Secondary Dimerisation Interface

There are four monomers in TLR5-FliC complex: TLR5, TLR5', FliC and FliC'. Three surfaces form the secondary dimerisation interface: interface-α (TLR5-FliC'), interface-α' (TLR5'-FliC) and interface-β (TLR5-TLR5'). There is no interaction between FliC and FliC'.

Figure 4.1. Secondary dimerisation in the 2:2 TLR5-FliC assembly. 

Interface α and α' are shown in green which represent hydrogen bonding. Interface β comprises of hydrophobic (orange) and hydrogen bond (pink) interactions.

Interface-α and interface-α'

Figure 4.2. Hydrogen bonds in interface-α and interface-α'. 

In interface α, Asp381' of TLR5' acts as an acidic residue and forms 3 hydrogen bonds with FliC Lys135, Gln128 and Gln 130. Interface α' is the reciprocal of interface α, hence the same residues are involved in hydrogen bonding between TLR5 and FliC'.   

Interface-β

Interface β has two different interactions. Four hydrogen bonds and a hydrophobic core bring both TLR5 and TLR5' together. 

Figure 4.3. Hydrogen bonds in interface-β

Four hydrogen bonds constitute part of the interface-β. 6 residues are involved in hydrogen bonding. The 4 hydrogen bonds are between: 

1. Arg377 and Asn350'

2. Arg377 and Tyr373' 

3. Arg377' and Asn350 

4. Arg377' and Tyr373

Figure 4.4. Hydrophobic core in interface-β

The hydrophobic core is created by Van der Waals force between two sets of 3 aromatic residues (Phe273, Phe351 and His375 of TLR5 and TLR5'). 6 residues are involved in this hydrophobic core.