Pseudomonas aeruginosa ttcA encoding tRNA-thiolating protein requires an iron-sulfur cluster to participate in hydrogen peroxide-mediated stress protection and pathogenicity

Abstract

Abstract During the translation process, transfer RNA (tRNA) carries amino acids to ribosomes for protein synthesis. Each codon of mRNA is recognized by a specific tRNA, and enzyme-catalysed modifications to tRNA regulate translation. TtcA is a unique tRNA-thiolating enzyme that requires an iron-sulfur ([Fe-S]) cluster to catalyse thiolation of tRNA. In this study, the physiological functions of a putative ttcA in Pseudomonas aeruginosa , an opportunistic human pathogen that causes serious problems in hospitals, were characterized. A P . aeruginosa ttcA -deleted mutant was constructed, and mutant cells were rendered hypersensitive to oxidative stress, such as hydrogen peroxide (H 2 O 2 ) treatment. Catalase activity was lower in the ttcA mutant, suggesting that this gene plays a role in protecting against oxidative stress. Moreover, the ttcA mutant demonstrated attenuated virulence in a Drosophila melanogaster host model. Site-directed mutagenesis analysis revealed that the conserved cysteine motifs involved in [Fe-S] cluster ligation were required for TtcA function. Furthermore, ttcA expression increased upon H 2 O 2 exposure, implying that enzyme levels are induced under stress conditions. Overall, the data suggest that P . aeruginosa ttcA plays a critical role in protecting against oxidative stress via catalase activity and is required for successful bacterial infection of the host.