A traffic light enzyme: acetate binding reversibly switches chlorite dismutase from a red- to a green-colored heme protein

Durga Mahor, Julia Püschmann, Menno van den Haak, Pepijn J. Kooij, David L.J. van den Ouden, Marc J.F. Strampraad, Batoul Srour, Peter Leon Hagedoorn

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Abstract

Abstract: Chlorite dismutase is a unique heme enzyme that catalyzes the conversion of chlorite to chloride and molecular oxygen. The enzyme is highly specific for chlorite but has been known to bind several anionic and neutral ligands to the heme iron. In a pH study, the enzyme changed color from red to green in acetate buffer pH 5.0. The cause of this color change was uncovered using UV–visible and EPR spectroscopy. Chlorite dismutase in the presence of acetate showed a change of the UV–visible spectrum: a redshift and hyperchromicity of the Soret band from 391 to 404 nm and a blueshift of the charge transfer band CT1 from 647 to 626 nm. Equilibrium binding titrations with acetate resulted in a dissociation constant of circa 20 mM at pH 5.0 and 5.8. EPR spectroscopy showed that the acetate bound form of the enzyme remained high spin S = 5/2, however with an apparent change of the rhombicity and line broadening of the spectrum. Mutagenesis of the proximal arginine Arg183 to alanine resulted in the loss of the ability to bind acetate. Acetate was discovered as a novel ligand to chlorite dismutase, with evidence of direct binding to the heme iron. The green color is caused by a blueshift of the CT1 band that is characteristic of the high spin ferric state of the enzyme. Any weak field ligand that binds directly to the heme center may show the red to green color change, as was indeed the case for fluoride.

Original languageEnglish
Pages (from-to)609-620
Number of pages12
JournalJournal of Biological Inorganic Chemistry
Volume25
Issue number4
DOIs
Publication statusPublished - 2020

Keywords

  • Acetate binding
  • Charge transfer band
  • Chlorite dismutase
  • Electron paramagnetic resonance (EPR)
  • Green heme protein

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