Sequential deletion of C-terminal amino acids of the E(1)alpha component of the pyruvate dehydrogenase (PDH) complex leads to reduced steady-state levels of functional E(1)alpha(2)beta(2) tetramers: implications for patients with PDH deficiency.
Hum Mol Genet 2000;
9:1041-8. [PMID:
10767328 DOI:
10.1093/hmg/9.7.1041]
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Abstract
Human pyruvate dehydrogenase (PDH) complex deficiency is an extremely heterogeneous disease in its presentation and clinical course. We have characterized novel mutations that affect the C-terminal portion of the PDH-E(1)alpha-coding sequence. Although the molecular defects underlying these mutations are different, both effectively produce a stop codon prematurely three amino acids from the C-terminus. The clinical and biochemical consequences of these mutations are unusual in that the affected individuals are very long-term survivors with PDH complex deficiency despite having low (<20%) activity in skin fibroblasts. These findings prompted us to investigate the C-terminus of E(1)alpha in greater detail. We constructed and expressed a series of PDH-E(1)alpha deletion mutants in a cell line with zero PDH complex activity due to a null E(1)alpha allele. Sequential deletion of the C-terminus by one, two, three and four amino acids resulted in PDH complex activities of 100, 60, 36 and 14%, respectively, compared with wild-type E(1)alpha expressed in PDH complex-deficient cells. The immunodetectable protein was decreased by the same amount as the activity, suggesting that the stability and/or assembly of the E(1)alpha(2)beta(2)heterotetramer might depend on the intactness of the PDH-E(1)alpha C-terminus. In addition, we compared the somatic and the testis-specific isoforms of E(1)alphaand concluded that they are biochemically equivalent.
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