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An unusual insertion/deletion in the gene encoding the beta-subunit of propionyl-CoA carboxylase is a frequent mutation in Caucasian propionic acidemia.

ABSTRACT: Propionic acidemia is an inherited disorder of organic acid metabolism that is caused by deficiency of propionyl-CoA carboxylase (PCC; EC 6.4.1.3). Affected patients fall into two complementation groups, pccA and pccBC (subgroups B, C, and BC), resulting from deficiency of the nonidentical alpha and beta subunits of PCC, respectively. We have detected an unusual insertion/deletion in the DNA of patients from the pccBC and pccC subgroups that replaces 14 nucleotides in the coding sequence of the beta subunit with 12 nucleotides unrelated to this region of the gene. This results in elimination of an Msp I restriction site, a 2-base-pair (bp) deletion, a frameshift, and a stop codon in the new frame approximately 100 amino acid residues proximal to the normal carboxyl terminus. Among 14 unrelated Caucasian patients in the pccBC complementation group, this unique mutation was found in 8 of 28 mutant alleles examined. Mutant allele-specific oligonucleotide hybridization to amplified genomic DNAs revealed that the inserted 12 nucleotides do not originate in an approximately 1000-bp region around the mutation. In the course of our investigation, we identified another mutation in the same exon: a 3-bp in-frame deletion that eliminates one of two isoleucine codons immediately preceding the Msp I site. Two unrelated patients were compound heterozygotes for this single-codon deletion and for the insertion/deletion described above. We conclude that either there is a propensity for the PCC beta-subunit gene to undergo mutations of this sort at this position or, more likely, the mutations in all of the involved Caucasian patients have a common origin in preceding generations.

SUBMITTER: Tahara T

PROVIDER: S-EPMC53477 | biostudies-other | 1990 Feb

REPOSITORIES: biostudies-other

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An unusual insertion/deletion in the gene encoding the beta-subunit of propionyl-CoA carboxylase is a frequent mutation in Caucasian propionic acidemia.

Tahara T T Kraus J P JP Rosenberg L E LE

Proceedings of the National Academy of Sciences of the United States of America 19900201 4

Propionic acidemia is an inherited disorder of organic acid metabolism that is caused by deficiency of propionyl-CoA carboxylase (PCC; EC 6.4.1.3). Affected patients fall into two complementation groups, pccA and pccBC (subgroups B, C, and BC), resulting from deficiency of the nonidentical alpha and beta subunits of PCC, respectively. We have detected an unusual insertion/deletion in the DNA of patients from the pccBC and pccC subgroups that replaces 14 nucleotides in the coding sequence of the ...[more]

PMID: 2154743

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Project description:The pathway of autotrophic CO2 fixation was studied in the phototrophic bacterium Chloroflexus aurantiacus and in the aerobic thermoacidophilic archaeon Metallosphaera sedula. In both organisms, none of the key enzymes of the reductive pentose phosphate cycle, the reductive citric acid cycle, and the reductive acetyl coenzyme A (acetyl-CoA) pathway were detectable. However, cells contained the biotin-dependent acetyl-CoA carboxylase and propionyl-CoA carboxylase as well as phosphoenolpyruvate carboxylase. The specific enzyme activities of the carboxylases were high enough to explain the autotrophic growth rate via the 3-hydroxypropionate cycle. Extracts catalyzed the CO2-, MgATP-, and NADPH-dependent conversion of acetyl-CoA to 3-hydroxypropionate via malonyl-CoA and the conversion of this intermediate to succinate via propionyl-CoA. The labelled intermediates were detected in vitro with either 14CO2 or [14C]acetyl-CoA as precursor. These reactions are part of the 3-hydroxypropionate cycle, the autotrophic pathway proposed for C. aurantiacus. The investigation was extended to the autotrophic archaea Sulfolobus metallicus and Acidianus infernus, which showed acetyl-CoA and propionyl-CoA carboxylase activities in extracts of autotrophically grown cells. Acetyl-CoA carboxylase activity is unexpected in archaea since they do not contain fatty acids in their membranes. These aerobic archaea, as well as C. aurantiacus, were screened for biotin-containing proteins by the avidin-peroxidase test. They contained large amounts of a small biotin-carrying protein, which is most likely part of the acetyl-CoA and propionyl-CoA carboxylases. Other archaea reported to use one of the other known autotrophic pathways lacked such small biotin-containing proteins. These findings suggest that the aerobic autotrophic archaea M. sedula, S. metallicus, and A. infernus use a yet-to-be-defined 3-hydroxypropionate cycle for their autotrophic growth. Acetyl-CoA carboxylase and propionyl-CoA carboxylase are proposed to be the main CO2 fixation enzymes, and phosphoenolpyruvate carboxylase may have an anaplerotic function. The results also provide further support for the occurrence of the 3-hydroxypropionate cycle in C. aurantiacus.

Project description:Propionic acidemia is a rare metabolic disorder caused by a deficiency of propionyl- CoA carboxylase, the enzyme converting propionyl-CoA to methylmalonyl-CoA that subsequently enters the citric acid cycle as succinyl-CoA. Patients with propionic acidemia cannot metabolize propionic acid, which combines with oxaloacetate to form methylcitric acid. This, with the defective supply of succinyl-CoA, may lead to a deficiency in citric acid cycle intermediates.The objective of this study was to determine whether supplements with glutamine (400mg/kg per day), citrate (7.5mEq/kg per day), or ornithine ?-ketoglutarate (400mg/kg per day) (anaplerotic agents that could fill up the citric acid cycle) would affect plasma levels of glutamine and ammonia, the urinary excretion of Krebs cycle intermediates, and the clinical outcome in 3 patients with propionic acidemia.Each supplement was administered daily for four weeks with a two week washout period between supplements. The supplement that produced the most favorable changes was supplemented for 30 weeks following the initial study period and then for a 2 year extension.The urinary excretion of the Krebs cycle intermediates, ?-ketoglutarate, succinate, and fumarate increased significantly compared to baseline during citrate supplementation, but not with the other two supplements. For this reason, citrate supplements were continued in the second part of the study. The urinary excretion of methylcitric acid and 3-hydroxypropionic acid did not change with any intervention. No significant changes in ammonia or glutamine levels were observed with any supplement. However, supplementation with any anaplerotic agents normalized the physiological buffering of ammonia by glutamate, with plasma glutamate and alanine levels significantly increasing, rather than decreasing with increasing ammonia levels. No significant side effects were observed with any therapy and safety labs (blood counts, chemistry and thyroid profile) remained unchanged. Motor and cognitive development was severely delayed before the trial and did not change significantly with therapy. Hospitalizations per year did not change during the trial period, but decreased significantly (p<0.05) in the 2years following the study (when citrate was continued) compared to the 2years before and during the study.These results indicate that citrate entered the Krebs cycle providing successful anaplerotic therapy by increasing levels of the downstream intermediates of the Krebs cycle: ?-ketoglutarate, succinate and fumarate. Citrate supplements were safe and might have contributed to reduce hospitalizations in patients with propionic acidemia.

Dataset Information

An unusual insertion/deletion in the gene encoding the beta-subunit of propionyl-CoA carboxylase is a frequent mutation in Caucasian propionic acidemia.

Publications

An unusual insertion/deletion in the gene encoding the beta-subunit of propionyl-CoA carboxylase is a frequent mutation in Caucasian propionic acidemia.

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