2aex | pdb_00002aex
The 1.58A Crystal Structure of Human Coproporphyrinogen Oxidase Reveals the Structural Basis of Hereditary Coproporphyria
Structural highlights
DiseaseHEM6_HUMAN Defects in CPOX are the cause of hereditary coproporphyria (HCP) [MIM:121300. HCP is an acute hepatic porphyria and an autosomal dominant disease characterized by neuropsychiatric disturbances and skin photosensitivity. Biochemically, there is an overexcretion of coproporphyrin III in the urine and in the feces. HCP is clinically characterized by attacks of abdominal pain, neurological disturbances, and psychiatric symptoms. The symptoms are generally manifested with rapid onset, and can be precipitated by drugs, alcohol, caloric deprivation, infection, endocrine factors or stress. A severe variant form is harderoporphyria, which is characterized by earlier onset attacks, massive excretion of harderoporphyrin in the feces, and a marked decrease of coproporphyrinogen IX oxidase activity.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] FunctionHEM6_HUMAN Key enzyme in heme biosynthesis. Catalyzes the oxidative decarboxylation of propionic acid side chains of rings A and B of coproporphyrinogen III. 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 PubMedHereditary coproporphyria is an autosomal dominant disorder resulting from the half-normal activity of coproporphyrinogen oxidase (CPO), a mitochondrial enzyme catalyzing the antepenultimate step in heme biosynthesis. The mechanism by which CPO catalyzes oxidative decarboxylation, in an extraordinary metal- and cofactor-independent manner, is poorly understood. Here, we report the crystal structure of human CPO at 1.58-A resolution. The structure reveals a previously uncharacterized tertiary topology comprising an unusually flat seven-stranded beta-sheet sandwiched by alpha-helices. In the biologically active dimer (K(D) = 5 x 10(-7) M), one monomer rotates relative to the second by approximately 40 degrees to create an intersubunit interface in close proximity to two independent enzymatic sites. The unexpected finding of citrate at the active site allows us to assign Ser-244, His-258, Asn-260, Arg-262, Asp-282, and Arg-332 as residues mediating substrate recognition and decarboxylation. We favor a mechanism in which oxygen serves as the immediate electron acceptor, and a substrate radical or a carbanion with substantial radical character participates in catalysis. Although several mutations in the CPO gene have been described, the molecular basis for how these alterations diminish enzyme activity is unknown. We show that deletion of residues (392-418) encoded by exon six disrupts dimerization. Conversely, harderoporphyria-causing K404E mutation precludes a type I beta-turn from retaining the substrate for the second decarboxylation cycle. Together, these findings resolve several questions regarding CPO catalysis and provide insights into hereditary coproporphyria. Structural basis of hereditary coproporphyria.,Lee DS, Flachsova E, Bodnarova M, Demeler B, Martasek P, Raman CS Proc Natl Acad Sci U S A. 2005 Oct 4;102(40):14232-7. Epub 2005 Sep 21. PMID:16176984[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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