Oligomers and beaded APFs
The first method of evaluating the sizes of the beads was to copy
individual images of isolated beads in both bAPF and sAPF micrographs,
classify them according to their sizes, superimpose the images in each
category, and then use image averaging to obtain a single image for each
size (first two rows of Fig. 2). We identified five sizes of beads. The
major difficulty with this method is that the outer perimeter is not
clear cut. Although isolated images of the smallest category were
difficult to identify in the bAPF micrograph, they were prevalent in
some sAPF micrographs.
The second method was to approximate distances between beads of bAPFs.
We first identified relatively symmetric bAPF composed of the same size
of beads. We used rotational image averaging to obtain symmetric
averaged images, and then superimposed images of the same size and shape
to obtain a single averaged image. We excluded bAPFs from the analysis
if they were relatively asymmetric, had substantial gaps between beads,
were composed of different sized beads, contained beads that appear to
have merged, and/or had an ambiguous number of beads. The advantage of
this approach is that the diameter of the beads can be approximated from
the distance between the centers of adjacent beads, which can be
measured more precisely than the location of the outer edges of isolated
beads. The remaining rows in Fig. 2 are images of assemblies of 2-10
beads. Sizes of the beads are color coded as in the first two rows.