PDBsum entry 1tyr

Retinol-binding

PDB id: 1tyr

Contents

Protein chain

127 a.a. *

Ligands

9CR ×2

Waters ×97

* Residue conservation analysis

PDB id:

1tyr

Name:

Retinol-binding

Title:

Transthyretin complex with retinoic acid

Structure:

Transthyretin. Chain: a, b. Synonym: prealbumin

Source:

Homo sapiens. Human. Organism_taxid: 9606

Biol. unit:

Dimer (from PQS)

Resolution:

1.80Å R-factor: 0.196

Authors:

G.Zanotti,M.R.D'Acunto,G.Malpeli,C.Folli,R.Berni

Key ref:

G.Zanotti et al. (1995). Crystal structure of the transthyretin--retinoic-acid complex. Eur J Biochem, 234, 563-569. PubMed id: 8536704

Date:

12-May-95 Release date: 15-Sep-95

Protein chains

P02766  (TTHY_HUMAN) -  Transthyretin from Homo sapiens

Seq: 147 a.a.

Struc: 127 a.a.

Eur J Biochem 234:563-569 (1995)

PubMed id: 8536704

Crystal structure of the transthyretin--retinoic-acid complex.

G.Zanotti, M.R.D'Acunto, G.Malpeli, C.Folli, R.Berni.

ABSTRACT

Retinoids are quite insoluble and chemically unstable compounds in the aqueous medium, such that natural retinoids need to be bound to specific retinoid-binding proteins to be protected, solubilized and transported in body fluids. All-trans retinoic acid exhibits a relatively high affinity for thyroxine-binding transthyretin in vitro and this protein is a good candidate for the transport of retinoic acid administered as pharmacological or antitumor agent. To define structural features essential for the recognition by transthyretin of a ligand which is structurally unrelated to thyroxine, we have cocrystallized human transthyretin with retinoic acid and determined its structure at 0.18-nm resolution. The retinoid fits into the two chemically identical thyroxine-binding sites, which are located in the central channel that runs through the tetrameric transthyretin. The cyclohexene ring of the bound retinoid is innermost, occupying the same position of the phenolic ring of the bound 3,3'-diiodo-L-thyronine, whereas the carboxylate group, like the same group of the thyroid hormone, participates in an ionic interaction with the Lys15 side chain at the entrance of the channel. Despite the fact that transthyretin was cocrystallized with all-trans-retinoic acid, the isoprene chain of the bound retinoid has been found in a non-extended conformation. This feature, that allows the carboxylate to orient in a manner suitable for ion-pair association with the Lys15 side chain, is attributable to the conversion of all-trans-retinoic acid into cis-isomers or folded conformers. It is concluded that the presence, in an essentially hydrophobic molecular core of the appropriate size, of a negatively charged group at the correct position is a crucial requirement for ligand-transthyretin recognition. Whereas the binding of the ligand has no remarkable consequences for the protein structure, all-trans-retinoic acid undergoes structural changes such as to interact favorably with residues present in the thyroxine-binding sites, resembling roughly the natural ligand.