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Aggregation and Metal‐Binding Properties of Mutant Forms of the Amyloid Aβ Peptide of Alzheimer's Disease
Author(s) -
Clements Angela,
Allsop David,
Walsh Dominic M.,
Williams Carvell H.
Publication year - 1996
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1996.66020740.x
Subject(s) - peptide , chemistry , circular dichroism , random coil , amyloid beta , fibril , biophysics , metal ions in aqueous solution , binding site , amyloid (mycology) , metal , crystallography , biochemistry , inorganic chemistry , biology , organic chemistry
The fibrillogenic properties of Alzheimer's Aβ peptides corresponding to residues 1–40 of the normal human sequence and to two mutant forms containing the replacement Ala 21 to Gly or Glu 22 to Gln were compared. At pH 7.4 and 37°C the Gln 22 peptide was found to aggregate and precipitate from solution faster than the normal Aβ, whereas the Gly 21 peptide aggregated much more slowly. Electron microscopy showed that the aggregates all had fibrillar structures. Circular dichroism spectra of these peptides revealed that aggregation of the normal and Gln 22 sequences was associated with spectral changes consistent with a transformation from random coil to β sheet, whereas the spectrum of the Gly 21 peptide remained almost unchanged during a period in which little or no aggregation occurred. When immobilised by spotting onto nitrocellulose membranes the peptides bound similar amounts of the radioisotope 65 Zn 2+ . Of several competing metal ions, tested at 20× the concentration of Zn 2+ , Cu 2+ displaced >95% of the radioactivity from all three peptides and Ni 2+ produced >50% displacement in each case. Some other metal ions tested caused lesser displacement, but Fe 2+ and Al 3+ were without effect. In a saturation binding assay, a value of 3.2 µ M was obtained for the binding of Zn 2+ to Aβ but our data provided no evidence for a reported higher affinity site (107 n M ). The results suggest that the neuropathology associated with the Gly 21 mutation is not due to enhanced fibrillogenic or different metal‐binding properties of the peptide and that the binding of zinc to amyloid peptides is not a specific phenomenon.