Feline congenital erythropoietic porphyria: two homozygous UROS missense mutations cause the enzyme deficiency and porphyrin accumulation.
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.
Clavero
Sonia
S
Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York, NY, USA.
Bishop
David F
DF
Giger
Urs
U
Haskins
Mark E
ME
Desnick
Robert J
RJ
D000818:Animals; D002371:Cat Diseases / Q000097:blood / Q000201:enzymology* / Q000235:genetics* / Q000652:urine; D002415:Cats; D004912:Erythrocytes / Q000378:metabolism; D006720:Homozygote; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense / Q000235:genetics*; D017092:Porphyria, Erythropoietic / Q000097:blood / Q000201:enzymology / Q000652:urine / Q000662:veterinary*; D011166:Porphyrins / Q000097:blood / Q000378:metabolism* / Q000652:urine; D014576:Uroporphyrinogen III Synthetase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
D050505:Mutant Proteins; D011166:Porphyrins; D014576:Uroporphyrinogen III Synthetase