Deuterium-proton exchange on the native wild-type transthyretin tetramer identifies the stable core of the individual subunits and indicates mobilityat the subunit interface

Transthyretin is a human protein capable of amyloid formation that is belie ved to cause several types of amyloid disease, depending on the sequence de posited. Previous studies have demonstrated that wild-type transthyretin (T TR), although quite stable, forms amyloid upon dissociation from its native tetrameric form into monomers with an altered conformation. Many naturally occurring single-site variants of TTR display decreased stability in vitro , manifested by the early onset familial amyloid diseases in vivo. Only sub tle structural changes were observed in X-ray crystallographic structures o f these disease associated variants. In this study, the stability of the wi ld-type TTR tetramer was investigated at the residue-resolution level by mo nitoring H-2-H exchange via NMR spectroscopy. The measured protection facto rs for slowly-exchanging amide hydrogen atoms reveal a stable core consisti ng of strands A, B, E, F, and interestingly, the loop between strands A and B. Ln addition, the faster exchange of amide groups from residues at the s ubunit interfaces suggests unexpected mobility in these regions. This infor mation is crucial for future comparisons between disease-associated and wil d-type tetramers. Such studies can directly address the regions of TTR that become destabilized as a consequence of single amino acid substitutions, p roviding clues to aspects of TTR amyloidogenesis. (C) 2000 Academic Press.