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Figure 1.
The three gold-binding sites of wild type SmTGR.A, the
three-dimensional model of one subunit is shown with the three
gold-binding sites. Site 1 shows the gold in between Cys^154 and
Cys^159; site 2 shows the gold in between Cys^520 and Cys^574;
site 3 shows the gold in the putative NADPH-binding pocket. The
glutaredoxin domain of TGR is shown in green, whereas the
thioredoxin domain is shown in red. The bound flavin is also
highlighted. B, site 1. The linear geometry of the
Cys^154-gold-Cys^159 adduct is shown. The occupancy of the gold
atom is about 50%. Both distances of the sulfur-gold bond are
2.3 Å, as expected for this type of coordination moiety.
C, site 2. The electron density map (2F[o] − F[c]) contoured
at 1 σ shows the possible charge transfer complex between the
gold and Phe^505. D, site 2. The gold atom between Cys^574 and
Cys^520 is shown together with the other residues that surround
the metal, i.e. Phe^505, Pro^507, and Pro^542. E, site 3. Gold
in the putative NADPH-binding site of SmTGR. Tyr^296 is known to
swing upon NADPH binding in thiol reductase enzymes (30).
Ser^295 is the residue closest to the gold (Ser^295(OG)-gold:
3.2 Å). Other van der Waals' contacts are with the main
chain atoms of the polypeptide (Ala^390, Val^391, Gly^392, and
Arg^393).
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