G-108 Subversion of innate immune responses by microbial TIR interacting proteins.

Abstract

Microbial pathogens have evolved mechanisms to regulate and evade innate immunity. One mechanism involves the subversion of innate immune signaling by microbial TIR Interacting Proteins (TIPs). TIPs are thought to function by disruption of host Toll/IL-1 receptor (TIR) signaling. Both bacterial and viral TIPs have been identified. We have determined the crystal structure of MyD88 and characterized its interactions with the bacterial TIP protein, TcpC from uropathogenic E. coli CFT073. Both soluble TcpC protein and derived peptides are capable to inhibit TIR signaling. NMR solution studies map the binding of TcpC and derived peptides to a region near the oncogenic mutation MyD88-L265P. This gain of function somatic mutation, associated with nearly one third of all diffuse large B cell lymphomas, 90% of Waldenström macroglobulinemia (WM) and 54% of immunoglobulin M monoclonal gammopathy, correlates with tumor cell proliferation and survival involving chronic activation of MYD88-dependent NF-kB and Janus Kinase signaling pathways. We now report the X-ray crystal structure of the bacterial TIP protein TcpB from Brucella and characterize its interaction with TIRAP. The structure of TcpB reveals the BB loop microtubule-binding site as well as a symmetrical dimer involving the DD and EE loops. These studies identify a set of candidate TcpB blocking peptides. A comparison between the microbial TcpB, TIRAP and MyD88 crystal structures reveal structural differences involving distinct loop positions. These findings provide a framework for identification and development of novel microbial derived therapeutics targeting the oncogenic mutation MyD88-L265P, microbial pathogenesis and inflammation.