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. 2013 Aug 8;7:e201305003. doi: 10.5936/csbj.201305003

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© Scior et al.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly cited.

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Schematic view of the computed side chain interactions of the complete human TLR4 ectodomain/MD-2 complex with Lipid IVA pointing out the receptor antagonistic action of Lipid IVA in the human system. Note the inverted (flipped) orientation of the sugar-phosphate backbone as compared to the agonistic binding of lipid A/LPS to human TLR4/MD-2 as well as to the agonistic interaction of Lipid IVA with murine TLR4/MD-2 (see Fig. 7). The indicated charged/polar side chains of counter-TLR4* form a “repulsion region” that prevents the association of the TLR4/MD-2/Lipid IVA unit in the human system. As a direct consequence Lipid IVA does not provide the dimerization into an active m-shaped receptor complex in the human system and acts as a competitive inibitor of LPS/lipid A (agonist) binding instead. Counter-subunit TLR4* is leaving or never was in place, which is indicated by the shaded label of TLR4* (upper left side of wedge).