PRIMARY STRUCTURE OF AN INVERTEBRATE DIHYDROLIPOAMIDE DEHYDROGENASE WITH PHYLOGENETIC RELATIONSHIP TO VERTEBRATE AND BACTERIAL DISULFIDE OXIDOREDUCTASES

Dihydrolipoamide dehydrogenase (E-3) is a flavoprotein component of mu lti-enzyme complexes catalyzing oxidative decarboxylation of alpha-ket oacids in the Krebs' cycle. We have cloned a 2.4-kb E-3 cDNA from an a rthropod, Manduca sexta, that codes for 497 amino acids and translates to a 51-kDa protein in vitro. Sequences at and around the dinucleotid e binding domains, disulfide active site and the C-terminal interface domain involved in substrate binding are highly conserved in Manduca E -3. Phylogenetic analysis of protein sequences from the flavoprotein c lass of disulfide oxidoreductases family of enzymes suggests that in s pite of the homologous nature of E-3 and glutathione reductase (goR) i n sequence and structure, E-3 shares a common ancestor with mercuric r eductase (merA), whereas goR is more related to trypanothione reductas e (tryR) than to other members. All members, except goRs, seemed to be monophyletic. Plant goRs seemed to have arisen differently and are mo re closely related to tryRs than to bacterial and vertebrate goRs. Ear lier speculation on the nature of origin of E-3 in Pseudomonas is not supported by phylogenetic data. A possible structural relationship of Manduca E-3 to other pyridine-binding proteins, such as the neurotrans mitter transporters and channels, is proposed. (C) 1997 Elsevier Scien ce B.V.