Table 1.

Interpretation of amyloid structures

Protein fiber	Experimental method	Experimental findings	Suggested interpretation	Reference
Alzheimer extracellular Aβ plaques, residues 11–25 fragment	X-ray diffraction and computed reconstruction from electron micrographs	All fibers give a strong 4.75-Å meridional x-ray reflection. Small angle reflections were not recorded. Optical reconstruction shows cylinders of 57 Å diameter with 37-Å-thick walls surrounding a central hole of 19.5 Å diameter. It also shows β-strands clearly stacked 4.75 Å apart with their length normal to the fiber axis	Two concentric cylinders of β-sheets, the chains run normal to the fiber axis as in the reconstruction; calculated fiber diameter 60 Å	7
Alzheimer extracellular Aβ variant, residues 11–25 with Asp-23 → Lys substitution	Electron microscopy and x-ray diffraction	Fibers of 35–40 Å diameter. Strong 4.75-meridional and extremely weak 10-Å equatorial reflexions	Single cylindrical β-sheet made of two 14-residue peptides arranged in tandem in a circle, giving a calculated fiber diameter of 40 Å	8
Synuclein deposits in Parkinson's disease and synthetic fibers of wild-type synuclein	Electron microscopy and electron diffraction	Filaments 60–90 Å wide that give only the strong 4.75-Å meridional reflexion and its second order, and a very weak equatorial 10-Å reflexion	Rods made of single cylindrical shells of helically wound β-strands forming dimers or trimers	2
Human transthyretin variant Val-30 → Met	X-ray diffraction	Meridional reflections indexed as orders of 115 Å; very strong reflexion at 4.83 Å, strong reflexion at 4.65 Å, suggesting sampling of transform with peak at 4.75 Å. Strong equatorial reflexion at 64 Å, medium ones at 12.6 and 10.1 Å, suggesting sampling of peak at 10.9 Å	Possibly two protofibrils of 32 Å diameter wound around each other with a 115-Å repeat	17