Browsing by Author "Lundberg, Erik"
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- High resolution crystal structures of piscine transthyretin reveal different binding modes for triiodothyronine and thyroxinePublication . Eneqvist, Therese; Lundberg, Erik; Karlsson, Anders; Huang, Shenghua; Santos, Cecilia; Power, Deborah; Sauer-Eriksson, A. ElisabethTransthyretin (TTR) is an extracellular transport protein involved in the distribution of thyroid hormones and vitamin A. So far, TTR has only been found in vertebrates, of which piscine TTR displays the lowest sequence identity with human TTR (47%). Human and piscine TTR bind both thyroid hormones 3,5,3 -triiodo- L-thyronine (T3) and 3,5,3 ,5 -tetraiodo-L-thyronine (thyroxine, T4). Human TTR has higher affinity for T4 than T3, whereas the reverse holds for piscine TTR. X-ray structures of Sparus aurata (sea bream) TTR have been determined as the apo-protein at 1.75 Å resolution and bound to ligands T3 and T4, both at 1.9 Å resolution. The apo structure is similar to human TTR with structural changes only at -strand D. This strand forms an extended loop conformation similar to the one in chicken TTR. The piscine TTR T4 complex shows the T4-binding site to be similar but not identical to human TTR, whereas the TTR T3 complex shows the I3 halogen situated at the site normally occupied by the hydroxyl group of T4. The significantly wider entrance of the hormone- binding channel in sea bream TTR, in combination with its narrower cavity, provides a structural explanation for the different binding affinities of human and piscine TTR to T3 and T4.
- Hormone affinity and fibril formation of piscine transthyretin: the role of the N-terminalPublication . Morgado, Isabel; Melo, Eduardo P.; Lundberg, Erik; Estrela, Nídia L.; Sauer-Eriksson, A. Elisabeth; Power, DeborahTransthyretin (TTR) transports thyroid hormones (THs), thyroxine (T4) and triiodothyronine (T3) in the blood of vertebrates. TH-binding sites are highly conserved in vertebrate TTR however, piscine TTR has a longer N-terminus which is thought to influence TH-binding affinity and may influence TTR stability. We produced recombinant wild-type sea bream TTR (sbTTRWT) plus two mutants in which six (sbTTRM6) and twelve (sbTTRM12) N-terminal residues were removed. Ligandbinding studies revealed similar affinities for T3 (Kd=10.6±1.7nM) and T4 (Kd=9.8±0.97nM) binding to sbTTRWT. Affinity for THs was unaltered in sbTTRM12 but sbTTRM6 had poorer affinity for T4 (Kd=252.3±15.8nM) implying that some residues in the N-terminus can influence T4 binding. sbTTRM6 inhibited acid-mediated fibril formation in vitro as shown by fluorometric measurements using thioflavine-T.In contrast, fibril formation by sbTTRM12 was significant, probably due to decreased stability of the tetramer. Such studies also suggested that sbTTRWT is more resistant to fibril formation than human TTR.