Fig. 2. Significant structural features of ArnT_Cm.

(A) Three views of ArnT_Cm in spacefill representation showing the location of notable cavities in the structure. The middle view has the same orientation as the view in (B). The other two are obtained by 45° rotation in opposite directions around a vertical axis. Cavities are color coded as in (B), where their identity is labeled. (B) Ribbon representation of ArnT_Cm showing the volumes of notable cavities in the structure. Volumes were calculated using the Voss Volume Voxelator server (22), using probes with 15 and 1.75 Å radii, corresponding to the outer and inner probe, respectively. The approximate membrane boundaries are shown as black lines. (C) Close-up of the metal coordination site in ArnT_Cm showing Zn⁺² as a purple sphere and the coordinating residues colored by heteroatom. The dashed red line box in (B) shows the overall location of the coordination site. (D) The effect of mutations in Zn⁺² coordinating residues on ArnT_Se expressed in a BL21(DE3)ΔarnT E. coli strain for rescue of polymyxin B (PMXB) resistance (13). Corresponding residue numbers in ArnT_Cm are shown in parentheses here and in all subsequent figures. OD₆₀₀, optical density at 600 nm. Data presented are means + SD. N is shown for each data column.