP has been recognized as one of the signaling pathways of NO in cells and tissues. The interaction leads to the deactivation of ISPs due to degradation of the ISCs. The degradation is often concomitant with the formation of paramagnetic dinitrosyl iron complexes (DNICs) with thiolate ligands. These complexes have the generic structure {(RS−)2Fe+(NO+)2}+, where the unpaired electrons of the nitrosyl ligands are largely transferred to the iron atom. The complexes are paramagnetic and their EPR absorption near gav = 2.03 is often considered as a marker of NO-mediated degradation of the ISCs. The ISPs are usually classified according to the number of iron atoms in the ISC clusters: one, two, three, or four, respectively. In most of these proteins, the iron atoms are held by sulfur atoms of cysteine side chains, with a few exceptions having coordination of nitrogen atoms from histidines. In polynuclear clusters, the iron atoms are held together by additional sulfide ions. A possible mechanism of disruption of a reduced binuclear [Fe2S2] cluster by NO proceeds by ligand replacement, where the inorganic sulfur atoms (S*) are replaced by NO moieties.