title: Ligand-independent oligomerization of TLR4 regulated by a short hydrophobic region adjacent to the transmembrane domain.
abstract: Toll-like receptors (TLRs) are key receptors for the activation of immune responses directed against pathogens. Among the more than 10 identified TLRs, TLR4 is the most unique because it associates with a variety of adaptor molecules for ligand recognition and signal transduction. However, the relationship between the unique characteristics and structural features of TLR4 is poorly defined. In this study, we demonstrate a novel biochemical characteristic of TLR4. TLR4, but not other TLRs, was observed as highly aggregated forms in immunoblotting. Interestingly, substitution of the transmembrane and cytoplasmic domain of TLR4 with those of other TLRs completely abolished the aggregation of TLR4. Furthermore, we found a short hydrophobic region (HR) adjacent to the transmembrane domain of TLR4; the TLR4 mutant lacking the HR was not aggregated and was nonfunctional in response to lipopolysaccharide. These results suggest that the HR may play a critical role in the functional oligomerization of TLR4.
authors.affiliation: Department of Cellular Pharmacology, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan. nishiya@med.hokudai.ac.jp
authors.forename: Tadashi
authors.initials: T
authors.lastname: Nishiya
authors.forename: Emi
authors.initials: E
authors.lastname: Kajita
authors.forename: Soichi
authors.initials: S
authors.lastname: Miwa
mesh_terms: D000818:Animals; D002460:Cell Line; D003713:Dendritic Cells / Q000502:physiology; D006031:Glycosylation; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D051218:Lymphocyte Antigen 96 / Q000172:deficiency; D008264:Macrophages / Q000502:physiology; D051379:Mice; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000737:chemistry*
chemical_list: D008024:Ligands; C411728:Ly96 protein, mouse; D051218:Lymphocyte Antigen 96; D011993:Recombinant Fusion Proteins; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4