Comparison of the NMR structure of Zn²⁺-t-PhtD and the X-ray crystallographic structure of Zn²⁺-PhtA.

<p>(A) Protein sequences of the two Pht fragments for which three-dimensional structures are known. The PhtD fragment (this study) involves the first histidine triad motif of the Pht family whereas the PhtA fragment (2cs7.pdb, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081168#pone.0081168-RiboldiTunnicliffe1" target="_blank">[43]</a>) contains the second histidine triad motif. Red cylinders (<i>α</i>-helices) and blue arrows (<i>β</i>-strands) indicate experimentally determined secondary structure elements. Residues used for the structural alignment are shaded. Underlined letters identify residues that belong to the PROSITE motif proposed for the identification of histidine triad repeats (see text). (B) Superposition of Zn²⁺-t-PhtD (green) and Zn²⁺-PhtA (violet) structures. Shaded residues in the two Pht sequences are overlayed, as a basis for the superimposition. (C) Zn²⁺-t-PhtD and Zn²⁺-PhtA in the same orientation as in the superimposition. Amino acids bound to Zn²⁺ and the Zn²⁺ ion are shown as sticks and as a sphere, respectively.