Asp295 stabilizes the active-site loop structure of pyruvate dehydrogenase, facilitating phosphorylation of ser292 by pyruvate dehydrogenase-kinase

A mutation in the E2 subunit of the mitochondrial pyruvate dehydrogenase complex in Arabidopsis reduces plant organ size and enhances the accumulation of amino acids and intermediate products of the TCA cycle

The mitochondrial pyruvate dehydrogenase complex (mtPDC) plays a pivotal role in controlling the entry of carbon into the tricarboxylic acid (TCA) cycle for energy production. This multi-enzyme complex consists of three components: E1, E2, and E3. In Arabidopsis, there are three genes, mtE2-1, mtE2-2, and mtE2-3, which encode the putative mtPDC E2 subunit but how each of them contributes to the total mtPDC activity remains unknown. In this work, we characterized an Arabidopsis mutant, m132, that has abnormal small organs. Molecular cloning indicated that the phenotype of m132 is caused by a mutation in the mtE2-1 gene, which results in a truncation of 109 amino acids at the C-terminus of the encoded protein. In m132, mtPDC activity is only 30% of the WT and ATP production is severely impaired. The mutation in the mtE2-1 gene also leads to the over-accumulation of most intermediate products of the TCA cycle and of all the amino acids for protein synthesis. Our results suggest that, among the three mtE2 genes, mtE2-1 is a major contributor to the function of Arabidopsis mtPDC and that the functional disruption of mtE2-1 profoundly affects plant growth and development, as well as its metabolism.

"Scanning mutagenesis" of the amino acid sequences flanking phosphorylation site 1 of the mitochondrial pyruvate dehydrogenase complex

The mitochondrial pyruvate dehydrogenase complex (mtPDC) is regulated by reversible seryl-phosphorylation of the E1α subunit by a dedicated, intrinsic kinase. The phospho-complex is reactivated when dephosphorylated by an intrinsic PP2C-type protein phosphatase. Both the position of the phosphorylated Ser-residue and the sequences of the flanking amino acids are highly conserved. We have used the synthetic peptide-based kinase client (KiC) assay plus recombinant pyruvate dehydrogenase E1α and E1α-kinase to perform "scanning mutagenesis" of the residues flanking the site of phosphorylation. Consistent with the results from "phylogenetic analysis" of the flanking sequences, the direct peptide-based kinase assays tolerated very few changes. Even conservative changes such as Leu, Ile, or Val for Met, or Glu for Asp, gave very marked reductions in phosphorylation. Overall the results indicate that regulation of the mtPDC by reversible phosphorylation is an extreme example of multiple, interdependent instances of co-evolution.