Endotoxin recognition molecules, Toll-like receptor 4-MD-2.

Toll-like receptors (TLRs) are innate pathogen recognition molecules for microbial products. Lipopolysaccharide (LPS), a membrane constituent of Gram-negative bacteria, is one of the most potent microbial products. LPS is recognized by TLR4 and MD-2. TLR4 is a transmembrane protein, the extracellular domain of which is composed of a protein motif called leucine-rich repeats (LRR). MD-2 is an extracellular molecule that is associated with the extracellular LRR of TLR4. MD-2 has a role in cell surface expression of TLR4 and interaction with LPS. TLR4-MD-2 contributes to containment of infections by Gram-negative bacteria by activating immune responses.