Figure 1.

Crystal structures of the unliganded and CO-bound HbI. The HbI homodimer subunits are colored dark and light gray. Purple sticks represent the prosthetic heme group. Iron is colored green. CO is colored blue. The structures of unliganded HbI (left) and CO-HbI (right) are generated from the PDB entries 4SDH and 3SDH, respectively. Interfacial helices E and F are shown at the bottom, to highlight the conformational transition undergone by Phe 97 (red) upon CO binding. The structural representation was drawn using VMD.²⁶