Porphobilinogen-synthase (delta-aminolevulinic acid dehydratase) deficiency in bone marrow cells of two patients with porphobilinogen-synthase defect acute porphyria

Co-synthesis of Human delta-Aminolevulinate Dehydratase (ALAD) Mutants with the Wild-type Enzyme in Cell-free System-Critical Importance of Conformation on Enzyme Activity-

Properties of mutant delta-aminolevulinate dehydratase (ALAD) found in patients with ALAD porphyria were studied by enzymological and immunological analyses after the synthesis of enzyme complexes using a cell-free system. Enzyme activities of homozygous G133R, K59N/G133R, V153M, and E89K mutants were 11%, 22%, 67%, and 75% of the wild-type ALAD, respectively, whereas that of K59N, a normal variant, was 112%. Enzyme activities of L273R, C132R and F12L were undetectable. Co-synthesis of F12L, L273R, G133R, K59N/G133R, or C132R mutants with the wild-type at various ratios showed that ALAD activity was proportionally decreased in the amount of the wild-type in the complex. In contrast, co-synthesis of V153M, K59N, and E89K with the wild-type did not influence enzyme activity of the wild-type. Surface charge changes in K59N, E89K, C132R and G133R predicted by mutations were also confirmed by native polyacrylamide gel electrophoresis. A compound E89K and C132R complex showed ALAD activity similar to that was found in erythrocytes of the patient. These findings indicate that cell-free synthesis of ALAD proteins reflects enzymatic activities found in patients, and suggest that, in addition to the direct effect of mutations on the catalytic activity, conformational effects play an important role in determining enzyme activity.

delta-Aminolevulinate dehydratase (ALAD) porphyria: the first case in North America with two novel ALAD mutations

The molecular basis of the enzymatic defect responsible for delta-aminolevulinate dehydratase (ALAD) porphyria (ADP) was investigated in a 14-year-old male who presented clinical and laboratory findings typical of ADP. Nucleotide sequence analysis of ALAD cDNAs from the proband revealed two novel mutations, a 265G to A base transition (C1) and a 394C to T base transition (C2), resulting in amino acid substitutions, Glu89Lys and Cys132Arg, respectively. Both mutations were present within exon 5 of the ALAD gene, and appeared to influence the binding of zinc to the enzyme which is essential for enzyme activity. It was found that the C1 mutation was inherited from his father, while the C2 mutation was from his mother. Expression of these mutant ALAD cDNAs in Chinese hamster ovary cells produced normal ALAD mRNA levels, but markedly decreased ALAD protein and enzyme activity. These results suggest that the combination of the two aberrant ALADs with little enzyme activity accounts for the markedly decreased ALAD activity observed in the proband. This case represents the molecular analysis of the ALAD gene defects in the first case of ADP identified in North America, who is a compound heterozygote for two novel ALAD gene defects.

Novel molecular defects of the delta-aminolevulinate dehydratase gene in a patient with inherited acute hepatic porphyria

Cloning and expression of the defective gene for delta-aminolevulinate dehydratase (ALAD) from the second of 2 German patients with ALAD deficiency porphyria (ADP), who had been originally reported by Doss et al. in 1979, were performed. Cloning of cDNAs for the defective ALAD were performed using Epstein-Barr virus (EBV)-transformed lymphoblastoid cells of the proband, and nucleotide sequences of cloned cDNA were determined. Two separate mutations of ALAD cDNA were identified in each ALAD allele. One was G457A, termed "H1," resulting in V153M substitution, while the other was a deletion of 2 sequential bases at T(818) and C(819), termed "H2," resulting in a frame shift with a premature stop codon at the amino acid position of 294. Using allele-specific oligonucleotide hybridization, the mother of the proband was shown to have an H1 defect, while using genomic DNA analysis, the father was shown to have an H2 defect. Expression of H1 cDNA in Chinese hamster ovary cells produced an ALAD protein with only a partial activity (10.65% +/- 1.80% of the normal), while H2 cDNA encoded no significant protein. These data thus demonstrate that the proband was associated with 2 novel molecular defects of the ALAD gene, 1 in each allele, and account for the extremely low ALAD activity in his erythrocytes ( approximately 1% of normal).