Thyroid hormone-binding protein. Probably transports thyroxine from the bloodstream to the brain. Homotetramer. Dimer of dimers. In the homotetramer, subunits assemble around a central channel that can accommodate two ligand molecules. Interacts with RBP4. Detected in serum and cerebrospinal fluid (at protein level). Highly expressed in choroid plexus epithelial cells. Detected in retina pigment epithelium and liver. Each monomer has two 4-stranded beta sheets and the shape of a prolate ellipsoid. Antiparallel beta-sheet interactions link monomers into dimers. A short loop from each monomer forms the main dimer-dimer interaction. These two pairs of loops separate the opposed, convex beta-sheets of the dimers to form an internal channel. Not glycosylated under normal conditions. Following unfolding, caused for example by variant AMYL-TTR 'Gly-38', the cryptic Asn-118 site is exposed and glycosylated by STT3B-containing OST complex, leading to its degradation by the ER-associated degradation (ERAD) pathway. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Tetramer dissociation and partial unfolding leads to the formation of aggregates and amyloid fibrils. Small molecules that occupy at least one of the thyroid hormone binding sites stabilize the tetramer, and thereby stabilize the native state and protect against misfolding and the formation of amyloid fibrils. Two binding sites for thyroxine are located in the channel. Less than 1% of plasma prealbumin molecules are normally involved in thyroxine transport. L-thyroxine binds to the transthyretin by an order of magnitude stronger than does the triiodo-L-thyronine. Thyroxine-binding globulin is the major carrier protein for thyroid hormones in man. About 40% of plasma transthyretin circulates in a tight protein-protein complex with the plasma retinol-binding protein (RBP). The formation of the complex with RBP stabilizes the binding of retinol to RBP and decreases the glomerular filtration and renal catabolism of the relatively small RBP molecule. There is evidence for 2 binding sites for RBP, one possibly being a region that includes Ile-104, located on the outer surface of the transthyretin molecule. Belongs to the transthyretin family. Transthyretin entry