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Transthyretin and the transthyretin-related protein: A structural study
Umeå University, Faculty of Science and Technology, Umeå Centre for Molecular Pathogenesis (UCMP) (Faculty of Science and Technology).
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Transthyretin (TTR) is one of several proteins involved in amyloid disease in humans. Unknown conformational changes of the native state of TTR result in aggregation of TTR molecules into amyloid fibrils, which accumulate in extracellular tissues. This may result in different clinical symptoms, e.g. polyneuropathy or cardiomyopathy, depending on their site of accumulation.

Our long-term goal is to identify structural changes associated with amyloid formation. For this work, structural characterization of TTR from other species than human may provide valuable information.

The three-dimensional X-ray crystallographic structure of TTR from sea bream (Sparus aurata) was determined at 1.75 Å resolution. Human and sea bream TTR were found to be structurally very similar. However, interesting differences were present in the area at and around -strand D, which in fish forms an extended loop region. Interestingly, this area is believed to dissociate from the structure prior to amyloid formation, to allow -strands A and B to participate in polymerization.

During evolution, TTR from different species have developed differences in preference to their natural ligands, the thyroid hormones 3,5,3’-triiodo-L-thyronine (T3) and 3,5,3’,5’-tetraiodo-L-thyronine (T4). While human TTR has higher affinity for T4, the opposite is true in lower vertebrates, e.g. fish and reptiles. We have determined two separate structures of sea bream TTR in complex with T3 and T4, both at 1.9 Å resolution. A significantly wider entrance and narrower thyroid hormone binding channel provide a structural explanation to the differences in thyroid hormone preference between human and piscine TTR.

In a separate work, we identified a novel protein family with structural similarity to TTR, which we named the transthyretin-related protein (TRP) family. To attain information about this protein family, we cloned, expressed, purified and characterized TRP from Escherichia coli (EcTRP). Furthermore, we solved the structure of EcTRP to 1.65 Å resolution. As predicted, EcTRP and human TTR are structurally very similar. Interesting structural differences are found in the area corresponding to the thyroid hormone binding site in TTR, which due to its amino acid conservation within the TRP family we identified as a putative ligand-binding site in TRPs. The function of the TRP is not known, however, recent studies suggest that it might be involved in purine catabolism.

It has been shown that partial acid denaturation of human TTR results in amyloid-fibril formation. Interestingly, we have shown that sea bream TTR also forms amyloid-like fibrils in vitro, even though it shares only 52% sequence identity to human TTR. Corresponding studies on EcTRP did not generate amyloid-like fibrils. EcTRP has 30% sequence identity to human TTR. The fact that two of the proteins form amyloid fibrils and one does not means that they can serve as a model system for the study of amyloid formation. Further studies on these three proteins are currently performed to attain more information about the mechanism of amyloid formation.

Place, publisher, year, edition, pages
Umeå: Umeå centrum för molekylär patogenes (UCMP) (Teknisk-naturvetenskaplig fakultet) , 2006. , 44 p.
Keyword [en]
Transthyretin, Transthyretin-related protein, X-ray crystallography, Protein structure, Amyloidosis
National Category
Structural Biology
Identifiers
URN: urn:nbn:se:umu:diva-744ISBN: 91-7264-064-2 (print)OAI: oai:DiVA.org:umu-744DiVA: diva2:144400
Public defence
2006-04-28, Astrid Fagreus-salen, 6A103, 6A, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2006-04-06 Created: 2006-04-06 Last updated: 2011-03-15Bibliographically approved
List of papers
1. High resolution crystal structures of piscine transthyretin reveal different binding modes for triiodothyronine and thyroxine.
Open this publication in new window or tab >>High resolution crystal structures of piscine transthyretin reveal different binding modes for triiodothyronine and thyroxine.
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2004 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, Vol. 279, no 25, 26411-6 p.Article in journal (Refereed) Published
Abstract [en]

Transthyretin (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 (T(3)) and 3,5,3',5'-tetraiodo-l-thyronine (thyroxine, T(4)). Human TTR has higher affinity for T(4) than T(3), 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 A resolution and bound to ligands T(3) and T(4), both at 1.9 A resolution. The apo structure is similar to human TTR with structural changes only at beta-strand D. This strand forms an extended loop conformation similar to the one in chicken TTR. The piscine TTR.T(4) complex shows the T(4)-binding site to be similar but not identical to human TTR, whereas the TTR.T(3) complex shows the I3' halogen situated at the site normally occupied by the hydroxyl group of T(4). 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 T(3) and T(4).

