Factors determining the sequence of oxidative decarboxylation of the 2- and 4-propionate substituents of coproporphyrinogen III by coproporphyrinogen oxidase in rat liver

Elder, George H.; Evans, James O.; Jackson, Jeffrey R.; Jackson, Anthony H.

doi:10.1042/bj1690215

Cited by 53 publications

(28 citation statements)

References 24 publications

(31 reference statements)

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“…(A) Reaction catalyzed by CPO involves both oxidation and decarboxylation (5). CPO sequentially decarboxylates (26,30) the propionates attached to A and B rings without affecting those on C and D rings. A hydrogen atom from the ␤-position of the propionate side chain also is removed at each step (31,32).…”

Section: Resultsmentioning

confidence: 99%

Structural basis of hereditary coproporphyria

Lee

Flachsová

Bodnárová

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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Hereditary 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 metaland cofactor-independent manner, is poorly understood. Here, we report the crystal structure of human CPO at 1.58-Å resolution. The structure reveals a previously uncharacterized tertiary topology comprising an unusually flat seven-stranded ␤-sheet sandwiched by ␣-helices. In the biologically active dimer (KD ‫؍‬ 5 ؋ 10 ؊7 M), one monomer rotates relative to the second by Ϸ40°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 ␤-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.coproporphyrinogen oxidase ͉ oxidative decarboxylation ͉ mitochondria ͉ x-ray crystallography T he terminal three steps of heme biosynthesis occur within the mitochondria (1, 2). First, coproporphyrinogen III is converted to protoporphyrinogen IX in the intermembrane space (3, 4) by coproporphyrinogen oxidase (CPO) (5, 6). Thus, CPO contains an unusually long (110 residues) N-terminal targeting sequence, required for its import into the mitochondria (7,8). The substrate for CPO is generated in the cytosol (9) by uroporphyrinogen decarboxylase, and the precise mechanism by which it enters the mitochondria remains to be elucidated. Second, protoporphyrinogen oxidase mediates the six electron oxidation of protoporphyrinogen to protoporphyrin IX. This enzyme is localized to the cytoplasmic side of the inner mitochondrial membrane. Third, ferrochelatase inserts the ferrous iron to generate heme within the matrix of the mitochondria. Hence, the heme biosynthetic pathway is not only partitioned between mitochondria and cytosol, but the last three enzymes are compartmentalized within the mitochondria.Partial deficiency of CPO leads to hereditary coproporphyria (HCP), an acute hepatic porphyria inherited in an autosomal dominant fashion (10-12). The disease is characterized by abdominal pain, neuropsychiatric symptoms, and͞or cutaneous photosensitivity (13). If diagnosed early, HCP can be treat...

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Section: Resultsmentioning

confidence: 99%

Structural basis of hereditary coproporphyria

Lee

Flachsová

Bodnárová

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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“…If the reaction intermediate is able to reposition within the active-site cavity, this architecture would explain why the first decarboxylation, on the pyrrole A ring, is rate-limiting and rapidly followed by decarboxylation of the pyrrole B ring propionate (13,14). One potential advantage of the substrateinduced conformational change is that it might generate a specific pathway and binding site for the molecular oxygen cofactor, such as seen for cholesterol oxidase (42,43).…”

Section: Odcpo/hem13p Structurementioning

confidence: 99%

“…There are reports of requirements for copper (8) and manganese (9), although other studies found no metal ion or other cofactor dependence (except O 2 ) for odCPO activity (10 -12). Regardless of mechanistic details, the first decarboxylation has been shown to be the rate-limiting step for the overall reaction, and transient formation of the 3-carboxyl intermediate harderoporphyrinogen has been demonstrated (13,14).…”

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confidence: 99%

Crystal Structure of the Oxygen-dependant Coproporphyrinogen Oxidase (Hem13p) of Saccharomyces cerevisiae

