FIGURE 3. Active site of BluB.

a, b, The active site with oxidized FMN (a) and reduced FMN (b), viewed from the re-face. H-bonds are represented as dashed lines. For clarity, water molecules are not rendered in this view. The rearrangement in H-bonds around N1 reflects the change in protonation in the reduced structure. Asp 32 may also form a close contact with C1' of the ribityl chain, suggesting a potential catalytic role for this residue. c, d, Side views of the active site in the oxidized (c) and reduced (d) structures. For clarity, Arg 34 has not been rendered in this view. The sigma-A weighted 2F_o-F_c electron density map is contoured at 1 and coloured grey (around protein side chains), blue (around FMN/FMNH₂) and red (around water/oxygen) to enhance contrast.