Human indoleamine 2,3-dioxygenase is a catalyst of physiological heme peroxidase reactions: implications for the inhibition of dioxygenase activity by hydrogen peroxide

J Biol Chem. 2013 Jan 18;288(3):1548-67. doi: 10.1074/jbc.M112.410993. Epub 2012 Dec 3.

Abstract

The heme enzyme indoleamine 2,3-dioxygenase (IDO) is a key regulator of immune responses through catalyzing l-tryptophan (l-Trp) oxidation. Here, we show that hydrogen peroxide (H(2)O(2)) activates the peroxidase function of IDO to induce protein oxidation and inhibit dioxygenase activity. Exposure of IDO-expressing cells or recombinant human IDO (rIDO) to H(2)O(2) inhibited dioxygenase activity in a manner abrogated by l-Trp. Dioxygenase inhibition correlated with IDO-catalyzed H(2)O(2) consumption, compound I-mediated formation of protein-centered radicals, altered protein secondary structure, and opening of the distal heme pocket to promote nonproductive substrate binding; these changes were inhibited by l-Trp, the heme ligand cyanide, or free radical scavengers. Protection by l-Trp coincided with its oxidation into oxindolylalanine and kynurenine and the formation of a compound II-type ferryl-oxo heme. Physiological peroxidase substrates, ascorbate or tyrosine, enhanced rIDO-mediated H(2)O(2) consumption and attenuated H(2)O(2)-induced protein oxidation and dioxygenase inhibition. In the presence of H(2)O(2), rIDO catalytically consumed nitric oxide (NO) and utilized nitrite to promote 3-nitrotyrosine formation on IDO. The promotion of H(2)O(2) consumption by peroxidase substrates, NO consumption, and IDO nitration was inhibited by l-Trp. This study identifies IDO as a heme peroxidase that, in the absence of substrates, self-inactivates dioxygenase activity via compound I-initiated protein oxidation. l-Trp protects against dioxygenase inactivation by reacting with compound I and retarding compound II reduction to suppress peroxidase turnover. Peroxidase-mediated dioxygenase inactivation, NO consumption, or protein nitration may modulate the biological actions of IDO expressed in inflammatory tissues where the levels of H(2)O(2) and NO are elevated and l-Trp is low.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biocatalysis
  • Circular Dichroism
  • Escherichia coli / genetics
  • Heme / chemistry*
  • Heme / metabolism
  • Humans
  • Hydrogen Peroxide / chemistry*
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / chemistry*
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / metabolism
  • Kinetics
  • Nitric Oxide / chemistry
  • Oxidation-Reduction
  • Peroxidases / chemistry*
  • Peroxidases / metabolism
  • Protein Conformation
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Solutions
  • Spectrum Analysis, Raman

Substances

  • Indoleamine-Pyrrole 2,3,-Dioxygenase
  • Recombinant Proteins
  • Solutions
  • Nitric Oxide
  • Heme
  • Hydrogen Peroxide
  • Peroxidases