Figure 6.

The effect of mutations in the Fiu external substrate-binding site on the function of Fiu in vivo. A, bar graph indicating the effect of Fiu binding site mutations of the ability of pBAD24Fiu to complement E. coli BW25113 Δ6. The length of the bar graph indicates the maximum concentration of 2,2′-bipyridine at which growth of the complemented strain was observed on solid LB agar; experimental data are shown in Fig. S5. B, stick and cartoon representation of the Fiu extracellular loops, showing the location of the residues in the putative substrate-binding site subjected to mutagenesis. C, magnified view of the Fiu substrate-binding site shown in B, rendered as a surface model with mutated residues labeled (left) and Fe–DHB shown (right). D, stereo image showing the residues mutated in the Fiu external binding site as a stick representation. The Fe–DHB complex is shown as a line and sphere representation for DHB and Fe³⁺, respectively. Colors are consistent through all panels and indicate the effect of mutagenesis on Fiu function: brick red, inactivation or significant defect in Fiu function; pink, minor defection in Fiu function; green, no defect in Fiu function.