Keyword
Animals, Chickens, Cloning; Molecular, Crystallography; X-Ray, Escherichia coli/metabolism, Humans, Ligands, Models; Molecular, Prealbumin/*chemistry/metabolism, Protein Binding, Protein Conformation, Protein Structure; Tertiary, Sea Bream, Thyroxine/*chemistry, Triiodothyronine/*chemistry
Identifiers
urn:nbn:se:umu:diva-13622 (URN)10.1074/jbc.M313553200 (DOI)15082720 (PubMedID)
Available from: 2007-10-12 Created: 2007-10-12Bibliographically approved
2. The transthyretin-related protein family
Open this publication in new window or tab >>The transthyretin-related protein family
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2003 (English)In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 270, no 3, 518-532 p.Article in journal (Refereed) Published
Abstract [en]

A number of proteins related to the homotetrameric transport protein transthyretin (TTR) forms a highly conserved protein family, which we present in an integrated analysis of data from different sources combined with an initial biochemical characterization. Homologues of the transthyretin-related protein (TRP) can be found in a wide range of species including bacteria, plants and animals, whereas transthyretins have so far only been identified in vertebrates. A multiple sequence alignment of 49 TRP sequences from 47 species to TTR suggests that the tertiary and quaternary features of the three-dimensional structure are most likely preserved. Interestingly, while some of the TRP orthologues show as little as 30% identity, the residues at the putative ligand-binding site are almost entirely conserved. RT/PCR analysis in Caenorhabditis elegans confirms that one TRP gene is transcribed, spliced and predominantly expressed in the worm, which suggests that at least one of the two C. elegans TRP genes encodes a functional protein. We used double-stranded RNA-mediated interference techniques in order to determine the loss-of-function phenotype for the two TRP genes in C. elegans but detected no apparent phenotype. The cloning and initial characterization of purified TRP from Escherichia coli reveals that, while still forming a homotetramer, this protein does not recognize thyroid hormones that are the natural ligands of TTR. The ligand for TRP is not known; however, genomic data support a functional role involving purine catabolism especially linked to urate oxidase (uricase) activity.

Place, publisher, year, edition, pages
John Wiley & Sons, 2003
Keyword
Escherichia coli, homology model, purine catabolism, sequence analysis, transthyretin-related protein
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-5045 (URN)10.1046/j.1432-1033.2003.03408.x (DOI)
Available from: 2006-04-06 Created: 2006-04-06 Last updated: 2012-05-15Bibliographically approved
3. The transthyretin-related protein: structural investigation of a novel protein family
Open this publication in new window or tab >>The transthyretin-related protein: structural investigation of a novel protein family
2006 (English)In: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 155, no 3, 445-457 p.Article in journal (Refereed) Published
Abstract [en]

The transthyretin-related protein (TRP) family comprises proteins predicted to be structurally related to the homotetrameric transport protein transthyretin (TTR). The function of TRPs is not yet fully established, but recent data suggest that they are involved in purine catabolism. We have determined the three-dimensional structure of the Escherichia coli TRP in two crystal forms; one at 1.65 A resolution in the presence of zinc, and the other at 2.1 A resolution in the presence of zinc and bromide. The structures revealed five zinc-ion-binding sites per monomer. Of these, the zinc ions bound at sites I and II are coordinated in tetrahedral geometries to the side chains of residues His9, His96, His98, Ser114, and three water molecules at the putative ligand-binding site. Of these four residues, His9, His98, and Ser114 are conserved. His9 and His98 bind the central zinc (site I) together with two water molecules. The side chain of His98 also binds to the zinc ion at site II. Bromide ions bind at site I only, replacing one of the water molecules coordinated to the zinc ion. The C-terminal four amino acid sequence motif Y-[RK]-G-[ST] constitutes the signature sequence of the TRP family. Two Tyr111 residues form direct hydrogen bonds to each other over the tetramer interface at the area, which in TTR constitutes the rear part of its thyroxine-binding channel. The putative substrate/ligand-binding channel of TRP is consequently shallower and broader than its counterpart in TTR.

Place, publisher, year, edition, pages
San Diego: Academic Press, 2006
Keyword
Amino Acid Sequence, Binding Sites, Bromides/metabolism, Crystallography, X-Ray, Escherichia coli Proteins, chemistry, metabolism, Humans, Ligands, Models; Molecular, Molecular Sequence Data, Multigene Family, Prealbumin/*chemistry, Protein Structure; Secondary, Sequence Homology; Amino Acid, Zinc Compounds/metabolism
Identifiers
urn:nbn:se:umu:diva-13601 (URN)10.1016/j.jsb.2006.04.002 (DOI)16723258 (PubMedID)
Available from: 2007-10-12 Created: 2007-10-12 Last updated: 2011-03-15Bibliographically approved
4. Stability and amyloid formation of transthyretin and the transthyretin-related protein
Open this publication in new window or tab >>Stability and amyloid formation of transthyretin and the transthyretin-related protein
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:umu:diva-5047 (URN)
Available from: 2006-04-06 Created: 2006-04-06 Last updated: 2012-06-28Bibliographically approved

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