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Characterization of a pre-export enzyme-chaperone complex on the twin-arginine transport pathway.

Abstract : The Tat (twin-arginine translocation) system is a protein targeting pathway utilized by prokaryotes and chloroplasts. Tat substrates are produced with distinctive N-terminal signal peptides and are translocated as fully folded proteins. In Escherichia coli, Tat-dependent proteins often contain redox cofactors that must be loaded before translocation. Trimethylamine N-oxide reductase (TorA) is a model bacterial Tat substrate and is a molybdenum cofactor-dependent enzyme. Co-ordination of cofactor loading and translocation of TorA is directed by the TorD protein, which is a cytoplasmic chaperone known to interact physically with the TorA signal peptide. In the present study, a pre-export TorAD complex has been characterized using biochemical and biophysical techniques, including SAXS (small-angle X-ray scattering). A stable, cofactor-free TorAD complex was isolated, which revealed a 1:1 binding stoichiometry. Surprisingly, a TorAD complex with similar architecture can be isolated in the complete absence of the 39-residue TorA signal peptide. The present study demonstrates that two high-affinity binding sites for TorD are present on TorA, and that a single TorD protein binds both of those simultaneously. Further characterization suggested that the C-terminal 'Domain IV' of TorA remained solvent-exposed in the cofactor-free pre-export TorAD complex. It is possible that correct folding of Domain IV upon cofactor loading is the trigger for TorD release and subsequent export of TorA.
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Contributeur : Frank Thomas <>
Soumis le : vendredi 3 juin 2016 - 10:24:10
Dernière modification le : mardi 6 octobre 2020 - 16:12:03

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Jennifer M Dow, Frank Gabel, Frank Sargent, Tracy Palmer. Characterization of a pre-export enzyme-chaperone complex on the twin-arginine transport pathway.. Biochemical Journal, Portland Press, 2013, 452 (1), pp.57-66. ⟨10.1042/BJ20121832⟩. ⟨hal-01326125⟩



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