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

• Published in: The Journal of biological chemistry 2013-01, Vol.288 (3), p.1548-1567
• Main Authors: Freewan, Mohammed, Rees, Martin D, Plaza, Tito S Sempértegui, Glaros, Elias, Lim, Yean J, Wang, Xiao Suo, Yeung, Amanda W S, Witting, Paul K, Terentis, Andrew C, Thomas, Shane R
• Format: Article
• Language: English
• Subjects: Biocatalysis; Circular Dichroism; Enzymology; 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
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.410993

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.