Evidence for N coordination to Fe in the [2Fe‐2S] center in yeast mitochondrial complex III Comparison with similar findings for analogous bacterial [2Fe‐2S] proteins

Abstract

Yeast mitochondrial complex III contains a subunit with a [2Fe-2S] cluster (the Rieske center) that has unusual physical and chemical properties. For apparently similar centers isolated from bacteria, it has been shown by electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) measurements that these [2Fe-2S] centers are coordinated by at least one and probably two nitrogen ligands. This work describes similar ENDOR and ESEEM studies on the intact mitochondrial complex. We find that this [2Fe-2S] cluster exhibits ESEEM and ENDOR properties that appear to be indistinguishable from those observed with the isolated bacterial systems. Furthermore, changes in EPR lineshape that occur as complex III is progressively reduced are not accompanied by any changes in the nitrogen coupling parameters. This spectroscopic evidence for nitrogen coordination is supported by published sequence data on four Rieske iron-sulfur subunits. It seems likely that this is a general characteristic of such [2Fe-2S] redox active centers.

Characterization and Crystallization of the Lumen Side Domain of the Chloroplast Rieske Iron-Sulfur Protein

“…1) and a unique amino-terminal sequence (NH 2 -Phe-Val-Pro-Pro-Gly-Gly) obtained of the fragment (Table I). The latter sequence is identical to that of residues [41][42][43][44][45][46] of the Rieske protein from spinach chloroplasts (17). The similarity of the purification procedures used to isolate the Rieske protein fragment from the bc 1 and b 6 f complexes is somewhat surprising, considering: (i) the subunit composition of the bc 1 and b 6 f complexes, and the amino acid sequences of the other subunits, cytochromes f and c 1 , which also have a large peripheral domain that could be solubilized by proteases, are very different (4,18); (ii) only nine of the first 65 residues of the soluble chloroplast Rieske protein fragment are identical to the mitochondrial Rieske fragment (19) ( Table I).…”

“…Although the E m values of the soluble chloroplast Rieske protein stated above are quite similar to those measured by EPR (40), depending on whether or not a temperature correction to the E m is made, the E m6 are 50 -70 mV more positive (approximately ϩ350 -365 mV versus ϩ295 mV) than those measured for the Rieske protein in the b 6 f complex. Therefore, because the Ϫ1 net charge of the reduced iron-sulfur cluster is greater than that of the electrically neutral oxidized cluster (43), it appears that the environment of the cluster in the soluble Rieske protein is somewhat more polar than for the Rieske cluster embedded in the b 6 f complex.…”

Nickel hydrogenases: in search of the active site

“…To ascribe the remaining two cysteines as ligands for an Fe-S cluster is rather unlikely. It is not impossible, though, as some [2Fe-2S] clusters are proposed to have up to two non-sulphur ligands [67,85,201].…”

Isolation, Characterisation and Crystallisation of a Water‐Soluble Fragment of the Rieske Iron‐Sulfur Protein of Bovine Heart Mitochondrial bc1 Complex

“…From electron nuclear double resoCorrespondence ro T. A. Link, Universitatsklinikum Frankfurt, ZBC, Therapeutische Biochemie, Theodor-Stern-Kai 7, Haus 25B, D-60590 Frankfumain, Germany nance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopy there is good evidence that Rieske type [2Fe-2S] clusters, which are also present in bacterial dioxygenases, have two histidine residues coordinated to the Fe(II), in contrast to the four-cysteine ligation pattern of the ferredoxins (Cline at al., 1985;Telser et al, 1987;Gurbiel et a]., 1989Gurbiel et a]., , 1991Britt et al, 1991).…”