Amyloid-Based Natural Adhesives and Cements - The Functional Fold: Amyloid Structures in Nature - page 140

or “fingerprints” is unproven. Such terms may only be valid for
synthesized or purified single component systems. The underlying
mechanism responsible for the strength of a natural adhesive can
thus be deduced from the characteristic mechanical properties
of the constituent molecules, rather than from the biochemical
identification of specific molecules present.

a

600

b

400

200

0

-200

0 500 1000

Extension (nm)

Figure 8.4 Nanoscale mechanical unfolding of amyloid fibril β-sheets in

algal adhesive. (a) A representative AFM force-extension curve
from holdfasts of the green alga , showing highly

ordered sawtooth structures. (b) Schematic model of the
mechanical manipulation of a single intermolecular β-sheet
(pink) at the surface of an amyloid fibril (green) by an AFM tip.
The schematic shows interacting molecular building blocks of
intramolecular β-sheets running perpendicular to the direction
of the fibril making up extended intermolecular β-sheets that
form the fibril. The “hidden length” is contained within the
folds of each individual monomer (detail is shown only below
the tip) and the “sacrificial bonds” exist between these folds.
Interactions between the monomers must be significantly
stronger than these sacrificial bonds and imply cross-linking
between each individual protein, as indicated with the solid line
running along the back of the manipulated intermolecular β-
sheet. With kind permissio n from Springer Science + Business
Media:

P . linearis

, Nanoscale mechanical
characterisation of amyloid fibrils discovered in a natural
adhesive,

Journal of Biological Physics

(2006) 393-401, A. S. Mostaert, M. J. Higgins, T.
Fukuma, F. Rindi, S. P. Jarvis, figures 2(a), 5. 14 See also Colour
Insert.

32

The repetitive sawtooth response can be quantitatively analysed
using the worm-like chain model for polymers

36,38

that provides,
amongst other parameters, a persistence length. In the case of
pulling apart the protein monomer constituents of an amyloid fibril,
the persistence length approximates the size of an amino acid (this