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Science 339 (6126): 1426-1429

Copyright © 2013 by the American Association for the Advancement of Science

Structural Reorganization of the Toll-Like Receptor 8 Dimer Induced by Agonistic Ligands

Hiromi Tanji1,3,*, Umeharu Ohto1,3,*, Takuma Shibata2, Kensuke Miyake2, and Toshiyuki Shimizu1,3,{dagger}

1 Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
2 Division of Innate Immunity, Department of Microbiology and Immunology, Laboratory of Innate Immunity, Center for Experimental Medicine and Systems Biology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
3 RIKEN SPring-8 Center, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan.


Figure 1
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Fig. 1. Structures of human TLR8. (A) Schematic representation of the domain organization of extracellular regions of human TLR8 (hTLR8). LRRs are indicated by numbered boxes. The protruding LRR loops and the long insertion region between LRR14 and LRR15 (Z-loop) that are characteristic of the TLR7-9 family are indicated by curved lines above the LRRs. The regions missing from the structural model are indicated by red dashed lines. The N-terminal and C-terminal halves of TLR8 are shown in light green and light orange, respectively. (B) Monomer structure of the hTLR8-CL097 complex showing the lateral face (left) and the convex face from the N-terminal side (right). The bound CL097, N-glycan residues, and disulfide bonds are shown in stick representations. The O, N, and S atoms are colored red, blue, and orange, respectively. The C atoms of CL097 and N-glycans are shown in yellow and gray, respectively. The N and C termini of each fragment are shown as spheres. (Left) Front and (right) side views of the preformed inactivated state (C) and ligand-induced activated state (D). TLR8 and its dimerization partner TLR8* are green and cyan, respectively. The CL097 molecules in the activated dimerization interface are illustrated by space-filling representations. The distances between the two Cα atoms of each C terminus are indicated.

 

Figure 2
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Fig. 2. Dimerization interface of the ligand-induced TLR8 dimer. (Left, middle) A surface representation of the protein-protein interface (orange) and ligand-mediated interface (red). (Right, middle) Top view of the ligand-induced TLR8 dimer along the two-fold NCS axis. Magnified views of the central dimerization interface around the two-fold NCS axis (top) and the peripheral dimerization interface (bottom). Hydrogen bonds in the magnified views are indicated by dashed lines.

 

Figure 3
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Fig. 3. Ligand recognition sites of TLR8. (A), (B), and (C) Residues involved in the interaction of TLR8 with CL097, CL075, and R848, respectively. The C atoms of the ligand molecules are yellow. Water molecules mediating the ligand recognition are indicated by red filled circles, and hydrogen bonds by dashed lines. The chemical structures of these ligands are shown at top right in each panel. (D), (E), and (F) NF-{kappa}B activity of human TLR8 mutants, stimulated by CL097, CL075, and R848, respectively. The reactivity of wild type and various mutants of TLR8 were analyzed by an NF-{kappa}B–dependent green fluorescent protein reporter assay using Ba/F3 cells. Data represent the fold NF-{kappa}B induction, calculated as mean fluorescence intensity (MFI) of stimulated cells divided by MFI of nonstimulated cells. Dotted lines indicates the fold induction as 1. Data shown are representative of three independent experiments.

 

Figure 4
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Fig. 4. Conformational change in TLR8 induced by binding to agonistic ligands. The unliganded, inactivated form of TLR8 (A) transforms into the activated form (B) upon ligand binding. The overall conformational change is illustrated schematically (C). The conformational changes are represented by ring rotations and hinge motions, both of which are indicated by gray arrows.

 


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