The structure of the human MD-2 with bound endotoxin.

<p>(A) Human MD-2 (pdb id 3FXI, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107520#pone.0107520-Park1" target="_blank">[27]</a>) is shown in grey ribbon. The side chains of amino acid residues at positions 82 (valine), 122 (lysine) and 125 (lysine) are shown in stick representation. These amino acid residues are positioned at the entrance to the binding pocket and come in close proximity to the ligand (here the hexaacylated endotoxin, shown in yellow). Figure was prepared with the USCF Chimera package <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107520#pone.0107520-Pettersen1" target="_blank">[26]</a>. (B) Amino acid alignment of residues at positions 82, 122 and 125 of human, murine and equine MD-2 (red – acidic amino acid; blue – basic amino acid; green – nonpolar/hydrophobic amino acid). (C) The structure of lipid A. The arrows indicate acyl chains that are absent in the structure of the msbB endotoxin and in lipid IVa.