Primary structure of an invertebrate dihydrolipoamide dehydrogenase with phylogenetic relationship to vertebrate and bacterial disulfide oxidoreductases

Dihydrolipoamide dehydrogenase (E₃) is a flavoprotein component of multi-enzyme complexes catalyzing oxidative decarboxylation of -ketoacids in the Krebs' cycle. We have cloned a 2.4-kb E₃ cDNA from an arthropod, Manduca sexta, that codes for 497 amino acids and translates to a 51-kDa protein in vitro. Sequences at and around the dinucleotide binding domains, disulfide active site and the C-terminal interface domain involved in substrate binding are highly conserved in Manduca E₃. Phylogenetic analysis of protein sequences from the flavoprotein class of disulfide oxidoreductases family of enzymes suggests that in spite of the homologous nature of E₃ and glutathione reductase (goR) in sequence and structure, E₃ shares a common ancestor with mercuric reductase (merA), whereas goR is more related to trypanothione reductase (tryR) than to other members. All members, except goRs, seemed to be monophyletic. Plant goRs seemed to have arisen differently and are more closely related to tryRs than to bacterial and vertebrate goRs. Earlier speculation on the nature of origin of E₃ in Pseudomonas is not supported by phylogenetic data. A possible structural relationship of Manduca E₃ to other pyridine-binding proteins, such as the neurotransmitter transporters and channels, is proposed.