Therapeutic targeting of intracellular Toll-like and interleukin-1/18 receptor (TIR) resistance domain containing proteins for protection against infection, inflammation and disease

Abstract

Abstract TIR domain containing proteins are important immune associated proteins shared among Toll-like and interleukin-1/18 receptor family members. In a recent discovery select bacterial, plant and human TIR proteins exhibit enzymatic activity in binding and processing nicotinamide adenine dinucleotide (NAD+). Based on their abilities to facilitate signaling across biology, we hypothesize that TIR proteins represent unique therapeutic targets for modulating infection, inflammation and disease. Our previous structural studies of bacterial-host TIR proteins B. melitensis (TcpB) and uropathogenic E. coli CFT073 (TcpC) with human host TIRAP and MyD88 characterized peptides that negatively regulate signaling and infection. From these studies we identified interactions that are at or near reported biological TIR protein interfaces. In particular, we identified a functionally important motif found conserved on the C helix of most bacterial, human host and NAD+ consuming TIR proteins. As proof of concept for select targeting of TIR proteins and this region in particular we have used the TLR4 antagonist, TAK-242, which selectively binds within this motif. Treatment with TAK-242 or TLR4-C747S blocks LPS signaling. Additionally, TAK-242 protected mice from lethal influenza challenge similar to an extracellular TLR4 antagonist, Eritoran. Bioinformatic analysis of the region targeted by TAK242 show that it is located within the WxxxE structural motif identified to be important for protecting against microtubule destabilization and includes a catalytically essential glutamic acid (E) residue conserved among nearly all NAD+ consuming TIR proteins. These studies provide a framework for future studies targeting TIR protein function.