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folded this way (Fig. 4.12b). Another attractive feature of the left-
handed parallel
-helix model is the hydrophobic faces of the
triangular prism-like
β
β
-helix (Fig. 4.12b). Nevertheless, the “edges”
of this prism are occupied by charged, polar residues and glycines,
and this makes 3-D packing difficult, unless there are very specific
interactions. In contrast, the hydrophobic faces of the antiparallel
β
-sheet structure shown in Fig. 4.12 facilitate uniform 3-D packing of
the
β
-sheets, leaving the polar and charged residues on both lateral
“edges” of the sheet for favourable lateral interactions.
To our knowledge, we proposed the first structural model
at atomic resolution for a left-handed parallel
β
-helix structure
5
underlying amyloid fibrils.
-helices in the amyloid
fibrillar structure was later further described by several other
groups.
The existence of
β
4,36-41
-pleated sheet model
shown in Fig. 4.11, as the prevalent structure present in amyloid
fibrils formed from peptide-analogues of silkmoth chorion proteins
is provided by the following: (i) preliminary calculations of X-ray
diffraction patterns from the models presented in Figs. 4.11 and
4.12 and comparison with the experimental diffraction pattern of
Fig. 4.8 (data not shown); (ii) analysis of the amide I band of FT-
Raman spectra (Fig. 4.10; data not shown); (iii) the presence of the
high frequency component in the 1690-1700 cm
Clear support to the antiparallel twisted
β
1
in the ATR FT-IR
spectra (Fig. 4.10) taken from samples containing amyloid-like fibrils
formed from all, similar to natural, chorion peptides synthesized
so far.
4.4 
Silkmoth Chorion: A Natural 
Protective Amyloid
We have shown that cA-peptide fibrils have an amyloid nature, as
well as all the other synthesized peptide-analogues of silkmoth
chorion proteins, but we have so far silently assumed that the
peptide fibrils are truly representative of the structure of chorion
proteins in the eggshell. The cA peptide itself alone corresponds to
approximately 25-30% of the total chorion mass. Its self-assembly
mechanisms produce amyloid-like fibrils under a diverse variety of
conditions, which strongly suggests that it should fold in an amyloid
fashion in the physiological state, also
in vivo
. Concomitant evidence
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