Phillips¹,

Whitby

Warby³

et al. 2004

Journal of Biological Chemistry

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Coproporphyrinogen oxidase (CPO) is an essential enzyme that catalyzes the sixth step of the heme biosynthetic pathway. Unusually for heme biosynthetic enzymes, CPO exists in two evolutionarily and mechanistically distinct families, with eukaryotes and some prokaryotes employing members of the highly conserved oxygen-dependent CPO family. Here, we report the crystal structure of the oxygen-dependent CPO from Saccharomyces cerevisiae (Hem13p), which was determined by optimized sulfur anomalous scattering and refined to a resolution of 2.0 Å. The protein adopts a novel structure that is quite different from predicted models and features a central flat seven-stranded antiparallel sheet that is flanked by helices. The dimeric assembly, which is seen in different crystal forms, is formed by packing of helices and a short isolated strand that forms a ␤-ladder with its counterpart in the partner subunit. The deep active-site cleft is lined by conserved residues and has been captured in open and closed conformations in two different crystal forms. A substratesized cavity is completely buried in the closed conformation by the ϳ8-Å movement of a helix that forms a lid over the active site. The structure therefore suggests residues that likely play critical roles in catalysis and explains the deleterious effect of many of the mutations associated with the disease hereditary coproporphyria.

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“…Harderoporphyrinogen is the natural intermediate between copro-and protoporphyrinogen. Isoharderoporphyrinogen (vinyl group on pyrrole B instead of pyrrole A) has not been isolated from tissues synthesizing protoporphyrin IX; however, isoharderoporphyrinogen is a known substrate of coproporphyrinogen oxidase (17). Me, methyl (-CH3); Pr, propionyl (-CH2-CH2-COOH); V, vinyl (-CH=CH2).…”

Section: Introductionmentioning

confidence: 99%

Harderoporphyria: a variant hereditary coproporphyria.

Nordmann¹,

Grandchamp²,

H³

et al. 1983

J. Clin. Invest.

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A B S T R A C T Three siblings with intense jaundice and hemolytic anemia at birth were found to excrete a high level of coproporphyrin in their urine and feces; the pattern of fecal porphyrin excretion was atypical for hereditary coproporphyria because the major porphyrin was harderoporphyrin (>60%; normal value is <20%). The lymphocyte coproporphyrinogen III oxidase activity of each patient was 10% of control values, which suggests a homozygous state. Both parents showed only mild abnormalities in porphyrin excretion and lymphocyte coproporphyrinogen III oxidase activity decreased to 50% of normal values, as is expected in heterozygous cases of hereditary coproporphyria. Kinetic parameters of coproporphyrinogen III oxidase from these patients were clearly modified, with a Michaelis constant 15-20-fold higher than normal values when using coproporphyrinogen or harderoporphyrinogen as substrates. Maximal velocity was half the normal value, and we also observed a marked sensitivity to thermal denaturation. The possibility that a mutation affecting the enzyme on the active center which is specifically involved in the second decarboxylation (from harderoporphyrinogen to protoporphyrinogen) was eliminated by experiments on rat liver that showed that coproporphyrinogen and harderoporphyrinogen were metabolized at the same active center. The pattern of porphyrin excretion and the coproporphyrinogen oxidase from the three patients exhibited abnormalities that were different from the abnormalities found in another recently described homozygous case of hereditary coproporphyria. We suggest naming this variant of coproporphyrinogen oxidase defect "harderoporphyria."

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Factors determining the sequence of oxidative decarboxylation of the 2- and 4-propionate substituents of coproporphyrinogen III by coproporphyrinogen oxidase in rat liver

Cited by 53 publications

References 24 publications

Structural basis of hereditary coproporphyria

Structural basis of hereditary coproporphyria

Crystal Structure of the Oxygen-dependant Coproporphyrinogen Oxidase (Hem13p) of Saccharomyces cerevisiae

Harderoporphyria: a variant hereditary coproporphyria.

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