Cloning and sequencing of cDNAs encoding alpha and beta subunits of human pyruvate dehydrogenase

Abstract

The cDNAs encoding fragments of the alpha and beta subunits (PDH alpha and PDH beta) of human pyruvate dehydrogenase (PDH, EC 1.2.4.1) were isolated from a HeLa cell cDNA library in the lambda gt11 expression vector by immunoscreening. Phage cDNA fragments were subsequently used to screen a human foreskin fibroblast cDNA library by colony hybridization. Nucleotide sequence analyses of the positive plasmid clones (pHPDA and pHPDB) revealed an insert of 1.36 kilobases (kb) for PDH alpha and one of 1.69 kb for PDH beta, respectively, allowing us to predict the complete amino acid sequences of the precursor and mature proteins of these two subunits. A putative leader sequence of 29 amino acid residues was identified in pHPDA, resulting in a precursor protein of 392 amino acid residues (Mr 43,414) and a mature protein of 363 residues (Mr 40,334). A similar leader sequence of 30 amino acid residues in pHPDB was also identified, resulting in a precursor protein of 359 amino acid residues (Mr 39,046) and a mature protein of 329 residues (Mr 35,911). The amino acid sequences of NH2-terminal regions of the two subunits of human PDH were highly homologous with those of mature porcine PDH. The amino acid sequences of phosphorylation sites determined in PDH alpha of bovine and porcine enzymes were also conserved in the human PDH alpha. Blot analysis of HeLa cell poly(A)+ RNA showed a single mRNA of 1.8 kb for PDH alpha and 1.7 kb for PDH beta, respectively. The precursor proteins of PDH alpha and PDH beta were detected by immunoprecipitation from an 35S-labeled cell-free translation system.