Spectroscopic investigation of selective cluster conversion of archaeal zinc-containing ferredoxin from Sulfolobus sp. strain 7 |
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Authors: | Iwasaki T Watanabe E Ohmori D Imai T Urushiyama A Akiyama M Hayashi-Iwasaki Y Cosper N J Scott R A |
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Institution: | Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo, Japan. iwasaki/biochem@om.nms.ac.jp |
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Abstract: | Archaeal zinc-containing ferredoxin from Sulfolobus sp. strain 7 contains one 3Fe-4S] cluster (cluster I), one 4Fe-4S] cluster (cluster II), and one isolated zinc center. Oxidative degradation of this ferredoxin led to the formation of a stable intermediate with 1 zinc and approximately 6 iron atoms. The metal centers of this intermediate were analyzed by electron paramagnetic resonance (EPR), low temperature resonance Raman, x-ray absorption, and (1)H NMR spectroscopies. The spectroscopic data suggest that (i) cluster II was selectively converted to a cubane 3Fe-4S](1+) cluster in the intermediate, without forming a stable radical species, and that (ii) the local metric environments of cluster I and the isolated zinc site did not change significantly in the intermediate. It is concluded that the initial step of oxidative degradation of the archaeal zinc-containing ferredoxin is selective conversion of cluster II, generating a novel intermediate containing two 3Fe-4S] clusters and an isolated zinc center. At this stage, significant structural rearrangement of the protein does not occur. We propose a new scheme for oxidative degradation of dicluster ferredoxins in which each cluster converts in a stepwise manner, prior to apoprotein formation, and discuss its structural and evolutionary implications. |
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