X-ray scattering by bundles of cylinders

Glucagon Fibril Polymorphism Reflects Differences in Protofilament Backbone Structure

“…The diffraction pattern from straight fibers as a function of scattering vector q was fitted to the following expression based on the diffraction pattern expected from a plane wave incident on a cylinder: 67,68 …”

Synchrotron X-ray studies suggest that the core of the transthyretin amyloid fibril is a continuous β-sheet helix

“…The classic cross-␤ X-ray pattern of amyloid has a single 10 Å maximum on the equator, interpreted as representing the spacing of ␤ sheets perpendicular to the fibril axis, whereas the equatorials observed from the X-ray patterns of FAP contain a number of diffraction maxima (Table 2). As shown in Table 2, the spacings of the equatorials can be interpreted in terms of 'non-Bragg maxima' arising from short-range lateral order within amyloid fibrils [22,23] that are composed of protofilaments with a centre-to-centre spacing of 64 Å, as observed in electron micrographs [13].…”

“…The unit-cell parameters, the positions of the reflections and their relative intensities were used to assign a space group and predict the contents of the unit cell. The equatorial reflections could be indexed to a cell of 64 Å and could be interpreted in terms of 'non-Bragg maxima' arising from short-range lateral order within the amyloid fibrils [22,23].…”

The molecular basis of amyloidosis

“…perpendicular to the fibre axis, the reflections will be of the non-Bragg type. Burge [15,16] has shown that for the pseudo-hexagonally close-packed fibres, the spacing of the equatorial reflections can be described by zero-order Bessel functions, dependent only on the average centre-to-centre spacing of the fibrils. The intensities of these reflections will then be related to the molecular transform of the radial electron-density distribution of an individual fibril.…”

“…The equatorial reflections observed from the X-ray patterns of Val30Met transthyretin fibrils contain a number of diffraction maxima (table 3). The spacings of the equatorial reflections can be interpreted in terms of 'non-Bragg maxima' arising from short-range lateral order within the amyloid fibrils [15] composed of protofilaments with a centre-to-centre spacing of 65 Å observed in electron micrographs [8]. The intensities of the equatorial reflections can be interpreted as arising from the overall molecular structure of the protofilaments as projected down their long axis.…”