Figure 4.

Comparison of Ca²⁺-bound and Mg²⁺-bound BtuB. (A) Ca²⁺ coordination after 30 ns. Residues interacting with the Ca²⁺ ions (yellow) are shown as sticks, colored by atom name. Gln191 is partially transparent so as not to obscure Asp193 behind it. (B) Mg²⁺ coordination after 30 ns. (C) RMSD of the extracellular loops vs. time for the simulation of the Mg²⁺-bound structure (red) compared to the simulation of the Ca²⁺-bound BtuB (black).