Spider Silk - The Functional Fold: Amyloid Structures in Nature - page 79

(Fig. 5.3a), which can be assigned to an arrangement, where the
individual β-strands of a β-sheet run perpendicular to the fibre
axis, whereas the sheets are oriented in parallel to the axis.

29,33

The meridional reflection signal thereby represents the main-chain
spacing reflecting the distance between two β-strands (where a
distance of about 9.6 Å was reported to reflect two antiparallel
chains with a marked repeat at the half distance at 4.8 Å), while
the equatorial signal arises from the spacing between two adjacent
β-sheets.

proposed a model where the β-strands
are stacked with turns every eighth amino acid, resulting in a ribbon-
like shape with 25 Å in diameter.

34,35

Geddes et al .

33

a b

c d

Figure 5.3 X-ray diffraction pattern of different silks. (a) Pattern of egg

stalk silk of unstretched, displaying cross-β

structure. 33 (b) Pattern of nanofibrils of a recombinantly
produced spider silk protein displaying cross-β structure 21
(figure taken from Slotta

Chrysopa flava

., 21 copyright Wiley-VCH Verlag
GmbH & Co. KGaA, reproduced with permission). (c) Pattern
of egg stalk silk of

et al

stretched, displaying parallel-β
structure. 33 (a and c: reproduced with permission from
Elsevier.) (d) Pattern of

C. flava

spider silk showing
typical reflection signals for parallel-β structure (figure taken
from: Parkhe

Nephila clavipes

., 36 copyright John Wiley & Sons Limited,
reproduced with permission).

et al