Spider Silk - The Functional Fold: Amyloid Structures in Nature - page 74

5.1 Introduction

Functional amyloids are typically secreted or extruded structural
proteins which exist in various animal kingdoms like bacteria, fungi,
invertebrates, and vertebrates. Besides its presence in functional
amyloids, it is proposed that the amyloid structure represents a
generic conformational state which can under certain circumstances
be adopted by any polypeptide chain.

1,2

In this article, we focus on typically non-amyloidogenic proteins,
namely silk, a class of structural proteins solely produced by
arthropods. Many different types of silks are known, each displaying
distinct mechanical properties which are perfectly adapted to their
application ranging from protection to reproduction purposes and
capturing prey. Most arthropods can produce only one type of silk,
whereas orb weaving spiders are able to produce up to 6 different
kinds of silk and a glue substance (Fig. 5.1).

Figure 5.1 Different silks produced by a female orb weaving spider. Each is

adapted perfectly to its purpose mainly regarding mechanical
properties. The two major and best investigated silks are
dragline silk and flagelliform silk. The dragline is a tough fibre
forming frame and radii of the web, additionally serving as
lifeline when the spider drops. Flagelliform silk is more elastic
to dissipate the impact energy of flying prey. Adapted and
reproduced from Romer and Scheibel, 3 with permission from
Landes Bioscience. See also Colour Insert.

5.2 Overview of Silk Structure, Mechanics,

and Assembly

The basic components of silks are specific proteins, typically stored
in distinct glands which have evolved from one single type of gland.

4

Various silks reveal different structures as summarized in Table 5.1
(modified from Craig

5

).