TLR1

TLR1 (Toll-like receptor 1) is a cell-surface pattern-recognition receptor that functions as a key component of innate immunity through the detection of microbial lipoproteins and lipopeptides^[1][2]. TLR1 exerts its biological activity primarily by forming a heterodimer with TLR2, enabling selective recognition of triacylated lipopeptides and subsequent activation of inflammatory signaling pathways, including NF-κB-dependent responses^[1][2]. Mechanistically, structural studies demonstrated that triacylated ligands such as Pam₃CSK₄ promote formation of an active TLR1-TLR2 signaling complex, in which the lipid moieties occupy distinct hydrophobic binding pockets within TLR1 and TLR2, thereby facilitating receptor dimerization and downstream signal transduction^[2]. This ligand discrimination property distinguishes TLR1 from the closely related isoform TLR6, which also heterodimerizes with TLR2 but preferentially recognizes diacylated lipopeptides because of structural differences in its ligand-binding region^[1][2]. In disease-relevant and experimental settings, TLR1 contributes to host responses against bacterial and mycobacterial components, and TLR1-deficient macrophages display impaired pro-inflammatory cytokine production following stimulation with mycobacterial lipoproteins or synthetic triacylated lipopeptides^[1]. For experimental applications, the synthetic triacylated lipopeptide Pam₃CSK₄ is widely used as a selective TLR1-TLR2 agonist to investigate innate immune signaling, receptor activation mechanisms, and inflammatory responses in cellular and animal models^[1][2].