title: Biochemical and phylogenetic characterization of isocitrate dehydrogenase from a hyperthermophilic archaeon, Archaeoglobus fulgidus.
abstract: A thermostable homodimeric isocitrate dehydrogenase from the hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus was purified and characterized. The mol. mass of the isocitrate dehydrogenase subunit was 42 kDa as determined by SDS-PAGE. Following separation by SDS-PAGE, A. fulgidus isocitrate dehydrogenase could be renatured and detected in situ by activity staining. The enzyme showed dual coenzyme specificity with a high preference for NADP+. Optimal temperature for activity was 90 degrees C or above, and a half-life of 22 min was found for the enzyme when incubated at 90 degrees C in a 50 mM Tricine-KOH buffer (pH 8.0). Based on the N-terminal amino acid sequence, the gene encoding the isocitrate dehydrogenase was cloned. DNA sequencing identified the icd gene as an open reading frame encoding a protein of 412 amino acids with a molecular mass corresponding to that determined for the purified enzyme. The deduced amino acid sequence closely resembled that of the isocitrate dehydrogenase from the archaeon Caldococcus noboribetus (59% identity) and bacterial isocitrate dehydrogenases, with 57% identity with isocitrate dehydrogenase from Escherichia coli. All the amino acid residues directly contacting substrate and coenzyme (except Ile-320) in E. coli isocitrate dehydrogenase are conserved in the enzyme from A. fulgidus. The primary structure of A. fulgidus isocitrate dehydrogenase confirmes the presence of Bacteria-type isocitrate dehydrogenases among Archaea. Multiple alignment of all the available amino acid sequences of di- and multimeric isocitrate dehydrogenases from the three domains of life shows that they can be divided into three distinct phylogenetic groups.
authors.affiliation: Department of Microbiology, University of Bergen, Jahnebakken 5, N-5020 Bergen, Norway.
authors.forename: I H
authors.initials: IH
authors.lastname: Steen
authors.forename: T
authors.initials: T
authors.lastname: Lien
authors.forename: N K
authors.initials: NK
authors.lastname: Birkeland
mesh_terms: D000595:Amino Acid Sequence; D019611:Archaeoglobus fulgidus / Q000201:enzymology* / Q000235:genetics; D003001:Cloning, Molecular; D004795:Enzyme Stability; D019766:Genes, Archaeal / Q000235:genetics; D006358:Hot Temperature; D007521:Isocitrate Dehydrogenase / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D007526:Isoelectric Point; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D007521:Isocitrate Dehydrogenase