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Different propensity to form amyloid fibrils by two homologous proteins—Human stefins A and B: Searching for an explanation
Author(s) -
Jenko Saša,
Škarabot Miha,
Kenig Manca,
Gunčar Gregor,
Muševič Igor,
Turk Dušan,
Žerovnik Eva
Publication year - 2004
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.20041
Subject(s) - fibril , monomer , chemistry , crystallography , biophysics , transmission electron microscopy , amyloid (mycology) , amyloid fibril , fiber diffraction , amyloid β , materials science , diffraction , biochemistry , x ray crystallography , polymer , nanotechnology , biology , physics , inorganic chemistry , organic chemistry , optics , medicine , disease , pathology
By using ThT fluorescence, X‐ray diffraction, and atomic force microscopy (AFM), it has been shown that human stefins A and B (subfamily A of cystatins) form amyloid fibrils. Both protein fibrils show the 4.7 Å and 10 Å reflections characteristic for cross β‐structure. Similar height of ∼3 nm and longitudinal repeat of 25–27 nm were observed by AFM for both protein fibrils. Fibrils with a double height of 5.6 nm were only observed with stefin A. The fibril's width for stefin A fibrils, as observed by transmission electron microsopy (TEM), was in the same range as previously reported for stefin B (Žerovnik et al., Biochem Biophys Acta 2002;1594:1–5). The conditions needed to undergo fibrillation differ, though. The amyloid fibrils start to form at pH 5 for stefin B, whereas in stefin A, preheated sample has to be acidified to pH < 2.5. In both cases, adding TFE, seeding, and alignment in a strong magnetic field accelerate the fibril growth. Visual analysis of the three‐dimensional structures of monomers and domain‐swapped dimers suggests that major differences in stability of both homologues stem from arrangement of specific salt bridges, which fix α‐helix (and the α‐loop) to β‐sheet in stefin A monomeric and dimeric forms. Proteins 2004;55:000–000. © 2004 Wiley‐Liss, Inc.