TtcA a new tRNA-thioltransferase with an Fe-S cluster

Abstract

TtcA catalyzes the post-transcriptional thiolation of cytosine 32 in some tRNAs. The enzyme from Es-cherichia coli was homologously overexpressed in E. coli. The purified enzyme is a dimer containing an iron–sulfur cluster and displays activity in in vitro as-says. The type and properties of the cluster were in-vestigated using a combination of UV-visible absorp-tion, EPR and Mössbauer spectroscopy, as well as by site-directed mutagenesis. These studies demon-strated that the TtcA enzyme contains a redox-active and oxygen-sensitive [4Fe-4S] cluster, chelated by only three cysteine residues and absolutely essen-tial for activity. TtcA is unique tRNA-thiolating en-zyme using an iron–sulfur cluster for catalyzing a non-redox reaction

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