Pyruvate dehydrogenase (lipoamide) alpha 1

The PDHA1 gene has about 17 kilobase pairs; it contains 11 exons, which range from 61 to 174 base pairs, and introns, whose sizes range from 600 base pairs to 5.7 kilobase pairs. The splice donor and acceptor sites present within the gene all conform to GT/AC rule of splicing. The DNA sequence in the transcription initiation site is very GC-rich. There is a "TATA box"-like sequence and a "CAAT present upstream from the cap site. There are also several sets of repeats, sequences resembling the Sp1 transcription factor binding site, and two cAMP receptor binding sites upstream of the cap.[6]

The preliminary peptide encoded by this gene was 29 amino acids at the very start of the sequence that correspond to a typical mitochondrial targeting leader sequence. The remaining 361 amino acids, starting at the N terminus with phenylalanine, represent the mature mitochondrial E1 alpha peptide.[7] Two of these mature PDHA proteins come together with two PDHB proteins to form a heterotetrameric E1 subunit. Crystal Structures allowed for a model in which the enzyme undergoes a 2-A shuttle-like motion of its heterodimers to perform the catalysis.[8] The protein encoded by the human PDHA1 gene is part of the pyruvate dehydrogenase multienzyme complex. The entire human complex is 9.5 MDa in size, and has been described as 60-meric, meaning there are over 60 components that are assembled to make the entire complex. These subunits are conserved across many species, as the function of this complex is essential for the generation of ATP for all eukaryotes.[9] Each component is responsible for the catalysis of one step in this pathway; this complex exists for the purpose of channeling the intermediates of each reaction to the next enzyme, thus greatly increasing the rate of reaction.[10]

The pyruvate dehydrogenase complex is responsible for the oxidative decarboxylation of pyruvate, with the final product being Acetyl CoA. Overall the complex catalyzes five reactions, with the overall reaction being:

Pyruvate + CoA + NAD⁺ → acetyl-CoA + CO₂

There are three different coenzymes required throughout the 5 steps that this complex carries out: thiamine pyrophosphate (TPP), lipoamide, and coenzyme A. This step is only one of the central metabolic pathway carried out by eukaryotes, in which glucose is oxidized to form carbon dioxide, water, and ATP. The E1 complex specifically uses the TPP cofactor to cleave the Calpha-C(=O) bond of pyruvate, and then transfer the acetyl group to the TPP coenzyme, thus resulting in an intermediate, hydroxylethyl-Tpp*E1, and producing CO₂. The thiazolium ring on the TPP is ideal for adding to carbonyl groups and acting as an electron sink, or a group that can pull electrons from a reaction and stabilize an electron-deficient intermediate.[10]

At least 71 disease-causing mutations in this gene have been discovered.[16] Mutations in the PDHA1 gene have been known to cause one form of pyruvate dehydrogenase deficiency. Pyruvate dehydrogenase deficiency is characterized by the buildup of a chemical called lactic acid in the body and a variety of neurological problems. Signs and symptoms of this condition usually first appear shortly after birth, and they can vary widely among affected individuals. The most common feature is a potentially life-threatening buildup of lactic acid (lactic acidosis), which can cause nausea, vomiting, severe breathing problems, and an abnormal heartbeat. People with pyruvate dehydrogenase deficiency usually have neurological problems as well. Most have delayed development of mental abilities and motor skills such as sitting and walking. Other neurological problems can include intellectual disability, seizures, weak muscle tone (hypotonia), poor coordination, and difficulty walking. Some affected individuals have abnormal brain structures, such as underdevelopment of the tissue connecting the left and right halves of the brain (corpus callosum), wasting away (atrophy) of the exterior part of the brain known as the cerebral cortex, or patches of damaged tissue (lesions) on some parts of the brain. Because of the severe health effects, many individuals with pyruvate dehydrogenase deficiency do not survive past childhood, although some may live into adolescence or adulthood.[5] Most cases result from mutations in this gene, and countless types of mutations have been identified. The mutations in this gene range from missense mutations, in which one nucleotide is substituted, to much larger deletions of many nucleotide base pairs.[17][18][19]

While most of the clinical presentation is homogenous with the general disease, some cases have been identified in which there was focal dilatation of the right lateral ventricle with unilateral periventricular leukomalacia (PVL) with subependymal cyst.[20]

In women, this deficiency can be much harder to detect. This is because of the chance that there will be a skewed X inactivation pattern enzyme measurement in fibroblasts, meaning that the enzyme activity measurement may not be entirely accurate. Because the clinical presentation of this disorder overlaps heavily with deficiencies in oxidative phosphorylation, it is recommended to perform a detailed biochemical analysis on a muscle biopsy in females with a suspected pyruvate dehydrogenase deficiency, followed by molecular genetic analysis of the PDHA1 gene.[21]

Click on genes, proteins and metabolites below to link to respective articles.[§ 1]

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|alt=Glycolysis and Gluconeogenesis edit]]

Glycolysis and Gluconeogenesis edit

1. The interactive pathway map can be edited at WikiPathways: "GlycolysisGluconeogenesis_WP534".