The tetrameric protein transthyretin dissociates to a non-native monomer in solution. A novel model for amyloidogenesis.
In amyloidosis, normally innocuous soluble proteins polymerize to form insoluble fibrils. Amyloid fibril formation and deposition have been associated with a wide range of diseases, including spongiform encephalopathies, Alzheimer's disease, and familial amyloid polyneuropathies (FAP). In certain forms of FAP, the amyloid fibrils are mostly constituted by variants of transthyretin (TTR), a homotetrameric plasma protein implicated in the transport of thyroxine and retinol. The most common amyloidogenic TTR variant is V30M-TTR, and L55P-TTR is the variant associated with the most aggressive form of FAP. Recently, we reported that TTR dissociates to a monomeric species at pH 7.0 and nearly physiological ionic strengths (Quintas, A., Saraiva, M. J., and Brito, R. M. (1997) FEBS Lett. 418, 297-300). Here, we show that the tetramer dissociation is apparently irreversible; and based on intrinsic tryptophan fluorescence and fluorescence quenching experiments, we show that the monomeric species formed upon tetramer dissociation is non-native. We also show, based on 1-anilino-8-naph-thalenesulfonate binding studies, that this monomeric species appears not to behave like a molten globule. These data allowed us to propose a model for TTR amyloidogenesis based on tetramer dissociation occurring naturally under commonly observed physiological solution conditions.
Quintas
A
A
Centro de Neurociências de Coimbra, Universidade de Coimbra, 3004-517 Coimbra, Portugal.
Saraiva
M J
MJ
Brito
R M
RM
D000682:Amyloid / Q000737:chemistry*; D017772:Amyloid Neuropathies / Q000235:genetics*; D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D002850:Chromatography, Gel; D019791:Guanidine / Q000494:pharmacology; D006801:Humans; D007454:Iodides / Q000494:pharmacology; D008958:Models, Molecular; D011228:Prealbumin / Q000737:chemistry*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D012995:Solubility; D013050:Spectrometry, Fluorescence; D014364:Tryptophan
D000682:Amyloid; D000817:Anilino Naphthalenesulfonates; D007454:Iodides; D011228:Prealbumin; D011994:Recombinant Proteins; C027132:1-anilino-8-naphthalenesulfonate; D014364:Tryptophan; D019791:Guanidine