5 years ago

Nonredox thiolation in tRNA occurring via sulfur activation by a [4Fe-4S] cluster [Chemistry]

Nonredox thiolation in tRNA occurring via sulfur activation by a [4Fe-4S] cluster [Chemistry]
Nadia Touati, Sylvain Caillat, Simon Arragain, Beatrice Golinelli–Pimpaneau, Laurent Binet, Ornella Bimai, Mohamed Atta, Jean–Luc Ravanat, Marc Fontecave, Pierre Legrand

Sulfur is present in several nucleosides within tRNAs. In particular, thiolation of the universally conserved methyl-uridine at position 54 stabilizes tRNAs from thermophilic bacteria and hyperthermophilic archaea and is required for growth at high temperature. The simple nonredox substitution of the C2-uridine carbonyl oxygen by sulfur is catalyzed by tRNA thiouridine synthetases called TtuA. Spectroscopic, enzymatic, and structural studies indicate that TtuA carries a catalytically essential [4Fe-4S] cluster and requires ATP for activity. A series of crystal structures shows that (i) the cluster is ligated by only three cysteines that are fully conserved, allowing the fourth unique iron to bind a small ligand, such as exogenous sulfide, and (ii) the ATP binding site, localized thanks to a protein-bound AMP molecule, a reaction product, is adjacent to the cluster. A mechanism for tRNA sulfuration is suggested, in which the unique iron of the catalytic cluster serves to bind exogenous sulfide, thus acting as a sulfur carrier.

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