Silkmoth Chorion: A Natural Protective Amyloid - The Functional Fold: Amyloid Structures in Nature - page 63

Figure 4.9 X-ray diffraction pattern from an oriented fibre of cA peptide

amyloid-like fibrils. The meridian, M (direction parallel to the
fibre axis) is horizontal and the equator, E, is vertical in this
display. The X-ray diffraction pattern is a typical “cross- ”

pattern showing a 4.66 Å reflection on the meridian and a
10.12 Å reflection on the equator. This indicates a regular
structural repeat of 4.66 Å along the fibre axis (meridian) and
a structural spacing of 10.12 Å perpendicular to the fibre axis.
The structural repeat of 4.66 Å along the fibre axis corresponds
to the spacing of adjacent

β

-strands (which should be
perpendicular to the fibre axis, a “cross-

β

” structure), and the
10.12 Å spacing perpendicular to the fibre axis corresponds to
the face-to-face separation (packing distance) of the

β

β

-sheets.

In addition, the FT-Raman and ATR FT-IR spectra of cA peptide
amyloid fibrils, cast on a Au mirror (Fig. 4.10), clearly suggest that
β

-sheets are present in the structure of the cA peptide amyloid
fibrils,

23

β

and, furthermore, that the -sheets are antiparallel

18,24
Further, we have designed and synthesized peptides with lengths
equal to fractions of the length of the cA peptide. Thus, a 24-residue
peptide was synthesized,

− 1

(shoulder at 1692 cm in the amide I band).

9

along with peptides of 12-residues and
6-residues in length (Iconomidou and Hamodrakas, in preparation).
All these peptides fold and self-assemble, forming amyloid fibrils
almost identical in structure and properties to the fibrils formed by
the cA peptide. This clearly suggests that amyloid fibril formation