title: Cloning and characterization of a type 3 iodothyronine deiodinase (D3) in the liver of the chondrichtyan Chiloscyllium punctatum.
abstract: Thyroid hormone bioactivity is finely regulated at the cellular level by the peripheral iodothyronine deiodinases (D). The study of thyroid function in fish has been restricted mainly to teleosts, whereas the study and characterization of Ds have been overlooked in chondrichthyes. Here we report the cloning and operational characterization of both the native and the recombinant hepatic type 3 iodothyronine deiodinase in the tropical shark Chiloscyllium punctatum. Native and recombinant sD3 show identical catalytic activities: a strong preference for T3-inner-ring deiodination, a requirement for a high concentration of DTT, a sequential reaction mechanism, and resistance to PTU inhibition. The cloned cDNA contains 1298 nucleotides [excluding the poly(A) tail] and encodes a predicted protein of 259 amino acids. The triplet TGA coding for selenocysteine (Sec) is at position 123. The consensus selenocysteine insertion sequence (SECIS) was identified 228 bp upstream of the poly(A) tail and corresponds to form 2. The deduced amino acid sequence was 77% and 72% identical to other D3 cDNAs in fishes and other vertebrates, respectively. As in the case of other piscivore teleost species, shark expresses hepatic D3 through adulthood. This characteristic may be associated with the alimentary strategy in which the protection from an exogenous overload of thyroid hormones could be of physiological importance for thyroidal homeostasis.
authors.affiliation: Instituto de Neurobiología, Departamento de Neurobiología Celular y Molecular, Universidad Nacional Autónoma de, Campus UNAM-UAQ, Juriquilla, ORO 76230 Querétaro, Mexico. lidiamm2@yahoo.com.mx <lidiamm2@yahoo.com.mx>
authors.forename: Lidia Mayorga
authors.initials: LM
authors.lastname: Martínez
authors.forename: Aurea
authors.initials: A
authors.lastname: Orozco
authors.forename: Patricia
authors.initials: P
authors.lastname: Villalobos
authors.forename: Carlos
authors.initials: C
authors.lastname: Valverde-R
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D007453:Iodide Peroxidase / Q000235:genetics*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D012754:Sharks / Q000378:metabolism*; D013963:Thyroid Hormones / Q000378:metabolism / Q000502:physiology
chemical_list: D018076:DNA, Complementary; D011994:Recombinant Proteins; D013963:Thyroid Hormones; D007453:Iodide Peroxidase