Formation and characterization of an all-ferrous Rieske cluster and stabilization of the [2Fe-2S]° core by protonation.

Autor: Leggate, Ellen J., Bill, Eckhard, Essigke, Timm, Ullmann, G. Matthias, Hirst, Judy
Předmět:
Zdroj: Proceedings of the National Academy of Sciences of the United States of America; 7/27/2004, Vol. 101 Issue 30, p10913-10918, 6p
Abstrakt: The all-ferrous Rieske cluster, [2Fe-2S]0, has been produced in solution and characterized by protein-film voltammetry and UV- visible, EPR, and Mössbauer spectroscopies. The [2Fe-2S]0 cluster, in the overexpressed soluble domain of the Rieske protein from the bovine cytochrome bc1 complex, is formed at -0.73 V at pH 7. Therefore, at pH 7, the [2Fe-2S]1+/0 couple is 1.0 V below the [2Fe-2S]2+/1+ couple. The two cluster-bound ferrous irons are both high spin (S = 2), and they are coupled antiferromagnetically (-J ≥ 30 cm-1, H = -2/S1.S2) to give a diamagnetic (S = 0) ground state. The ability of the Rieske cluster to exist in three oxidation states (2+, 1+, and 0) without an accompanying coupled reaction, such as a conformational change or protonation, is highly unusual. However, uncoupled reduction to the [2Fe-2S]0 state occurs at pH> 9.8 only, and at high pH the intact cluster persists in solution for <1 min. At pH <9.8, the all-ferrous cluster is stabilized significantly by protonation. A combination of experimental data and calculations based on density functional theory suggests strongly that the proton binds to one of the cluster μ2-sulfides, consistent with observations that reduced [3Fe-4S] clusters are protonated also. The implications for our understanding of coupled reactions at iron-sulfur clusters and of the factors that determine the relative stabilities of their different oxidation states are discussed. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index