Vaccinia virus (VACV) encodes many proteins that interfere with the host immune system. Vaccinia virus A46 protein specifically targets the BB-loop motif of TIR-domain-containing proteins to disrupt receptor:adaptor (e.g., TLR4:MAL and TLR4:TRAM) interactions of the toll-like receptor signaling. The crystal structure of A46 (75-227) determined at 2.58 Å resolution showed that A46 formed a homodimer and adopted a Bcl-2-like fold similar to other VACV proteins such as A52, B14, and K7. Our structure also revealed that VIPER (viral inhibitory peptide of TLR4) motif resides in the α1-helix and six residues of the VIPER region were exposed to surface for binding to target proteins. In vitro binding assays between wild type and six mutants A46 (75-227) and full-length MAL identified critical residues in the VIPER motif. Computational modeling of the A46:MAL complex structure showed that the VIPER region of A46 and AB loop of MAL protein formed a major binding interface. In summary, A46 is a homodimer with a Bcl-2-like fold and VIPER motif is believed to be involved in the interaction with MAL protein based on our binding assays.
Keywords: VIPER motif; innate immunity; toll-like receptor; vaccinia virus.
© 2014 The Protein Society.