title: A novel eukaryotic selenoprotein in the haptophyte alga Emiliania huxleyi.
abstract: The diversity of selenoproteins raises the question of why many life forms require selenium. Especially in photosynthetic organisms, the biochemical basis for the requirement for selenium is unclear because there is little information on selenoproteins. We found six selenium-containing proteins in a haptophyte alga, Emiliania huxleyi, which requires selenium for growth. The 27-kDa protein EhSEP2 was isolated, and its cDNA was cloned. The deduced amino acid sequence revealed that EhSEP2 is homologous to protein disulfide isomerase (PDI) and contains a highly conserved thioredoxin domain. The nucleotide sequence contains an in-frame TGA codon encoding selenocysteine at the position corresponding to the cysteine residue in the reaction center of known PDIs. However, no typical selenocysteine insertion sequence was found in the EhSEP2 cDNA. The EhSEP2 mRNA level was related to the abundance of selenium. E. huxleyi possesses a novel PDI-like selenoprotein and may have a novel type of selenocysteine insertion machinery.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Obata
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Shiraiwa
mesh_terms: D020418:Algal Proteins / Q000737:chemistry* / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D056890:Eukaryota / Q000737:chemistry / Q000201:enzymology / Q000235:genetics*; D005057:Eukaryotic Cells / Q000502:physiology*; D008969:Molecular Sequence Data; D019704:Protein Disulfide-Isomerases / Q000737:chemistry; D011506:Proteins / Q000737:chemistry* / Q000235:genetics*; D012643:Selenium / Q000502:physiology; D051140:Selenoproteins; D040681:Structural Homology, Protein
chemical_list: D020418:Algal Proteins; D011506:Proteins; D051140:Selenoproteins; D019704:Protein Disulfide-Isomerases; D012643:Selenium