A novel regulatory mechanism based upon a dynamic core structure for the mitochondrial pyruvate dehydrogenase complex?

• The Arabidopsis genome encodes three forms of the mitochondrial PDC-E2 protein.
• Two E2 genes encode a monolipoyl enzyme, while the third encodes a dilipoyl form.
• Each E2 protein is able to form an icosahedral PDC core structure.
• One monolipoyl E2 protein has much higher in vitro activity than the other.
• We propose a regulatory mechanism with a dynamic core that exchanges E2 forms.

The Arabidopsis thaliana genome includes three genes for mitochondrial dihydrolipoamide acetyltransferase, the E2-component of the mitochondrial pyruvate dehydrogenase complex (PDC). Two genes encode E2-proteins with a single lipoyl domain, while the third has a two-lipoyl domain structure. Transcripts for each E2 protein were expressed in all plant organs. Each recombinant AtmtE2 can individually form an icosahedral PDC core structure, and results from bimolecular fluorescence complementation assays are consistent with formation of hetero-core structures from all permutations of the AtmtE2 proteins. We propose a unique regulatory mechanism involving dynamic formation of hetero-core complexes that include both mono- and di-lipoyl forms of AtmtE2.