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Figure 2.
Figure 2. Crystal structures of FecA unliganded (a,
FecA[apo]), bound with iron-free dicitrate (b, FecA[Cit]) and
with diferric dicitrate (c, FecA[FeCit]), viewed perpendicular
to the barrel axis. In all three structures, the overall fold
consists of a 22-stranded b-barrel (yellow) preceded by a plug
domain (magenta) that fits into the barrel lumen. Iron-free
dicitrate and diferric dicitrate (green) are depicted in
space-filling representation (with iron atoms in red). The two
extracellular loops L7 and L8, which are involved in
conformational changes upon binding of diferric dicitrate, are
colored blue. The TonB box motifs in FecA[apo] and FecA[Cit] are
circled. Part of the barrel has been rendered transparent to
reveal the plug domain located in the barrel lumen.
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