Identification of a unique TLR2-interacting peptide motif in a microbial leucine-rich repeat protein

► Leucine-rich repeat (LRR) domain of a bacterial protein activates TLR2. ► Peptide repeats in the LRR domain responsible for TLR2 activation were identified. ► A common peptide motif in these repeats interacts with TLR2. ► This peptide motif in a TLR2-dependent manner activates macrophages. ► This study identifies a novel non-acylated peptide ligand of TLR2. Pathogenesis of many bacterially-induced inflammatory diseases is driven by Toll-like receptor (TLR) mediated immune responses following recognition of bacterial factors by different TLRs. Periodontitis is a chronic inflammation of the tooth supporting apparatus often leading to tooth loss, and is caused by a Gram-negative bacterial consortium that includes Tannerella forsythia. This bacterium expresses a virulence factor, the BspA, which drives periodontal inflammation by activating TLR2. The N-terminal portion of the BspA protein comprises a leucine-rich repeat (LRR) domain previously shown to be involved in the binding and activation of TLR2. The objective of the current study was to identify specific epitopes in the LRR domain of BspA that interact with TLR2. Our results demonstrate that a sequence motif GC(S/T)GLXSIT is involved in mediating the interaction of BspA with TLR2. Thus, our study has identified a peptide motif that mediates the binding of a bacterial protein to TLR2 and highlights the promiscuous nature of TLR2 with respect to ligand binding. This work could provide a structural basis for designing peptidomimetics to modulate the activity of TLR2 in order to block bacterially-induced inflammation.