Desulforedoxin (Dx), isolated from the sulfate
reducing bacterium Desulfovibrio gigas, is a small
homodimeric (2 × 36 amino acids) protein. Each subunit
contains a high-spin iron atom tetrahedrally bound to four
cysteinyl sulfur atoms, a metal center similar to that
found in rubredoxin (Rd) type proteins. The simplicity
of the active center in Dx and the possibility of replacing
the iron by other metals make this protein an attractive
case for the crystallographic analysis of metal-substituted
derivatives. This study extends the relevance of Dx to
the bioinorganic chemistry field and is important to obtain
model compounds that can mimic the four sulfur coordination
of metals in biology. Metal replacement experiments were
carried out by reconstituting the apoprotein with In3+,
Ga3+, Cd2+, Hg2+, and
Ni2+ salts. The In3+ and Ga3+
derivatives are isomorphous with the iron native protein;
whereas Cd2+, Hg2+, and Ni2+
substituted Dx crystallized under different experimental
conditions, yielding two additional crystal morphologies;
their structures were determined by the molecular replacement
method. A comparison of the three-dimensional structures
for all metal derivatives shows that the overall secondary
and tertiary structures are maintained, while some differences
in metal coordination geometry occur, namely, bond lengths
and angles of the metal with the sulfur ligands. These
data are discussed in terms of the entatic state theory.