Spider Silk - The Functional Fold: Amyloid Structures in Nature - page 85

16
In this model, a structural recon�iguration after �ibril formation
would be necessary to yield a parallel-β structure, probably through
shear forces and stretching (see earlier in text). However, the process
of �ibril formation as known from various amyloid structures is
a quite slow process. Therefore, it seems very unlikely that the
rapid thread formation during spinning is consistent with such an
assembly pathway.

have been described at the transition of the B-zone into the duct.

a

b

c

Figure 5.4 Potential assembly pathways towards silk thread formation

(a and b) and self-assembly resulting in amyloid-like �ibrils (c).
(a) The micelle theory; 17,19,61,63 (b) the liquid-crystal spinning
theory proposed by Vollrath; 4 (c) the nucleation-aggregation
mechanism leading to the formation of amyloid �ibrils. 21 Figure
adapted from Slotta. 73

5.3 Conclusion

70

The amyloid fold is thought to be a very ancient structure , very

likely not restricted to speci�ic proteins. Moreover, it is suggested to
be an intrinsic property of polypeptide backbones in general, with
hydrogen bonds being the predominant driving force for forming
amyloid structures.

71

Nature might have taken advantage of this
highly stable fold, and proteins evolved adopting this structure for
speci�ic structural and mechanical functions.

71,72