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1jr2
From Proteopedia
Structure of Uroporphyrinogen III Synthase
Structural highlights
Disease[HEM4_HUMAN] Defects in UROS are the cause of congenital erythropoietic porphyria (CEP) [MIM:263700]; also known as Gunther disease. Porphyrias are inherited defects in the biosynthesis of heme, resulting in the accumulation and increased excretion of porphyrins or porphyrin precursors. They are classified as erythropoietic or hepatic, depending on whether the enzyme deficiency occurs in red blood cells or in the liver. The manifestations of CEP are heterogeneous, ranging from nonimmune hydrops fetalis due to severe hemolytic anemia in utero to milder, later onset forms, which have only skin lesions due to cutaneous photosensitivity in adult life. The deficiency in UROS activity results in the non-enzymatic conversion of hydroxymethylbilane (HMB) into the uroporphyrinogen-I isomer.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] Note=Severe congenital erythropoietic porphyria is associated with non-immune hydrops fetalis, a generalized edema of the fetus with fluid accumulation in the body cavities due to non-immune causes. Non-immune hydrops fetalis is not a diagnosis in itself but a symptom, a feature of many genetic disorders, and the end-stage of a wide variety of disorders. Function[HEM4_HUMAN] Catalyzes cyclization of the linear tetrapyrrole, hydroxymethylbilane, to the macrocyclic uroporphyrinogen III, the branch point for the various sub-pathways leading to the wide diversity of porphyrins. Porphyrins act as cofactors for a multitude of enzymes that perform a variety of processes within the cell such as methionine synthesis (vitamin B12) or oxygen transport (heme). Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedUroporphyrinogen III synthase, U3S, the fourth enzyme in the porphyrin biosynthetic pathway, catalyzes cyclization of the linear tetrapyrrole, hydroxymethylbilane, to the macrocyclic uroporphyrino gen III, which is used in several different pathways to form heme, siroheme, chlorophyll, F(430) and vitamin B(12). U3S activity is essential in all organisms, and decreased activity in humans leads to the autosomal recessive disorder congenital erythropoetic porphyria. We have determined the crystal structure of recombinant human U3S at 1.85 A resolution. The protein folds into two alpha/beta domains connected by a beta-ladder. The active site appears to be located between the domains, and variations in relative domain positions observed between crystallographically independent molecules indicates the presence of flexibility that may be important in the catalytic cycle. Possible mechanisms of catalysis were probed by mutating each of the four invariant residues in the protein that have titratable side chains. Additionally, six other highly conserved and titratable side chains were also mutated. In no case, however, did one of these mutations abolish enzyme activity, suggesting that the mechanism does not require acid/base catalysis. Crystal structure of human uroporphyrinogen III synthase.,Mathews MA, Schubert HL, Whitby FG, Alexander KJ, Schadick K, Bergonia HA, Phillips JD, Hill CP EMBO J. 2001 Nov 1;20(21):5832-9. PMID:11689424[14] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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