T. Kowalewski et Dm. Holtzman, In situ atomic force microscopy study of Alzheimer's beta-amyloid peptide on different substrates: New insights into mechanism of beta-sheet formation, P NAS US, 96(7), 1999, pp. 3688-3693
Citations number
54
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
We have applied irt situ atomic force microscopy to directly observe the ag
gregation of Alzheimer's beta-amyloid peptide (A beta) in contact with two
model solid surfaces: hydrophilic mica and hydrophobic graphite, The time c
ourse of aggregation was followed by continuous imaging of surfaces remaini
ng in contact with 10-500 mu M solutions of A beta in PBS (pH 7.4). Visuali
zation of fragile nanoscale aggregates of A beta was made possible by the a
pplication of a tapping mode of imaging, which minimizes the lateral forces
between the probe tip and the sample, The size and the shape of A beta agg
regates, as well as the kinetics of their formation, exhibited pronounced d
ependence on the physicochemical nature of the surface. On hydrophilic mica
, A beta formed particulate, pseudo-micellar aggregates, which at higher A
beta concentration had the tendency to form linear assemblies, reminiscent
of protofibrillar species described recently in the literature. In contrast
, on hydrophobic graphite A beta formed uniform, elongated sheets. The dime
nsions of those sheets were consistent with the dimensions of beta-sheets w
ith extended peptide chains perpendicular to the long axis of the aggregate
. The sheets of A beta were oriented along three directions at 120 degrees
to each other, resembling the crystallographic symmetry of a graphite surfa
ce, Such substrate-templated self-assembly may be the distinguishing featur
e of beta-sheets in comparison with alpha-helices. These studies show that
in situ atomic force microscopy enables direct assessment of amyloid aggreg
ation in physiological fluids and suggest that A beta fibril formation may
be driven by interactions at the interface of aqueous solutions and hydroph
obic substrates, as occurs in membranes and lipoprotein particles in vivo.