Mechanism and sterochemistry of vinyl group formation in haem biosynthesis

Zaman, Zahur; Abboud, Muayad M.; Akhtar, M.

doi:10.1039/c39720001263

Cited by 20 publications

(6 citation statements)

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“…It is well established that CPO abstracts the pro-S hydrogen from the methylene group adjacent to the pyrrole ring (Fig. 1 A), leading to the generation of a vinyl group from the remaining three hydrogens and two carbons without rearrangement (31,32). Such strong stereoselectivity indicates that CPO strictly constrains the orientation of the substrate in the active site, and our structure provides insights into how this result can be achieved (vide supra).…”

Section: Cpo Structure Lacks a Transition Metal Centermentioning

confidence: 92%

“…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). The chemical identity of the oxidation end product(s) remains to be elucidated.…”

Section: Resultsmentioning

confidence: 99%

“…1A) without using metals (25,27,35), reducing agents, thiols, prosthetic groups, organic cofactors, or modified amino acids (36). Whereas the stereochemistry of this reaction has been worked out (31,32), the molecular oxygen consumption presents an interesting mechanistic puzzle. From a clinical standpoint, a well defined correlation between the genotype and severity of disease is lacking (34).…”

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confidence: 99%

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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: Cpo Structure Lacks a Transition Metal Centermentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Structural basis of hereditary coproporphyria

Lee

Flachsová

Bodnárová

et al. 2005

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

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“…Studies of the mechanism offormation of the vinyl groups of protoporphyrinogen IX support the first of these alternatives. Thus stereospecific loss of a hydrogen atom from the 8methylene group of the propionate side chain and decarboxylation is believed to occur simultaneously (Zaman et al, 1972;Battersby et al, 1972;Jackson et al, 1974). Since the 2-propionate substituent is decarboxylated before the 4-propionate, this type of mechanism must lead to formation of harderoporphyrinogen as the intermediate.…”

Section: Nature Of the Sequential Decarboxylation Process Time Coursementioning

confidence: 99%

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

Elder¹,

Evans²,

Jackson

et al. 1978

Biochemical Journal

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Coproporphyrinogen oxidase (EC 1.3.3.3) catalyses the oxidative decarboxylation of the 2- and 4-propionate substituents of coproporphyrinogen III to form protoporphyrinogen IX. A 4-propionate-substituted porphyrinogen, harderoporphyrinogen, which is also a substrate for coproporphyrinogen oxidase, is formed during the reaction. Synthetic [(14)C]coproporphyrinogens III, specifically labelled in the carboxyl carbon atoms of either the 2- or 4-propionate substituents, were used to measure the rate of decarboxylation of each substituent by rat liver coproporphyrinogen oxidase. The experimental results, together with the recognition that in all known substrates of coproporphyrinogen oxidase only those propionate groups flanked by a specific arrangement of substituents are decarboxylated, indicate that the 4-propionate group of coproporphyrinogen III cannot be attacked until the 2-propionate group has been decarboxylated. Production of (14)CO(2) from the substrate labelled in the 2-propionate group therefore measures the formation of harderoporphyrinogen, whereas (14)CO(2) from the 4-propionate-labelled substrate measures protoporphyrinogen IX formation. The rate of harderoporphyrinogen formation is about twice that of protoporphyrinogen, and this ratio is unchanged by varying the concentration of coproporphyrinogen III or by competitive inhibition of the enzyme. When coproporphyrinogen III is present in an excess, two fractions of harderoporphyrinogen can be distinguished. One accumulates during the reaction, and the other, which is destined to become protoporphyrinogen IX, does not equilibrate with added harderoporphyrinogen. It is suggested that both decarboxylations take place at the same active centre, which becomes temporarily inaccessible to coproporphyrinogen III and added harderoporphyrinogen, and that the molecule rotates after the first decarboxylation to allow the second to take place.

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“…66.5-67. 5 2-Benzyloxycarbonyf-4-( 3 -methoxycarbonylpropyl)-3-methylpyrrole-5-carbox~~lic Acid.-The pyrrole (16) (9.9 g) in dry tetrahydrofuran (300 ml) was treated with sulphuryl chloride (16.2 g) in dry tetrahydrofuran (50 ml) and the solution was heated under reflux for 30 min and then evaporated. The resulting oil was poured into water-acetone (1 : 4; 2 000 ml) and boiled for 20 min after which sodium acetate (15 g) was added and the solution was stirred and heated for a further 20 min.…”

Section: Benzjll 3-(3-methou~carbon~lpr~py/)-24-dimethylp~~rrole-5-mentioning

confidence: 99%