Image: http://www.murg.esm.vt.edu/research/images/L_murg-research-MPR-8.jpg
The protein structure of resilin. Close examination reveals a lack of alpha helices
and beta sheets that might be found in other elastomeric proteins.
Introduction to Resilin
0 Elastomeric protein found in the elastic tendons and
wing-hinges of many insects.
0 First discovered by Torkel Weis-Fogh in locust winghinge, paper published 1960.1
0 Within a year, resilin was discovered in the salivary
pump of assassin bugs2 and in the feeding pump of
Rhodnius prolixus3. It has been found in the wingfolding mechanism of Dermaptera earwigs recently.4
0 Seems to be nature’s protein version of a spring.
This picture shows the location
of the fluorescent resilin pad in
the legs of the flea.
The fluorescence is due to the
dityrosine residues in the
resilin protein.
Image:
http://www.voyle.net/Images%202005/Oct%202005/17
-10-2005-001.jpg
Fleas are known to be able to
jump over 150 times the length
of their body, and resilin plays a
key role in their jumping, as it
is compressed and then
releases the energy extremely
efficiently to allow the flea to
jump. The energy stored up
from the leg muscles’
compression is released from
resilin within 1 millisecond.
Commercial Importance of Resilin
0 Most efficient elastomeric protein known to man
currently, with a 97% efficiency in conversion of
energy.
0 Natural resilin must last for the lifetime of insect,
hence it must be able to be deformed and reformed
millions of times without severe degradation.
0 Hence a possible substitute for rubber that is even
superior to rubber and easier to produce.
0 Unmatched mechanical abilities: it demonstrated
perfect elasticity even after being strained for twice
its original length for two weeks, and had no tearing
nor fatigue when stressed within its natural limits.1
Resilin’s Properties
0 Unaffected by deep freezing nor heating until 125°C,
which is unusual for a protein.
0 Unaffected by alcohols and fixatives such as formalin
or Bouin’s Solution (used for embryonic studies).
0 Energy loss at 200Hz under 5%5, compared to the
previous best elastic material polybutadiene, which
had an efficiency of 80%.
0 Unfortunately, resilin is degraded by proteolytic
enzymes, hence artificial resilin will have to address
this issue.
Structure of Resilin
0 620 amino acids long, including a signal peptide of 17
residues at the N-terminus, suggesting that the
protein is secreted into the extracellular space.
0 It has a relative molecular mass of 56771 daltons and
a calculated isoelectric point of 5.0.
0 Composed of 3 domains: a central 62-residue domain,
324 residue long N-terminal region and a 217 residue
long C-terminal.
0 Believed to exhibit elasticity because of immense
cross-links composed of dityrosine and trityrosine,
which also give it fluorescent properties.6
Autofluoresence
under UV light from
resilin present in male
genitalia of a giant
water bug, Belostoma
lutarium.
Image: http://jeb.biologists.org/content/210/22/3879/F3.large.jpg
Molecular Basis for Resilin Elasticity
0 Resilin has a repeated 15-residue motif (with 18 slight
variants) in the N-terminal region that is rich in
glycine with 2 prolines and a tyrosine,
GGRPSDSYGAPGGGN.
0 The C-terminal region possesses a 13-residue motif
(with 11 slight variants) of glycine, tyrosine but only 1
proline, GYSGGRPGGQDLG.
0 These tyrosines are then used to form dityrosines and
trityrosines which cross-link between peptide chains.
Molecular Basis for Resilin Elasticity
0 Weis-Fogh was able to determine that elasticity of resilin
was affected by the hydration and the pH of the protein.1
0 It has been suggested that another component of the
elasticity comes from the hydration of the peptide chains.
0 Peptide groups will more easily hydrogen-bond to water
than each other, causing a slightly irregular chain-folding
that prevents cooperativity in inter-chain bonds, allowing
limited links in the form of dityrosine and trityrosine links.
0 This creates a protein that has cross-links in 3D, rendering
it highly compressible and efficient in energy transmission.
Artificial Resilin
0 In a paper published in 2005, a group of Australian
scientists led by Dr Chris Elvin of the Commonwealth
Scientific and Industrial Research Organisation (CSIRO)
successfully synthesised resilin through genetic
engineering.
