Table 7.

Differential or mechanistically relevant amino acids in species-specific binding to the phosphates of Lipid IVA.

Human TLR4	Murine TLR4	Equine TLR4
hLys58c	mAsn58c	eGlu58c
hGlu369b is reinforced by Asp371b repelling P2.	mLys367b remains attractive to P1 by Ala369b.	eGlu370b is neutralized in salt bridge with Lys372b.
No arginine, but Gly384a, cf. hGln436b.	mArg434b is equivalent to eArg385a to attract P1.	eArg385a is equivalent to mLys367b to attract P1
hLys388b	mSer386b	eLys389b
hLys388b is in salt bridges with Glu369b or Glu321a.	mSer386b has hydrogen-bond with Lys341a.	eLys389b forms a salt bridge with Glu344a.
hGly343a without interaction, but adjacent Glu321a is in a salt bridge with Arg322a.	mLys341a shifts from H-bond to form a stronger salt bridge with P.	eGlu344a is in salt bridge with Arg342a.
hGln436b	mArg434b	eGln437b
No cationic attraction to direct P2 into the agonist position.	Cationic mArg434b attracts P1 to direct the phosphate group into the agonist position.	Ridge of ion bridges and H-bonds: Glu394b+Lys389b Lys372b+Glu370b to ramp up P1 from the groove (TLR4*/MD-2 interface) to the wedge (TLR4/TLR4* interface)
No cationic attraction for P2 in wedge. P cannot mediate the TLR4*/MD-2 contact in the wedge, where it is attracted by hLys89c and hArg90c, disrupting the TLR4*/MD-2 interface near hGlu439b. Dimerization is not enabled.	mLys341a, mLys367b, mArg434b form cationic attraction for P1 in wedge. P1 can mediate the TLR4*/MD-2 contact in the wedge. The amide-bound fatty acid FA1 of Lipid IVA partially replaces FA1 of LPS in the TLR4*/MD-2 interface. Dimerization is established.	eLys366a, eArg385a, eLys389b attracts P1 in wedge. Only weakly, P1 mediates the TLR4*/MD-2 contact in the wedge since P1 is more attached to the TLR4 side than to TLR4*. The amide-bound fatty acid FA1 of Lipid IVA (in analogy to FA1 of LPS) may assist the TLR4*/MD-2 formation. Dimerization can be established.
Antagonist activity	Agonist activity	Partial agonist activity