Influence of haem environment on the catalytic properties of the tetrathionate reductase TsdA from Campylobacter jejuni

Julia M. Kurth, Julea N. Butt, David J. Kelly, Christiane Dahl

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Abstract

Bifunctional diheme cytochrome c thiosul­fate dehydrogenases/tetrathionate reductases (TsdA) exhibit different catalytic properties depend­ing on the source organism. In the human food-borne intestinal pathogen Campylobacter jejuni , TsdA functions as a tetrathionate reductase en­abling respiration with tetrathionate as an al­ternative electron acceptor. Here, evidence is provided that Cys138 and Met255 serve as the sixth ligands of Heme 1 and Heme 2, respec­tively, in the oxidized Cj TsdA wt protein. Re­placement of Cys138 resulted in a virtually inac­tive enzyme, confirming Heme 1 as the active site heme. Significantly, TsdA variants carrying amino acid exchanges in the vicinity of the elec­tron-transferring Heme 2 (Met255, Asn254 and Lys252) exhibited markedly altered catalytic properties of the enzyme, showing these residues play a key role in the physiological function of TsdA. The growth phenotypes and tetrathionate reductase activities of a series of Δ tsdA/*tsdA complemen­tation strains constructed in the original host C. jejuni 81116, showed that in vivo , the TsdA variants exhibited the same catalytic properties as the pure, recombinantly produced enzymes. However, variants that catalyzed tetrathionate reduction more effectively than the wild-type enzyme did not allow better growth.
Original languageEnglish
Article numbere00422
JournalBioscience Reports
Volume36
Issue number6
Early online date27 Oct 2016
DOIs
Publication statusPublished - 9 Dec 2016

Keywords

  • axial heme ligation
  • reaction directionality
  • thiosulfate
  • tetrathionate reductase
  • cytochrome c

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