T. Iwasaki et al., Spectroscopic investigation of selective cluster conversion of archaeal zinc-containing ferredoxin from Sulfolobus sp strain 7, J BIOL CHEM, 275(33), 2000, pp. 25391-25401
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.