Silkmoth Chorion: A Natural Protective Amyloid - The Functional Fold: Amyloid Structures in Nature - page 69

for this assumption can be found in Fig. 4.3. Lamellae (layers) of
fibrils with the same dimensions (approximately 100 Å; see also
refs. 10 and 11) as the cA peptide double-helical fibrils shown in
Figs. 4.8 and 4.9 constitute the helicoidal architecture of silk moth
chorion. Chorion fibrils consist of 30-40 Å protofilaments with
a helical structure (ref. 12 and references therein). Furthermore,
antiparallel -pleated sheet is the dominant molecular conformation

of silk moth chorion proteins

β

(ref. 12 and references therein;
Figs. 4.4-4.6). In addition, silkmoth chorion binds Congo red
showing the characteristic red-green/yellow birefringence when
seen under crossed polars (Fig. 4.13). This strengthens our proposal
that silkmoth chorion is a natural protective amyloid.
Amyloids are generally associated with diseases such as
Alzheimer's, spongiform encephalopathies, and type II diabetes
etc. More than 20 types of human diseases are associated with the
deposition of protein fibrils forming amyloid and resulting in tissue
damage and degeneration.

in vivo

1,2

Amyloidogenic proteins appear to be
related by their ability to undergo a conformational change and
adopt a new amyloidogenic conformation under partially denaturing
conditions

42,43

in vivo , which permits self-assembly into amyloid.

Our studies were the first to show that not all amyloids are, by
definition harmful.

5

In chorion protein amyloids, the amyloidogenic
conformation is, apparently, the native conformation.

a b

Figure 4.13 Photomicrographs of a part of a silkmoth chorion from Bombyx

mori stained with Congo red: (a) bright field illumination, (b)

crossed polars. The red-green/yellow birefringence character-
istic for amyloids is clearly seen. Bar = 400

µ

m. See also Colour

Insert.