Amyloid-Based Natural Adhesives and Cements - The Functional Fold: Amyloid Structures in Nature - page 134

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principles involved in adhesion. As research into natural adhesives

and cements progresses, similarities in underlying principles have
begun to emerge, while concurrently more variations in the details
becomes clear. This has provided some surprising insights into an
unexpected commonality amongst many adhesives and cements,
as well as emphasizing the multitude of ways that adhesion can be
achieved. This chapter focuses on the identification and mechanical
properties of one such structural commonality between otherwise
unconnected organisms: Functional amyloid .

8.2 Amyloid in Natural Adhesives

The previous chapter (Chapter 7) describes the detection of amyloid
amongst prokaryotes, where

was shown to produce
biofilm-associated amyloid fibrils known as curli.

Escherichia coli

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A specific
functionality was not identified for curli at that time. Curli was
described as a surface protein polymer that mediated interactions
important for biofilm formation, host cell colonization, adhesion,
and cell aggregation.

9,10

) have
since been found to produce other families of amyloid fibrils (see
review of Otzen and Nielsen, 2007),

Several other bacteria (e.g., Salmonella

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and it is believed that multiple
roles exist for amyloid as its widespread occurrence was discovered
in further bacterial species from different habitats.

12,13

Functional amyloid was not identified in natural adhesives until
2006 when a small, green algae,

, was shown to
produce amyloid in the adhesive matrix associated with the holdfast
region that attaches permanently to surfaces in coastal lagoons and
saltmarshes.

Prasiola linearis

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This was the first report of an amyloid-based biological
adhesive and a specific mechanical functionality was associated with
the amyloid component.

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A mechanical response was proposed
relative to the molecular structure of the generic amyloid fibril form
found in natural adhesives using atomic force microscopy (AFM).
The following year, amyloid was found in the adhesive of another
algal species, the filamentous terrestrial green algae

Klebsormidium

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flaccidum Additional characteristics of benefit to the mechanical

properties of the adhesive were revealed, leading to the suggestion
that amyloid fibrils may provide a generic mechanism for mechanical
strength in natural adhesives.

.