Prealbumin (TTR) Human Native Protein

This gene encodes transthyretin, one of the three prealbumins including alpha-1-antitrypsin, transthyretin and orosomucoid. Transthyretin is a carrier protein; it transports thyroid hormones in the plasma and cerebrospinal fluid, and also transports retinol (vitamin A) in the plasma. The protein consists of a tetramer of identical subunits. More than 80 different mutations in this gene have been reported; most mutations are related to amyloid deposition, affecting predominantly peripheral nerve and/or the heart, and a small portion of the gene mutations is non-amyloidogenic. The diseases caused by mutations include amyloidotic polyneuropathy, euthyroid hyperthyroxinaemia, amyloidotic vitreous opacities, cardiomyopathy, oculoleptomeningeal amyloidosis, meningocerebrovascular amyloidosis, carpal tunnel syndrome, etc. [provided by RefSeq]

Function: Thyroid hormone-binding protein. Probably transports thyroxine from the bloodstream to the brain. Ref.29

Subunit structure: Homotetramer. Dimer of dimers. In the homotetramer, subunits assemble around a central channel that can accomodate two ligand molecules. Interacts with RBP4. Ref.41 Ref.44 Ref.45 Ref.50 Ref.53 Ref.54

Subcellular location: Secreted. Cytoplasm Ref.9 Ref.29.

Tissue specificity: Detected in serum and cerebrospinal fluid (at protein level). Highly expressed in choroid plexus epithelial cells. Detected in retina pigment epithelium and liver. Ref.9 Ref.29

Domain: 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.

Involvement in disease: Defects in TTR are the cause of amyloidosis transthyretin-related (AMYL-TTR) [

MIM:105210]. A hereditary generalized amyloidosis due to transthyretin amyloid deposition. Protein fibrils can form in different tissues leading to amyloid polyneuropathies, amyloidotic cardiomyopathy, carpal tunnel syndrome, systemic senile amyloidosis. The disease includes leptomeningeal amyloidosis that is characterized by primary involvement of the central nervous system. Neuropathologic examination shows amyloid in the walls of leptomeningeal vessels, in pia arachnoid, and subpial deposits. Some patients also develop vitreous amyloid deposition that leads to visual impairment (oculoleptomeningeal amyloidosis). Clinical features include seizures, stroke-like episodes, dementia, psychomotor deterioration, variable amyloid deposition in the vitreous humor. Ref.5 Ref.6 Ref.17 Ref.18 Ref.19 Ref.20 Ref.22 Ref.23 Ref.35 Ref.36 Ref.39 Ref.45 Ref.46 Ref.50 Ref.52 Ref.55 Ref.65 Ref.66 Ref.68 Ref.69 Ref.70 Ref.72 Ref.74 Ref.75 Ref.76 Ref.77 Ref.78 Ref.79 Ref.80 Ref.81 Ref.82 Ref.83 Ref.84 Ref.85 Ref.86 Ref.87 Ref.88 Ref.89 Ref.90 Ref.92 Ref.93 Ref.94 Ref.96 Ref.97 Ref.98 Ref.99 Ref.100 Ref.101 Ref.102 Ref.103 Ref.104 Ref.107 Ref.108 Ref.109 Ref.111 Ref.112 Ref.113 Ref.114 Ref.115 Ref.116 Ref.117 Ref.118 Ref.119 Ref.120 Ref.122 Ref.123 Ref.124 Ref.125 Ref.126 Ref.127 Ref.128Defects in TTR are a cause of hyperthyroxinemia dystransthyretinemic euthyroidal (HTDE) [

MIM:145680]. It is a condition characterized by elevation of total and free thyroxine in healthy, euthyroid persons without detectable binding protein abnormalities. Ref.26Defects in TTR are a cause of carpal tunnel syndrome type 1 (CTS1) [

MIM:115430]. It is a condition characterized by entrapment of the median nerve within the carpal tunnel. Symptoms include burning pain and paresthesias involving the ventral surface of the hand and fingers which may radiate proximally. Impairment of sensation in the distribution of the median nerve and thenar muscle atrophy may occur. This condition may be associated with repetitive occupational trauma, wrist injuries, amyloid neuropathies, rheumatoid arthritis. Ref.95

Miscellaneous: 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.

Sequence similarities: Belongs to the transthyretin family.