PROTEIN SUBUNIT INTERACTIONS AND STRUCTURAL INTEGRITY OF AMYLOIDOGENIC TRANSTHYRETINS - EVIDENCE FROM ELECTROSPRAY MASS-SPECTROMETRY

Wild-type and variant transthyretins form amyloid fibrils in two diffe rent diseases. The biologically active form of transthyretin is a tetr amer but there is evidence that a monomeric species is the amyloidogen ic intermediate. Using mass spectrometry we have developed an approach to monitor the proportions of monomer and tetramer in wild-type and v ariant transthyretins, and found a strong correlation between the inst ability of the tetramer in the gas phase and the amyloidogenicity of t he protein variant. The presence of water molecules in the central cha nnel has been found to be critical for maintaining intact the complex in the gas phase, with additional stability observed in the presence o f excess thyroxine. The solution structure of monomeric transthyretin under fibril-forming conditions was studied using hydrogen exchange mo nitored by mass spectrometry. The results show that Val30Met transthyr etin, the commonest amyloidogenic variant, exhibits loss of hydrogen e xchange protection substantially more rapidly than the wild-type prote in, suggesting partial unfolding of the beta-sheet structure. These re sults provide new insights into the correlation between tetramer stabi lity and amyloidogenicity as well as supporting a possible route to fi bril formation via transient unfolding of the transthyretin monomer. ( C) 1998 Academic Press.