IDO2/INDOL1 [MD232]

Indolamine-2,3-dioxygenase 2 (IDO2) is a presumptive immunomodulatory gene based on its close structural relationship to IDO1 and its expression in a variety of antigen-presenting cell types. IDO2 is also known as INDOL1 (indoleamine 2,3-dioxygenase-like protein 1) and is a 407 amino acid protein that is expressed in various tissues, including liver, small intestine, spleen, placenta, thymus, lung, brain, kidney, colon and dendritic cells. It is one of three enzymes that catalyze the first and rate-limiting step in the kynurenine pathway, the O2-dependent oxidation of L-tryptophan to N-formylkynurenine, the others being Indoleamine-pyrrole 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO). IDO2 is selectively inhibited by D-1MT (1-methyl-d-tryptophan), which also inhibits IDO and is significant because IDO expression causes suppression of T cell responses to tumors in dendritic cells. The inhibition of IDO2 by D-1MT suggests a common function in immunomodulation. In the human IDO2 gene, two single nucleotide polymorphisms have been detected which abolish the enzymatic function of IDO2.