Mammalian selenoproteins.
Selenium (Se) is an essential trace element for animals and humans. Its biological role was established following the discovery that Se is a structural component of the active center of the enzyme glutathione peroxidase (GSH-Px). During the last decade remarkable progress has been made in the recognition of the structure and function of several selenoproteins. Cellular GSH-Px was the first enzyme recognized as a selenoprotein. In it Se was found in the form of selenocysteine. The enzyme is a tetrameric protein and is composed of four apparently identical subunits each containing one gram atom of Se. Plasma GSH-Px also has a tetrameric form with identical subunits and with one atom of Se per subunit. It is, however, a glycosylated protein, and is distinct from cellular enzyme. Both enzymes catalyze the reduction of hydrogen peroxide and a variety of organic hydroperoxides by glutathione. A third GSH-Px, called phospholipid hydroperoxide glutathione peroxidase (PHGSH-Px), is a monomeric, membrane-associated enzyme containing one atom of Se per mole of protein. This enzyme destroys esterified lipid hydroperoxides. The fourth known mammalian selenoenzyme is a type I iodothyronine 5'-deiodinase that catalyzes the deiodination of L-thyroxine to the biologically active hormone 3,3',5-triiodothyronine. It is a monomeric enzyme and contains one atom of Se per mole of protein. Selenoprotein P, a fifth known selenoprotein, is a glycosylated, monomeric protein containing ten atoms of Se per molecule. The function of this protein is not known, but it may play a role in Se transport or be connected with a protective activity against free radicals. In all these selenoproteins the Se is incorporated into the protein molecule via the selenocysteinyl-tRNA which recognizes the specific UGA codons in mRNAs to insert selenocysteine into the primary structure of selenoproteins.
Zachara
B A
BA
Department of Biochemistry, Medical School, Bydgoszcz, Poland.
D000595:Amino Acid Sequence; D000818:Animals; D005609:Free Radicals; D005979:Glutathione Peroxidase / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007453:Iodide Peroxidase / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D011506:Proteins / Q000737:chemistry / Q000502:physiology*; D012333:RNA, Messenger; D012643:Selenium / Q000378:metabolism*; D051149:Selenoprotein P; D051140:Selenoproteins; D016415:Sequence Alignment; D014961:X-Ray Diffraction
D005609:Free Radicals; D011506:Proteins; D012333:RNA, Messenger; D051149:Selenoprotein P; D051140:Selenoproteins; D007453:Iodide Peroxidase; D005979:Glutathione Peroxidase; D012643:Selenium