title: Characteristics of the brown hagfish Paramyxine atami transthyretin: Metal ion-dependent thyroid hormone binding.
abstract: Transthyretin (TTR) is a vertebrate-specific protein involved in thyroid hormone distribution in plasma, and its gene is thought to have emerged by gene duplication from the gene for the ancient TTR-related protein, 5-hydroxyisourate hydrolase, at some early stage of chordate evolution. We investigated the molecular and hormone-binding properties of the brown hagfish Paramyxine atami TTR. The amino acid sequence deduced from the cloned hagfish TTR cDNA shared 33-50% identities with those of other vertebrate TTRs but less than 24% identities with those of vertebrate and deuterostome invertebrate 5-hydroxyisourate hydrolases. Hagfish TTR, as well as lamprey and little skate TTRs, had an N-terminal histidine-rich segment, allowing purification by metal-affinity chromatography. The affinity of hagfish TTR for 3,3',5-triiodo-L-thyronine (T3) was 190 times higher than that for L-thyroxine, with a dissociation constant of 1.5-3.9nM at 4°C. The high-affinity binding sites were strongly sensitive to metal ions. Zn2+and Cu2+decreased the dissociation constant to one-order of magnitude, whereas a chelator, o-phenanthroline, increased it four times. The number of metal ions (mainly Zn2+and Cu2+) was approximately 12/TTR (mol/mol). TTR was also a major T3-binding protein in adult hagfish sera and its serum concentration was approximately 8μM. These results suggest that metal ions and the acquisition of N-terminal histidine-rich segment may cooperatively contribute to the evolution toward an ancient TTR with high T3 binding activity from either 5-hydroxyisourate hydrolase after gene duplication.
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Shizuoka 422-8529, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Shizuoka 422-8529, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Kasai
authors.affiliation: Department of Biology, School of Medicine, Fukushima Medical University, Fukushima 960-1295, Japan.
authors.forename: Norihito
authors.initials: N
authors.lastname: Nishiyama
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Shizuoka 422-8529, Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Ishihara
authors.affiliation: Department of Biological Science, Graduate School of Science, Shizuoka University, Shizuoka 422-8529, Japan. Electronic address: yamauchi.kiyoshi@shizuoka.ac.jp.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Yamauchi
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002413:Cations, Divalent / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D020869:Gene Expression Profiling; D006196:Hagfishes / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008670:Metals / Q000494:pharmacology*; D010802:Phylogeny; D011228:Prealbumin / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D044967:Serum / Q000378:metabolism; D013963:Thyroid Hormones / Q000378:metabolism*; D013997:Time Factors; D014284:Triiodothyronine / Q000378:metabolism; D014527:Uric Acid / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: C510200:5-hydroxyisourate; D002413:Cations, Divalent; D018076:DNA, Complementary; D008670:Metals; D011228:Prealbumin; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013963:Thyroid Hormones; D014284:Triiodothyronine; D014527:Uric Acid; D000581:Amidohydrolases; C474249:hydroxyisourate hydrolase
keywords: Evolution; Metal ions; Paramyxine atami; Thyroid hormone; Transthyretin