title: Cloning and characterization of type III iodothyronine deiodinase from the fish Oreochromis niloticus.
abstract: Type III iodothyronine deiodinase (D3) catalyzes the inner ring deiodination (IRD) of T4 and T3 to the inactive metabolites rT3 and 3,3'-diiodothyronine (3,3'-T2), respectively. Here we describe the cloning and characterization of complementary DNA (cDNA) coding for D3 in fish (Oreochromis niloticus, tilapia). This cDNA contains 1478 nucleotides and codes for a protein of 267 amino acids, including a putative selenocysteine (Sec) residue, encoded by a TGA triplet, at position 131. The deduced amino acid sequence shows 57-67% identity with frog, chicken, and mammalian D3, 33-39% identity with frog, fish (Fundulus heteroclitus) and mammalian D2, and 30-35% identity with fish (tilapia), chicken, and mammalian D1. The 3' UTR contains a putative Sec insertion sequence (SECIS) element. Recombinant tilapia D3 (tD3) expressed in COS-1 cells and native tD3 in tilapia brain microsomes show identical catalytic activities, with a strong preference for IRD of T3 (Km approximately 20 nM). IRD of [3,5-125I]T3 by native and recombinant tD3 are equally sensitive to inhibition by substrate analogs (T3 > T4 >> rT3) and inhibitors (gold thioglucose >> iodoacetate > propylthiouracil). Northern analysis using a tD3 riboprobe shows high expression of a 1.6-kb messenger RNA in gill and brain, although D3 activity is much higher in brain than in gill. The characterization of tD3 cDNA provides new information about the structure-activity relationship of iodothyronine deiodinases and an important tool to study the regulation of thyroid hormone bioactivity in fish.
authors.affiliation: Department of Internal Medicine III, Erasmus University Medical School, Rotterdam, The Netherlands.
authors.forename: J P
authors.initials: JP
authors.lastname: Sanders
authors.forename: S
authors.initials: S
authors.lastname: Van der Geyten
authors.forename: E
authors.initials: E
authors.lastname: Kaptein
authors.forename: V M
authors.initials: VM
authors.lastname: Darras
authors.forename: E R
authors.initials: ER
authors.lastname: Kühn
authors.forename: J L
authors.initials: JL
authors.lastname: Leonard
authors.forename: T J
authors.initials: TJ
authors.lastname: Visser
mesh_terms: D020413:3' Untranslated Regions / Q000737:chemistry / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002645:Chickens; D003001:Cloning, Molecular; D018076:DNA, Complementary; D006801:Humans; D007453:Iodide Peroxidase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009928:Organ Specificity; D011892:Rana catesbeiana; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D017210:Tilapia / Q000235:genetics*; D014982:Xenopus laevis
chemical_list: D020413:3' Untranslated Regions; D018076:DNA, Complementary; D011994:Recombinant Proteins; C117274:iodothyronine deiodinase type III; D007453:Iodide Peroxidase