Extracellular domain of the Toll-like receptor. (A) The structure of the leucine-rich repeat (LRR) domain from human TLR3. Notice that the LRR units come together to form a central parallel β sheet that curls to form a concave structure. (B) The structure of a single LRR showing the positions of the residues that are generally approximately conserved. Notice that the leucine residues come together to form a hydrophobic core with the single β strand on one side.

[Drawn from 1ZIW.pdb].