Structures and interface mapping of the TIR domain-containing adaptor molecules involved in interferon signaling.Enokizono, Y., Kumeta, H., Funami, K., Horiuchi, M., Sarmiento, J., Yamashita, K., Standley, D.M., Matsumoto, M., Seya, T., Inagaki, F.
(2013) Proc.Natl.Acad.Sci.USA 110: 19908-19913
- PubMed: 24255114
- DOI: 10.1073/pnas.1222811110
- Primary Citation of Related Structures:  2M1X
- PubMed Abstract:
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 ...
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.
Department of Structural Biology, Faculty of Advanced Life Science, Hokkaido University, N-21, W-11, Kita-ku, Sapporo 001-0021, Japan.