Transthyretin (TTR) is a thyroid hormone-binding protein present in the plasma and/or cerebrospinal fluid of vertebrates. Transthyretin is a multifunctional protein. It distributes thyroid hormones in blood and indirectly transports vitamin A via binding to retinol-binding protein (RBP) [, , ]. It also has proteolytic activity [, ]. For instance, TTR can cleave apoA-I, the major HDL apolipoprotein []. Transthyretin exists mainly as a homotetramer, with each subunit largely arranged into a β-sheet structure. Transthyretin is implicated in human amyloid diseases [, ].