0 The synthetic resilin was produced through isolation of the
resilin gene from D. melanogaster and inserted into E. coli,
which produced the precursor pro-resilin.
0 Pro-resilin was then mixed with ruthenium catalyst under
a light which created tyrosine cross-links. Within 20
seconds, the texture changed into a rubbery solid with
properties identical to natural resilin.7
Image: http://jeb.biologists.org/content/210/22/3879/F3.large.jpg
Bio-synthesised resilin moulded into a flexible rod by drawing pro-resilin into a glass
tube, followed by photochemical cross-linking of the precursor. Left, the rod illuminated
by white light. Right, the same rod illuminated by U.V. light at 315 nm showing its
fluorescence at 409 nm.
Lucky Guess?
0 By studying other elastomeric proteins such as
elastin, the CSIRO group reasoned that resilin was
likely to have highly-repetitive sequences.
0 As such, the genes that coded for resilin was also
likely to have highly-repetitive sequences.
0 Given that the gene that produced resilin was already
identified, the researchers picked out a small section
of DNA that contained large amounts of repeating
elements in the hope that it would produce resilin.
Insights into Resilin from Artificial Resilin
0 Closer study of the synthetic resilin eventually provided
much information on the nature of resilin.
0 Secondary structure studies led by CSIRO scientists
examined a 16-unit consensus sequence repeat, known as
AN16.8
0 It was discovered to be structurally similar to many
denatured proteins and intrinsically unstructured. Alphahelical and beta-sheets were not observed in the NMR
spectroscopy.
0 Evidence was discovered through the NMR spectra that the
Tyr-Gly-Ala-Pro sequence showed lower dependence on
hydration, implying that the residues were involved in
hydrogen-bond formation.
Insights into Resilin from Artificial Resilin
0 The group concluded that the most likely model for
resilin’s elasticity was a mix of random-network
elastomers and sliding beta-turns.
0 This was further confirmed by a subsequent study
which synthesised novel recombinant proteins with
repetitive domains based off resilin genes in D.
melanogaster and A. gambiae.9
0 The recombinant proteins produced were extremely
similar to natural resilin in terms of modulus,
elasticity, resilience and dityrosine content.
Conclusion
0 While much headway has been made to understand the
unique structural properties that give resilin such an
unparalleled position in terms of elasticity and resilience,
much work needs to be done to synthesise artificial resilin
usable.
0 Potential applications include in spinal disc implants, heart
and blood valve substitutes and high efficiency industrial
rubbers. They could also be deployed in nanosprings and
microactuators.
0 The major hurdle to overcome however, is its denaturation
by proteases, as well as the effect of pH and hydration on
its mechanical properties.
References (I)
1 Weis-Fogh,
T. (1960). A rubber-like protein in insect cuticle. J. Exp. Biol.
37,889 -907.
2 Edwards, J. S. (1960). Predation and digestion in assassin bugs
(Heteroptera, Reduviidae). PhD thesis, University of Cambridge, UK.
3 Bennet-Clark, H. C. (1963). Negative pressures produced in the
pharyngeal pump of the bloodsucking bug, Rhodnius prolixus. J. Exp. Biol.
40,223 -229.
4 Haas, F., Gorb, S. and Wootton, R. J. (2000). Elastic joints in
dermapteran hind wings: materials and wing folding. Arthropod Struct.
Develop. 29,137 -146.
5 Jensen, M. and Weis-Fogh, T. (1962). Biology and physics of locust flight.
V. Strength and elasticity of locust cuticle. Phil. Trans. Roy. Soc. Lond. B
245,137 -169.
References (II)
O. (1964). The cross links in resilin identified as
dityrosine and trityrosine. Biochim. Biophys. Acta 93,213 -215.
0 7 Elvin, C. M. et al (2005) Synthesis and properties of crosslinked
recombinant pro-resilin. Nature, Oct 13 2005. Vol 437, No. 7061, pp.
999-1002
0 8 Nairn, K. M. et al (2008) A synthetic resilin is largely unstructured.
Biophys J. 2008 Oct ;95(7):3358-65. Epub 2008 Jun 27.
0 9 Lyons, R. E. et al (2009) Comparisons of recombinant resilin-like
proteins: repetitive domains are sufficient to confer resilin-like
properties. Biomacromolecules. 2009 Nov 9;10(11):3009-14.
0
6 Andersen, S.