S. Lancellotti, L. Novarese and R. De Cristofaro Pages 2205 - 2214 ( 10 )
The enzyme indoleamine 2,3-dioxygenase (IDO, EC 1.13.11.42) belongs to the family of heme-containing oxidoreductases and catalyzes the first and rate-limiting step in the kynurenine pathway, the major pathway of tryptophan metabolism. IDO is folded into one large and one small distinct α-helical domains, with the heme prosthetic ring positioned between them. The enzyme, through the oxidative properties of the Fe3+ atom present at the centre of the heme ring, catalyses the oxidative cleavage of the pyrrole ring of L-Trp to generate N-formyl-kynurenine. The active IDO conformer exists only in the presence of reducing cofactors (such as cytochrome b5), requiring the single electron reduction of ferric-to-ferrous iron (Fe3+ Fe2+), which facilitates binding of L-Trp and O2 to the enzyme active site. IDO, through production of kynurenine and other downstream metabolites, can regulate immune responses, suppressing effector T-cell function and favouring the differentiation of regulatory T cells. Local expression of the enzyme during inflammation is another self-protection mechanism, which limits antigen-specific immune responses, especially in some organs, as the central nervous system. The detailed knowledge of the structural and functional properties of IDO, was a fundamental step to design and develop new molecules for the pharmacological inhibition of IDO activity in several clinical settings.
Indoleamine 2,3-dioxygenase,Immune tolerance,X-ray structure of oxygenases,enzyme,heme-containing oxidoreductases,kynurenine,tryptophan metabolism,helical domains,N-formyl-kynurenine,IDO
, , Department of Internal Medicine&Geriatrics, Haemostasis Research Center, Catholic University School of Medicine,Largo Francesco Vito, 1, 00168 Rome, Italy.