Structure of the <i>B. anthracis</i> IsdX1 NEAT domain.

<p>The ribbon structure of the heme-bound form of IsdX1 is shown. NEAT domains share a conserved β-barrel fold including a 3₁₀-helix (green) that conventionally begins with a serine and ends with a tyrosine, and eight β-strands (teal). The two tyrosine residues (Tyr-109 and Tyr-113) within the heme-binding sequence YXXXY are indicated in purple. Tyr-109 non-covalently binds to the iron atom within the heme molecule at a predicted distance of 2.2 Å. Tyr-113 H-bonds with Tyr-109 as indicated by the dotted black line (2.4 Å). Ser-24 (green) H-bonds with the buried propionate group of the heme porphyrin, increasing binding affinity (2.6 Å). PDB code: 3SIK; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104794#pone.0104794-Ekworomadu1" target="_blank">[36]</a>.