Proteolytic cleavage of Ser52Pro variant transthyretin triggers its amyloid fibrillogenesis.
The Ser52Pro variant of transthyretin (TTR) produces aggressive, highly penetrant, autosomal-dominant systemic amyloidosis in persons heterozygous for the causative mutation. Together with a minor quantity of full-length wild-type and variant TTR, the main component of the ex vivo fibrils was the residue 49-127 fragment of the TTR variant, the portion of the TTR sequence that previously has been reported to be the principal constituent of type A, cardiac amyloid fibrils formed from wild-type TTR and other TTR variants [Bergstrom J, et al. (2005) J Pathol 206(2):224-232]. This specific truncation of Ser52Pro TTR was generated readily in vitro by limited proteolysis. In physiological conditions and under agitation the residue 49-127 proteolytic fragment rapidly and completely self-aggregates into typical amyloid fibrils. The remarkable susceptibility to such cleavage is likely caused by localized destabilization of the β-turn linking strands C and D caused by loss of the wild-type hydrogen-bonding network between the side chains of residues Ser52, Glu54, Ser50, and a water molecule, as revealed by the high-resolution crystallographic structure of Ser52Pro TTR. We thus provide a structural basis for the recently hypothesized, crucial pathogenic role of proteolytic cleavage in TTR amyloid fibrillogenesis. Binding of the natural ligands thyroxine or retinol-binding protein (RBP) by Ser52Pro variant TTR stabilizes the native tetrameric assembly, but neither protected the variant from proteolysis. However, binding of RBP, but not thyroxine, inhibited subsequent fibrillogenesis.
Wolfson Drug Discovery Unit, Centre for Amyloidosis and Acute Phase Proteins, Division of Medicine, Laboratory of Protein Crystallography, Centre for Amyloidosis and Acute Phase Proteins, and Electron Microscopy Unit, University College London, London NW3 2PF, United Kingdom.
P Patrizia
PP
Mangione
Riccardo
R
Porcari
Julian D
JD
Gillmore
Piero
P
Pucci
Maria
M
Monti
Mattia
M
Porcari
Sofia
S
Giorgetti
Loredana
L
Marchese
Sara
S
Raimondi
Louise C
LC
Serpell
Wenjie
W
Chen
Annalisa
A
Relini
Julien
J
Marcoux
Innes R
IR
Clatworthy
Graham W
GW
Taylor
Glenys A
GA
Tennent
Carol V
CV
Robinson
Philip N
PN
Hawkins
Monica
M
Stoppini
Stephen P
SP
Wood
Mark B
MB
Pepys
Vittorio
V
Bellotti
D000595:Amino Acid Sequence; D000682:Amyloid / Q000378:metabolism*; D000686:Amyloidosis / Q000235:genetics / Q000473:pathology; D018360:Crystallography, X-Ray; D006801:Humans; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010641:Phenotype; D011228:Prealbumin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011392:Proline / Q000378:metabolism*; D059748:Proteolysis; D012694:Serine / Q000378:metabolism*
D000682:Amyloid; D011228:Prealbumin; D012694:Serine; D011392:Proline
misfolding; protein aggregation