Fig. 2.

X-ray fiber diffraction image from partially aligned apoA1 fibrils. The cross-β reflections characteristic of amyloid fibrils are visible at 4.81 Å on the meridian and at 9.35 and 11.82 Å on the equator. The meridional reflection arises from the interstrand spacing between β-strands, lying at right angles to the fibril long axis. The two weaker and more diffuse equatorial reflections are a consequence of the intersheet spacing and close lateral packing of fibrils. In addition to these reflections, there are strong and sharp reflections at 5.08 and 2.54 Å on the equator, suggestive of the presence of well-defined coiled coil structure, preferentially aligned with the direction of hydrogen bonding at right angles to the fibril long axis.