Metal binding to the tetrathiolate motif of desulforedoxin and related polypeptides

Matthew Kennedy, Lian Yu, Maria João Lima, Carla S. Ascenso, Christopher Czaja, Isabel Moura, Jose J. G. Moura, Frank Rusnak

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Desulforedoxin and the N-terminus of desulfoferrodoxin share a 36 amino acid domain containing a (Cys-S)4 metal binding site. Recombinant forms of desulforedoxin, an N-terminal fragment of desulfoferrodoxin, and two desulforedoxin mutant proteins were reconstituted with Fe3+, Cd2+, and Zn2+ and relative metal ion affinities assessed by proton titrations. Protons compete with metal for protein ligands, a process that can be followed by monitoring the optical spectrum of the metal-protein complex as a function of pH. For all polypeptides, Fe3+ bound with the highest affinity, whereas the affinity of Zn2+ was greater than Cd2+ in desulforedoxin and the N-terminal fragment of desulfoferrodoxin, but this order was reversed in desulforedoxin mutant proteins. Metal binding in both mutants was significantly impaired. Furthermore, the Fe3+ complex of both mutants underwent a time-dependent bleaching process which coincided with increased reactivity of cysteine residues to Ellman's reagent and concomitant metal dissociation. It is hypothesized that this results from an autoredox reaction in which Fe3+ is reduced to Fe2+ with attendant oxidation of ligand thiols.

Original languageEnglish
Pages (from-to)643-649
Number of pages7
JournalJournal of Biological Inorganic Chemistry
Volume3
Issue number6
DOIs
Publication statusPublished - 1 Dec 1998

Keywords

  • Desulfoferrodoxin
  • Iron sulfur protein
  • Metal affinity
  • Nonheme iron protein
  • Rubredoxin

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