title: Selenocysteine-containing thioredoxin reductase in C. elegans.
abstract: Mammalian thioredoxin reductases contain a TGA-encoded C-terminal penultimate selenocysteine (Sec) residue, and show little homology to bacterial, yeast, and plant thioredoxin reductases. Here we show that the nematode, Caenorhabditis elegans, contains two homologs related to the mammalian thioredoxin reductase family. The gene for one of these homologs contains a cysteine codon in place of TGA, and its product, designated TR-S, was previously suggested to function as thioredoxin reductase. The other gene contains TGA and its product is designated TR-Se. This Sec-containing thioredoxin reductase lacks a canonical Sec insertion sequence element in the 3'-untranslated area of the gene. TR-Se shows greater sequence similarity to mammalian thioredoxin reductase isozymes TR1 and TR2, whereas TR-S is more similar to TR3. TR-Se was identified as a thioredoxin reductase selenoprotein by labeling C. elegans with 75Se and characterizing the resulting 75Se-labeled protein by affinity and other column chromatography and gel-electrophoresis. TR-Se was expressed in Escherichia coli as a selenoprotein when a bacterial SECIS element was introduced downstream of the Sec TGA codon. The data show that TR-Se is the major naturally occurring selenoprotein in C. elegans, and suggest an important role for selenium and the thioredoxin system in this organism.
authors.affiliation: Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588, USA. vng@unlinfo2.unl.edu
authors.forename: V N
authors.initials: VN
authors.lastname: Gladyshev
authors.forename: M
authors.initials: M
authors.lastname: Krause
authors.forename: X M
authors.initials: XM
authors.lastname: Xu
authors.forename: K V
authors.initials: KV
authors.lastname: Korotkov
authors.forename: G V
authors.initials: GV
authors.lastname: Kryukov
authors.forename: Q A
authors.initials: QA
authors.lastname: Sun
authors.forename: B J
authors.initials: BJ
authors.lastname: Lee
authors.forename: J C
authors.initials: JC
authors.lastname: Wootton
authors.forename: D L
authors.initials: DL
authors.lastname: Hatfield
mesh_terms: D020413:3' Untranslated Regions; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000201:enzymology* / Q000235:genetics; D003001:Cloning, Molecular; D003062:Codon; D017124:Conserved Sequence; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D011506:Proteins / Q000737:chemistry / Q000235:genetics; D012644:Selenium Radioisotopes; D017279:Selenocysteine / Q000737:chemistry*; D051140:Selenoproteins; D016415:Sequence Alignment; D013880:Thioredoxin-Disulfide Reductase / Q000737:chemistry* / Q000235:genetics
chemical_list: D020413:3' Untranslated Regions; D003062:Codon; D015801:Helminth Proteins; D011506:Proteins; D012644:Selenium Radioisotopes; D051140:Selenoproteins; D017279:Selenocysteine; D013880:Thioredoxin-Disulfide Reductase