Characterization of little skate (Leucoraja erinacea) recombinant transthyretin: Zinc-dependent 3,3′,5-triiodo-l-thyronine binding

Abstract

Transthyretin (TTR) diverged from an ancestral 5-hydroxyisourate hydrolase (HIUHase) by gene duplication at some early stage of chordate evolution. To clarify how TTR had participated in the thyroid system as an extracellular thyroid hormone (TH) binding protein, TH binding properties of recombinant little skate Leucoraja erinacea TTR was investigated. At the amino acid level, skate TTR showed 37-46% identities with the other vertebrate TTRs. Because the skate TTR had a unique histidine-rich segment in the N-terminal region, it could be purified by Ni-affinity chromatography. The skate TTR was a 46-kDa homotetramer of 14.5kDa subunits, and had one order of magnitude higher affinity for 3,3',5-triiodo-l-thyronine (T3) and some halogenated phenols than for l-thyroxine. However, the skate TTR had no HIUHase activity. Ethylenediaminetetraacetic acid (EDTA) treatment inhibited [(125)I]T3 binding activity whereas the addition of Zn(2+) to the EDTA-treated TTR recovered [(125)I]T3 binding activity in a Zn(2+) concentration-dependent manner. Scatchard analysis revealed the presence of two classes of binding site for T3, with dissociation constants of 0.24 and 17nM. However, the high-affinity sites were completely abolished with 1mM EDTA, whereas the remaining low-affinity sites decreased binding capacity. The number of zinc per TTR was quantified to be 4.5-6.3. Our results suggest that skate TTR has tight Zn(2+)-binding sites, which are essential for T3 binding to at least the high-affinity sites. Zn(2+) binding to the N-terminal histidine-rich segment may play an important role in acquisition or reinforcement of TH binding ability during early evolution of TTR.

Copper Isotopes and Copper to Zinc Ratio as Possible Biomarkers for Thyroid Cancer

“…Secondly, Zinc is a micronutrient required for the biosynthesis of thyroid hormones, and Zn affects the activity of 5′-deiodinase for the conversion of T4 to triiodothyronine (T3) ( 44 , 45 ). In addition, Zn is necessary for the synthesis of TSH from pituitary and TRH from hypothalamus ( 46 , 47 ). Kralik et al ( 48 ) showed Zn to be required for the correct metabolism of thyroid hormone, and Zn deficiency might have a negative effect on the activity of normal thyroid.…”

Changes in the Serum Levels of Trace Elements Before and After the Operation in Thyroid Cancer Patients

“…Zinc is an indispensable element in the functioning of 1,5′-deiodinase, which is necessary for the conversion of T 4 to T 3 [6]. Besides being required for the activity of thyroid hormones, zinc is essential for the synthesis of TSH from hypophysis and TRH from hypothalamus [7,21]. When the available information about the relation between zinc and thyroid is considered, changes in thyroid activity can be expected to result in variations in zinc levels.…”

Potential Disrupting Effects of Wastewater-Derived Disinfection Byproducts on Chinese Rare Minnow (Gobiocypris rarus) Transthyretin: An In Vitro and In Silico Study

“…In this study, the potential Chinese rare minnow (Gobiocypris rarus) transthyretin (CrmTTR) binding affinity of aromatic and aliphatic wastewater-derived DBPs was investigated by in vitro and in silico methods. The reasons why CrmTTR is selected are as follows: (a) transthyretin is one of the two thyroid hormone (TH) carrier proteins in fish, and previous studies had documented that the fish TTR could be disrupted by anthropogenic substances; − (b) our previous study documented that aromatic DBPs were high-affinity hTTR disruptors . As the endocrine disrupting effects of compounds may be likely species-dependent, it is not clear whether the aromatic wastewater-derived DBPs are also potential disruptors of fish transthyretin or not.…”