The Brucella TIR-like protein TcpB interacts with the death domain of MyD88

The pathogen Brucella melitensis secretes a Toll/interleukin-1 receptor (TIR) domain containing protein that abrogates host innate immune responses. In this study, we have characterized the biochemical interactions of Brucella TIR-like protein TcpB with host innate immune adaptor proteins. Using protein-fragment complementation assays based on Gaussia luciferase and green fluorescent protein, we find that TcpB interacts directly with MyD88 and that this interaction is significantly stronger than the interaction of TcpB with TIRAP, the only other adaptor protein that detectably interacts with TcpB. Surprisingly, the TcpB–MyD88 interaction depends on the death domain (DD) of MyD88, and TcpB does not interact with the isolated TIR domain of MyD88. TcpB disrupts MyD88DD-MyD88DD, MyD88DD-MyD88TIR and MyD88DD-MyD88 interactions but not MyD88–MyD88 or MyD88TIR-MyD88TIR interactions. Structural models consistent with these results suggest how TcpB might inhibit TLR signaling by targeting MyD88 via a DD–TIR domain interface.

► Pathogen protein TcpB targets host proteins and interferes with host innate immune response.
► Protein complementation assays show that TcpB interacts with death domain of MyD88.
► TcpB was identified as a TIR domain protein, and thus thought to interact via TIR–TIR interactions.