Spectroscopic investigation of selective cluster conversion of archaeal zinc-containing ferredoxin from Sulfolobus sp strain 7

Archaeal zinc-containing ferredoxin from Sulfolobus sp. strain 7 contains o ne [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 similar to 6 iron atoms. The metal centers of this intermediate were analyzed by electron paramagne tic resonance (EPR), low temperature resonance Raman, x-ray absorption, and H-1 NMR spectroscopies. The spectroscopic data suggest that (i) cluster II was selectively converted to a cubane [3Fe-4S](1+) cluster in the intermed iate, without forming a stable radical species, and that (ii) the local met ric environments of cluster I and the isolated zinc site did not change sig nificantly in the intermediate. It is concluded that the initial step of ox idative 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 st ructural rearrangement of the protein does not occur. We propose a new sche me 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.