Probing Solvent Accessibility of Transthyretin Amyloid by Solution NMR Spectroscopy

The human plasma protein transthyretin (TTR) may form fibrillar protein deposits that are associated with both inherited and idiopathic amyloidosis. The present study utilizes solution nuclear magnetic resonance spectroscopy, in combination with hydrogen/deuterium exchange, to determine residue-specific solvent protection factors within the fibrillar structure of the clinically relevant variant, TTRY114C. This novel approach suggests a fibril core comprised of the six β-strands, A-B-E-F-G-H, which retains a native-like conformation. Strands C and D are dislocated from their native edge region and become solvent-exposed, leaving a new interface involving strands A and B open for intermolecular interactions. Our results further support a native-like intermolecular association between strands F-F′ and H-H′ with a prolongation of these β-strands and, interestingly, with a possible shift in β-strand register of the subunit assembly. This finding may explain previous observations of a monomeric intermediate preceding fibril formation. A structural model based on our results is presented.