Question

Compare and contrast the mechanism of transthyretin-mediated thyroxine and retinol transport.

Answer 1

Transthyretin (TTR) is a protein of thyroxine-binding globulin and albumin found in plasma and cerebrospinal fluid. TTR gene on 18th chromosome encodes the transthyretin. It is secreted into plasma by liver and choroid plexus secretes TTR into the cerebrospinal fluid. It acts a main carrier of thyroid hormone T4 to brain an also indirectly implicated in the carriage of vitamin A via retinol-binding protein (RBP). It was identified in 1942 as pre-albumin since it migrates faster than serum albun in gel electrophoresis. In blood, less than 1% of TTR's T4 binding sites are actually occupied. Monomeric TTR is a 127-residue polypeptide and TTR is 55kDa homotetramer. Binding of two dimers in a face-to-face fashion enable the bindong of two thyroxine binding sites per tetramer. TTR found to have lower binding strength but abundant in plasma.