Eosinophil peroxidase

828813861ENSG00000121053ENSMUSG00000052234P11678P49290NM_000502NM_007946NP_000493NP_031972Eosinophil peroxidase is an enzyme found within the eosinophil granulocytes, innate immune cells of humans and mammals. This oxidoreductase protein is encoded by the gene EPX, expressed within these myeloid cells. EPO shares many similarities with its orthologous peroxidases, myeloperoxidase (MPO), lactoperoxidase (LPO), and thyroid peroxidase (TPO). The protein is concentrated in secretory granules within eosinophils. Eosinophil peroxidase is a heme peroxidase, its activities including the oxidation of halide ions to bacteriocidal reactive oxygen species, the cationic disruption of bacterial cell walls, and the post-translational modification of protein amino acid residues. Eosinophil peroxidase is an enzyme found within the eosinophil granulocytes, innate immune cells of humans and mammals. This oxidoreductase protein is encoded by the gene EPX, expressed within these myeloid cells. EPO shares many similarities with its orthologous peroxidases, myeloperoxidase (MPO), lactoperoxidase (LPO), and thyroid peroxidase (TPO). The protein is concentrated in secretory granules within eosinophils. Eosinophil peroxidase is a heme peroxidase, its activities including the oxidation of halide ions to bacteriocidal reactive oxygen species, the cationic disruption of bacterial cell walls, and the post-translational modification of protein amino acid residues. The major function of eosinophil peroxidase is to catalyze the formation of hypohalous acids from hydrogen peroxide and halide ions in solution. For example: Hypohalous acids formed from halides or pseudohalides are potent oxidizing agents. However, the role of eosinophilic peroxidase seems to be to generate hyphalous acids largely from bromide and iodide rather than chloride, since the former are favored greatly over the latter. The enzyme myeloperoxidase is responsible for formation of most of the hypochlorous acid in the body, and eosinophil peroxidase is responsible for reactions involving bromide and iodide. The open reading frame of human eosinophil peroxidase was found to have a length of 2,106 base pairs (bp). This comprises a 381-bp prosequence, a 333-bp sequence encoding the light chain and a 1,392-bp sequence encoding the heavy chain. In addition to these there is a 452-bp untranslated region at the 3' end containing the AATAAA polyadenylation signal. The promoter sequence for human eosinophil peroxidase is an unusually strong promoter. All the major regulatory elements are located within 100 bp upstream of the gene. The profile of EPX expression has been characterized and is available online via BioGPS. This dataset indicates that both in humans and mice, EPX is only expressed in the bone marrow. At this level, it is more than 30 times the average level of expression over all tissues in the body. The polypeptide chain is processed proteolytically into a heavy and a light chain during maturation. However, the two chains are still intimately connected not least of all by the covalently linked heme cofactor. The protein is produced on ribosomes embedded on the surface of the endoplasmic reticulum, since it must be ultimately localized to the granules.The precursor protein goes through the following processing steps before becoming active: Unlike MPO, heme in EPO is not linked via methionine. This affects the catalytic characteristics (see Active site). Eosinophil peroxidase is a predominately α-helical heme-containing enzyme. The core of the catalytic domain surrounding the active site consists of six α-helices, five from the heavy polypeptide chain and one from the light. The fold of the enzyme is known as the heme peroxidase fold, conserved among all members of this gene family. However, not all members possess peroxidase activity.