Team:Cambridge/Project

Project Details

Reflectin and its Properties - A summary of our literature review

In choosing our project we read all the papers we could find on reflectin and several on the squid species that have been studied.

What species of squid have reflectin proteins?

Reflectin was first identified in the Hawaiian bobtail Euprymna scolopes as the protein responsible for this species' iridescence. Reflectin 1a from E. scolopes has been successfully expressed in E.coli and purified ^[1]. Related proteins in Lolliguncula brevis and in squid of the genus Loligo have attracted much research interest due to their ability to actively control their iridescence, a property termed dynamic iridescence.

What purpose do reflectins have in these species? - Iridophores

Reflectins are contained within stacks of repeating membranous structures known as iridophores within cells in squid skin. Within these structures, the reflectin proteins self-assemble to form a natural 'Bragg reflector'^[3]. Along with other cell types with optical properties these Bragg stacks contribute to the squid's ability to camouflage itself and communicate with other animals via manipulation of incident light.

What is a Bragg reflector? - Thin film Interference

Bragg reflectors are structures of alternating layers of materials with different refractive indices. These structures dominantly reflect at a certain peak wavelength in relation to the individual separation of the layers. Each boundary layer exhibits partial reflection which through superposition lead to interference phenomena. The peak reflected wavelength is 4 times the spacing distance between layers whereby the path difference is such as to allow constructive interference. This is the fundamental principle behind thin film interference, responsible for the rainbow colours reflected by oil droplets on the surface of water and that present on soap films.

What is dynamic iridescence and how does it work in squid? - Phosphorylation

Iridescence describes the material colour change as the viewing angle or the angle of incidence of light is varied. However dynamic iridescence, observed in certain squid genera is believed to be a result of neural control. Specifically, the application of the neurotransmitter Acetyl Choline (ACH) to fresh skin samples resulted in detectable post-translational modifications of the protein, namely phosphorylation. It is believed that phosphorylation of reflectin proteins cause changes in the chemical interactions within the nanoparticles reflectin forms in-vivo within the iridophore. These changes subsequently induce an alteration in the volume of protein platelets of reflectin and critically the thicknesses of reflectin layers in the iridophore. The path difference between incident light on individual layers is thus altered resulting in a shift in peak reflected wavelength and therefore colour.

What is known about the nucleotide sequence of reflectins?

No introns were found in the reflectin genes when reflectin genes amplified from Euprymna scolopes genomic DNA were sequenced^[2].

What is known about the unusual amino acid content of reflectins?

What is known about the structure of the reflectin proteins?

What are the differences and conserved sequences between different reflectins and between reflectins in different species?

What work has been done on expressing reflectins in E.coli?

What in vitro experiments have been performed on reflectins?

What are the properties of in vitro films of reflectin?

The Experiments

Part 3

Results

References

[1] Kramer et al. The self-organizing properties of squid reflectin protein Nature Materials 533-538 VOL6 JULY 2007

[2] Crookes et al. Reflectins: The Unusual Proteins of Squid Reflective Tissues SCIENCE 235-238 VOL303 9 JANUARY 2004

[3] Morse et al. The role of protein assembly in dynamically tunable bio-optical tissues Biomaterials 793-801 VOL31 FEBRUARY 2010