title: Euglena gracilis ribonucleotide reductase: the eukaryote class II enzyme and the possible antiquity of eukaryote B12 dependence.
abstract: Ribonucleotide reductases provide the building blocks for DNA synthesis. Three classes of enzymes are known, differing widely in amino acid sequence but with similar structural motives and allosteric regulation. Class I occurs in eukaryotes and aerobic prokaryotes, class II occurs in aerobic and anaerobic prokaryotes, and class III occurs in anaerobic prokaryotes. The eukaryote Euglena gracilis contains a class II enzyme (Gleason, F. K., and Hogenkamp, H. P. (1970) J. Biol. Chem. 245, 4894-4899) and, thus, forms an exception. Class II enzymes depend on vitamin B(12) for their activity. We purified the reductase from Euglena cells, determined partial peptide sequences, identified its cDNA, and purified the recombinant enzyme. Its amino acid sequence and general properties, including its allosteric behavior, were similar to the class II reductase from Lactobacillus leichmannii. Both enzymes belong to a distinct small group of reductases that unlike all other homodimeric reductases are monomeric. They compensate the loss of the second polypeptide of dimeric enzymes by a large insertion in the monomeric chain. Data base searching and sequence comparison revealed a homolog from the eukaryote Dictyostelium discoideum as the closest relative to the Euglena reductase, suggesting that the class II enzyme was present in a common, B(12)-dependent, eukaryote ancestor.
authors.affiliation: Department of Molecular Biology and Functional Genomics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691 Stockholm, Sweden.
authors.forename: Eduard
authors.initials: E
authors.lastname: Torrents
authors.forename: Chiara
authors.initials: C
authors.lastname: Trevisiol
authors.forename: Carmen
authors.initials: C
authors.lastname: Rotte
authors.forename: Ulf
authors.initials: U
authors.lastname: Hellman
authors.forename: William
authors.initials: W
authors.lastname: Martin
authors.forename: Peter
authors.initials: P
authors.lastname: Reichard
mesh_terms: D020418:Algal Proteins / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D005056:Euglena gracilis / Q000201:enzymology*; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D015800:Protozoan Proteins / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016415:Sequence Alignment; D014805:Vitamin B 12 / Q000378:metabolism*
chemical_list: D020418:Algal Proteins; D001426:Bacterial Proteins; D015800:Protozoan Proteins; D011994:Recombinant Proteins; D012264:Ribonucleotide Reductases; D014805:Vitamin B 12