Mutating Amino Acids to Analyze the Effects on NADase Activity in Uropathogenic Escherichia coli and Acinetobacter baumannii TIR proteins

Abstract Toll/interleukin-1 receptor/resistance protein (TIR) domains are crucial components in the innate immune system. In mammalian cells, TIR domains are found in Toll-like receptors (TLRs) which activate innate immune responses upon recognition of pathogen-associated molecular patterns and danger-associated molecular patterns. In contrast, TIR domains in prokaryotic cells may be linked to bacterial evasion of the innate immune system. To evade immune system defenses, Uropathogenic E. coli utilize TIR domains, like TcpC, to inhibit TLR signaling pathways. TcpC also has NADase activity which could have a role in immune evasion; we are interested in identifying amino acids important for TcpC’s NADase activity. Previously, we were able to determine that a conserved amino acid, glutamate, is important for NADase activity and that a conserved aspartic acid was crucial for NADase functionality for the additional bacterial TIR protein found in bacteria Acenitobacter baumanii (AbTIR). We hypothesized that the conserved aspartic acid may play a role in TcpC NADase activity. To support our hypothesis, we created an aspartic acid (D) to alanine (A) mutation using site-directed mutagenesis, tested to see if the mutation in TcpC affected NADase activity, and compared the effect of the TcpC DA mutation with the DA mutation from AbTIR. Results show that the DA mutants lost NADase activity, suggesting that the conserved aspartic acid is important for NADase activity in both TcpC and AbTIR. By determining which amino acids are critical for NADase activity, we can use this information for drug development for diseases that might be associated with TIR activity and innate immune evasion. Funded by NIH R25Act GM058264