Superoxide reductase from Giardia intestinalis: Structural characterization of the first SOR from a eukaryotic organism shows an iron centre that is highly sensitive to photoreduction

Cristiana M. Sousa, Philippe Carpentier, Pedro M. Matias, Fabrizio Testa, Filipa Pinho, Paolo Sarti, Alessandro Giuffrè, Tiago M. Bandeiras, Célia V. Romão

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Superoxide reductase (SOR), which is commonly found in prokaryotic organisms, affords protection from oxidative stress by reducing the superoxide anion to hydrogen peroxide. The reaction is catalyzed at the iron centre, which is highly conserved among the prokaryotic SORs structurally characterized to date. Reported here is the first structure of an SOR from a eukaryotic organism, the protozoan parasite Giardia intestinalis (GiSOR), which was solved at 2.0Å resolution. By collecting several diffraction data sets at 100K from the same flash-cooled protein crystal using synchrotron X-ray radiation, photoreduction of the iron centre was observed. Reduction was monitored using an online UV-visible microspectrophotometer, following the decay of the 647nm absorption band characteristic of the iron site in the glutamate-bound, oxidized state. Similarly to other 1Fe-SORs structurally characterized to date, the enzyme displays a tetrameric quaternary-structure arrangement. As a distinctive feature, the N-terminal loop of the protein, containing the characteristic EKHxP motif, revealed an unusually high flexibility regardless of the iron redox state. At variance with previous evidence collected by X-ray crystallography and Fourier transform infrared spectroscopy of prokaryotic SORs, iron reduction did not lead to dissociation of glutamate from the catalytic metal or other structural changes; however, the glutamate ligand underwent X-ray-induced chemical changes, revealing high sensitivity of the GiSOR active site to X-ray radiation damage.

Original languageEnglish
Pages (from-to)2236-2247
Number of pages12
JournalActa Crystallographica Section D-Biological Crystallography
Volume71
DOIs
Publication statusPublished - 2015

Keywords

  • eukaryotes
  • oxidative stress
  • radiation damage
  • superoxide reductase
  • visible spectroscopy

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