Structures and interface mapping of the TIR domain-containing adaptor molecules involved in interferon signaling

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 49; pp. 19908 - 19913
• Main Authors: Enokizono, Yoshiaki, Kumeta, Hiroyuki, Funami, Kenji, Horiuchi, Masataka, Sarmiento, Joy, Yamashita, Kazuo, Standley, Daron M., Matsumoto, Misako, Seya, Tsukasa, Inagaki, Fuyuhiko
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 03.12.2013; NATIONAL ACADEMY OF SCIENCES; National Acad Sciences
• Subjects: Adaptor Proteins, Signal Transducing - chemistry; Adaptor Proteins, Signal Transducing - immunology; Adaptor Proteins, Vesicular Transport - chemistry; Adaptor Proteins, Vesicular Transport - immunology; Biological Sciences; Crystal structure; Cytokines; Dimerization; Dimers; Genetic mutation; Humans; Immunoblotting; Immunoprecipitation; Luciferases; Magnetic Resonance Spectroscopy; Models, Biological; Models, Molecular; Molecules; Mutagenesis; Mutation; Protein Conformation; Receptors; Signal transduction; Signal Transduction - immunology; Toll like receptors; Toll-Like Receptors - metabolism; Two hybrid system techniques; Yeasts; TLR signaling; MyD88-independent pathway; innate immunity; TRIF; TRAM
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1222811110

Homotypic and heterotypic interactions between Toll/interleukin-1 receptor (TIR) domains in Toll-like receptors (TLRs) and downstream adaptors are essential to evoke innate immune responses. However, such oligomerization properties present intrinsic difficulties in structural studies of TIR domains. Here, using BB-loop mutations that disrupt homotypic interactions, we determined the structures of the monomeric TIR domain-containing adaptor molecule (TICAM)-1 and TICAM-2 TIR domains. Docking of the monomeric structures, together with yeast two hybrid-based mutagenesis assays, reveals that the homotypic interaction between TICAM-2 TIR is indispensable to present a scaffold for recruiting the monomeric moiety of the TICAM-1 TIR dimer. This result proposes a unique idea that oligomerization of upstream TIR domains is crucial for binding of downstream TIR domains. Furthermore, the bivalent nature of each TIR domain dimer can generate a large signaling complex under the activated TLRs, which would recruit downstream signaling molecules efficiently. This model is consistent with previous reports that BB-loop mutants completely abrogate downstream signaling.