title: Autoinhibition and relief mechanism by the proteolytic processing of Toll-like receptor 8.
abstract: Toll-like receptor 8 (TLR8) senses single-stranded RNA (ssRNA) and initiates innate immune responses. TLR8 requires proteolytic cleavage at the loop region (Z-loop) between leucine-rich repeat (LRR) 14 and LRR15 for its activation. However, the molecular basis of Z-loop processing remains unknown. To elucidate the mechanism of Z-loop processing, we performed biochemical and structural studies of how the Z-loop affects the function of TLR8. TLR8 with the uncleaved Z-loop is unable to form a dimer, which is essential for activation, irrespective of the presence of agonistic ligands. Crystallographic analysis revealed that the uncleaved Z-loop located on the ascending lateral face prevents the approach of the dimerization partner by steric hindrance. This autoinhibition mechanism of dimerization by the Z-loop might be occurring in the proteins of the same subfamily, TLR7 and TLR9.
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan;
authors.forename: Hiromi
authors.initials: H
authors.lastname: Tanji
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan;
authors.forename: Umeharu
authors.initials: U
authors.lastname: Ohto
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Motoi
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan.
authors.forename: Takuma
authors.initials: T
authors.lastname: Shibata
authors.affiliation: Division of Innate Immunity, Department of Microbiology and Immunology, Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Miyake
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan; shimizu@mol.f.u-tokyo.ac.jp.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Shimizu
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D018360:Crystallography, X-Ray; D019281:Dimerization; D017930:Genes, Reporter; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D051200:Toll-Like Receptor 8 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D008024:Ligands; D016328:NF-kappa B; D011993:Recombinant Fusion Proteins; C495349:TLR8 protein, human; D051200:Toll-Like Receptor 8; D010447:Peptide Hydrolases
keywords: Toll-like receptor; X-ray crystallography; Z-loop; innate immunity; proteolytic processing