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Change in structure of the N‐terminal region of transthyretin produces change in affinity of transthyretin to T4 and T3
Author(s) -
Prapunpoj Porntip,
Leelawatwatana Ladda,
Schreiber Gerhard,
Richardson Samantha J.
Publication year - 2006
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2006.05404.x
Subject(s) - transthyretin , tetramer , recombinant dna , chemistry , dissociation constant , pichia pastoris , triiodothyronine , biochemistry , endocrinology , hormone , biology , enzyme , gene , receptor
The relationship between the structure of the N‐terminal sequence of transthyretin (TTR) and the binding of thyroid hormone was studied. A recombinant human TTR and two derivatives of Crocodylus porosus TTRs, one with the N‐terminal sequence replaced by that of human TTR (human/crocTTR), the other with the N‐terminal segment removed (truncated crocTTR), were synthesized in Pichia pastoris . Subunit mass, native molecular weight, tetramer formation, cross‐reactivity to TTR antibodies and binding to retinol‐binding protein of these recombinant TTRs were similar to TTRs found in nature. Analysis of the binding affinity to thyroid hormones of recombinant human TTR showed a dissociation constant ( K d ) for triiodothyronine (T3) of 53.26 ± 3.97 n m and for thyroxine (T4) of 19.73 ± 0.13 n m . These values are similar to those found for TTR purified from human serum, and gave a K d T3/T4 ratio of 2.70. The affinity for T4 of human/crocTTR ( K d = 22.75 ± 1.89 n m ) was higher than those of both human TTR and C. porosus TTR, but the affinity for T3 ( K d = 5.40 ± 0.25 n m ) was similar to C. porosus TTR, giving a K d T3/T4 ratio of 0.24. A similar affinity for both T3 ( K d = 57.78 ± 5.65 n m ) and T4 ( K d = 59.72 ± 3.38 n m ), with a K d T3/T4 ratio of 0.97, was observed for truncated crocTTR. The obtained results strongly confirm the hypothesis that the unstructured N‐terminal region of TTR critically influences the specificity and affinity of thyroid hormone binding to TTR.