Page 276 - Advances in Textile Biotechnology

Developments in recombinant silk and other elastic protein fi bers 257

10.7.4 Resilin

Resilin is a structural protein with elastomeric properties, which is repre-
sented in specialized regions of the cuticle of most insects, where it is known

to play important roles in insect flight, the jumping mechanisms of fl eas, and
vocalization in cicadas (Kim et al., 2007). Naturally crosslinked resilin exhib-
its two outstanding material properties: high resilience (recovery after
deformation), of 92%, resilin can be stretched three or four times its resting
length before breaking, and can return to its original resting shape with very
little deformation, and a very high fatigue lifetime. This performance is far
superior to that of a known low resilience rubber, chlorobutyl rubber (56%),
and even to that of high-resilience polybutadiene rubber (80%). Stress–
strain data show it to have a modulus at 100% of about 2.5 kPa, consider-

ably below that of typical unfilled synthetic elastomers and native elastin
(Elvin et al., 2005).
To date, partly because of diffi culties in obtaining large amounts of pure
resilin from natural sources and a lack of sequence data, structural studies
of resilin have been limited, although early studies of resilin including elec-
tron microscopy and x-ray diffraction suggest that resilin is an unstructured
amorphous protein matrix, formed by crosslinking of tyrosine residues as
di- and trityrosine complexes (Lyons et al., 2007). The physical properties
of the resilin polymer probably result from the three-dimensional amor-
phous and unstructured nature of the crosslinked protein matrix and the
role of water as plasticizer, because dehydrated crosslinked resilin is very
glassy and brittle, and in a partially dry environment (70% relative humid-
ity) it is leathery with poor resilience. It is possible to store the dehydrated
material for extended periods and then to recover its normal resilience on
rehydration (Elvin et al., 2005).
As for many elastomeric proteins, resilin contains distinct repetitive
domains that appear to confer elastic properties to the protein although
limited sequence homology between species has been reported. The con-
served tetrapeptide YGAP seems to be the critical motif in conferring heat
resistance and hydrophobic properties to resilin and related properties.
Attempts to reproduce the desirable mechanical properties of resilin in
synthetic biomaterials have generated recombinant proteins encoding mul-
tiple copies of consensus polypeptides based on repetitive domains within
resilin-like genes, E. coli being the main host strain employed for over-
expression. It is likely that the resilin-like proteins have a self-associating

propensity, a property that similarly has been identified in elastin. It was
shown that concentrated solutions of all resilin-like recombinant proteins
tested have a tendency to form a concentrated protein lower phase at 4 °C,
whereas the upper phase appears as an opaque solution at this temperature,
suggesting that it has a micellar structure; heating of the cloudy solution

© Woodhead Publishing Limited, 2010