Glycan-Dependent Mutual and Reversible Sequestration of Two XXXX .

@entity1669 @entity1112 @entity3745 @entity14813 @entity259
BACKGROUND: @entity3745 (Tg), the major thyroidal protein, plays important roles in thyroid hormone biosynthesis and in @entity1669 ( @entity1669 ). Tg also serves as a pre- and postoperative biomarker of @entity259 ( @entity259 ). The endogenous b-galactoside binding lectin @entity14813 ( @entity14813 ), secreted by transformed thyroid cells, has been shown to be another useful biomarker of @entity259 . Tg contains @entity1112 that can serve as binding epitopes of @entity14813 . The objective of the study is to investigate the interaction between Tg and @entity14813 and discuss its potential consequences. METHODS: Binding interaction between Tg and @entity14813 was first studied by hemagglutination inhibition assays. Subsequently, a detailed analysis of binding thermodynamics was carried out by isothermal titration calorimetry. Quantitative precipitation was performed to study the complex formation between Tg and @entity14813 and to determine the binding stoichiometry. The concentration-dependent rate and amount of complex formation between Tg and @entity14813 was examined spectrophotometrically. A similar approach was taken to study the effect of free Tg and @entity14813 on preformed Tg- @entity14813 complex. RESULTS: Quantitative biochemical and biophysical data show that these two biomarkers produced by @entity259 cells interact with each other with submicromolar affinity and form an insoluble complex at their stoichiometric concentration. One Tg molecule could bind up to 14 molecules of @entity14813 . Such complex formation mutually sequestered both Tg and @entity14813 , decreasing the concentration of their freely available forms. Formation of the Tg- @entity14813 complex was reversible as the preformed complex was dissolved by free Tg as well as free @entity14813 . While free Tg rapidly dissolved preformed Tg- @entity14813 complex in a concentration-dependent manner, @entity14813 was found to be much less efficient and slowly dissolved only a fraction of the preformed complex at a relatively higher @entity14813 concentration. CONCLUSIONS: Complex formation between Tg and @entity14813 through high affinity binding and the sensitivity of the complex to free Tg and @entity14813 can potentially influence their biological functions. Interactions between Tg and @entity14813 might also interfere with their clinical detection, the same way Tg autoantibody (TgAb) is reported to interfere with Tg assays. The data support a model of @entity14813 -mediated homeostatic process of Tg.
