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Feline congenital erythropoietic porphyria: two homozygous UROS missense mutations cause the enzyme deficiency and porphyrin accumulation.

Abstract
The first feline model of human congenital erythropoietic porphyria (CEP) due to deficient uroporphyrinogen III synthase (URO-synthase) activity was identified by its characteristic clinical phenotype, and confirmed by biochemical and molecular genetic studies. The proband, an adult domestic shorthair cat, had dark-red urine and brownish discolored teeth with red fluorescence under ultraviolet light. Biochemical studies demonstrated markedly increased uroporphyrinogen I in urine and plasma (2,650- and 10,700-fold greater than wild type, respectively), whereas urinary 5-aminolevulinic acid and porphobilinogen were lower than normal. Erythrocytic URO-synthase activity was <1% of mean wild-type activity, confirming the diagnosis and distinguishing it from feline phenocopies having acute intermittent porphyria. Sequencing of the affected cat's UROS gene revealed two missense mutations, c.140C>T (p.S47F) in exon 3 and c.331G>A (p.G111S) in exon 6, both of which were homozygous, presumably owing to parental consanguinity. Neither was present in 100 normal cat alleles. Prokaryotic expression and thermostability studies of the purified monomeric wild-type, p.S47F, p.G111S, and p.S47F/G111S enzymes showed that the p.S47F enzyme had 100% of wild-type specific activity but ~50% decreased thermostability, whereas the p.G111S and p.S47F/G111S enzymes had about 60% and 20% of wild-type specific activity, respectively, and both were markedly thermolabile. Molecular modeling results indicated that the less active/less stable p.G111S enzyme was further functionally impaired by a structural interaction induced by the presence of the S47F substitution. Thus, the synergistic interaction of two rare amino acid substitutions in the URO-synthase polypeptide caused the feline model of human CEP.
AuthorsSonia Clavero, David F Bishop, Urs Giger, Mark E Haskins, Robert J Desnick
JournalMolecular medicine (Cambridge, Mass.) (Mol Med) 2010 Sep-Oct Vol. 16 Issue 9-10 Pg. 381-8 ISSN: 1528-3658 [Electronic] United States
PMID20485863 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
Chemical References
  • Mutant Proteins
  • Porphyrins
  • Uroporphyrinogen III Synthetase
Topics
  • Animals
  • Cat Diseases (blood, enzymology, genetics, urine)
  • Cats
  • Erythrocytes (metabolism)
  • Homozygote
  • Male
  • Models, Molecular
  • Molecular Sequence Data
  • Mutant Proteins (chemistry, genetics, metabolism)
  • Mutation, Missense (genetics)
  • Porphyria, Erythropoietic (blood, enzymology, urine, veterinary)
  • Porphyrins (blood, metabolism, urine)
  • Uroporphyrinogen III Synthetase (chemistry, genetics, metabolism)

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