title: 2-Oxoacid dehydrogenase multienzyme complexes in the halophilic Archaea? Gene sequences and protein structural predictions.
abstract: All Archaea catalyse the conversion of pyruvate to acetyl-CoA via a simple pyruvate oxidoreductase. This is in contrast to the Eukarya and most aerobic bacteria, which use the pyruvate dehydrogenase multienzyme complex [PDHC], consisting of multiple copies of three component enzymes: E1 (pyruvate decarboxylase), E2 (lipoate acetyl-transferase) and E3 (dihydrolipoamide dehydrogenase, DHLipDH). Until now no PDHC activity has been found in the Archaea, although DHLipDH has been discovered in the extremely halophilic Archaea and its gene sequence has been determined. In this paper, the discovery and sequencing of an operon containing the DHLipDH gene in the halophilic archaeon Haloferax volcanii are reported. Upstream of the DHLipDH gene are 3 ORFs which show highest sequence identities with the E1alpha, E1beta and E2 genes of the PDHC from gram-positive organisms. Structural predictions of the proposed protein product of the E2 gene show a domain structure characteristic of the E2 component in PDHCs, and catalytically important residues, including the lysine to which the lipoic acid cofactor is covalently bound, are conserved. Northern analyses indicate the transcription of the whole operon, but no PDHC enzymic activity could be detected in cell extracts. The presence in the E2 gene of an insertion (equivalent to approximately 100 aa) not found in bacterial or eukaryal E2 proteins, might be predicted to prevent multienzyme complex assembly. This is the first detailed report of the genes for a putative 2-oxoacid dehydrogenase complex in the Archaea, and the evolutionary and metabolic consequences of these findings are discussed.
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK1.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Jolley
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK1.
authors.forename: Deborah G
authors.initials: DG
authors.lastname: Maddocks
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK1.
authors.forename: Shan L
authors.initials: SL
authors.lastname: Gyles
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK1.
authors.forename: Zoë
authors.initials: Z
authors.lastname: Mullan
authors.affiliation: Department of Microbiology & Immunology, University of Melbourne, Parkville, Australia2.
authors.forename: Sen-Lin
authors.initials: SL
authors.lastname: Tang
authors.affiliation: Department of Microbiology & Immunology, University of Melbourne, Parkville, Australia2.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Dyall-Smith
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK1.
authors.forename: David W
authors.initials: DW
authors.lastname: Hough
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK1.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Danson
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics*; D001483:Base Sequence; D019766:Genes, Archaeal; D016931:Halobacteriales / Q000201:enzymology / Q000235:genetics*; D007658:Ketone Oxidoreductases / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics*; D016366:Open Reading Frames; D009876:Operon; D015221:Potassium Channels / Q000235:genetics; D016415:Sequence Alignment; D051637:Shaker Superfamily of Potassium Channels
chemical_list: D019843:Archaeal Proteins; D009097:Multienzyme Complexes; D015221:Potassium Channels; D051637:Shaker Superfamily of Potassium Channels; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)