Transthyretin

Transthyretin (TTR) is a serum and cerebrospinal fluid carrier of the thyroid hormone thyroxine (T₄) and retinol-binding protein bound to retinol. This is how transthyretin gained its name, transports thyroxine and retinol. The liver secretes transthyretin into the blood, and the choroid plexus secretes TTR into the cerebrospinal fluid.

TTR was originally called prealbumin (or thyroxine-binding prealbumin) because it ran faster than albumin on electrophoresis gels.

Binding affinities

It functions in concert with two other thyroid hormone-binding proteins in the serum:

In cerebrospinal fluid TTR is the primary carrier of T₄. TTR also acts as a carrier of retinol (vitamin A) through its association with retinol-binding protein (RBP) in the blood and the CSF. Less than 1% of TTR's T₄ binding sites are occupied in blood, which is taken advantage of below to prevent TTRs dissociation, misfolding and aggregation which leads to the degeneration of post-mitotic tissue.

Numerous other small molecules are known to bind in the thyroxine binding sites, including many natural products (such as resveratrol), drugs (Tafamidis, or Vyndaqel, diflunisal,flufenamic acid), and toxins (PCB).