Many cephalopods (squid, cuttlefish, octopus etc.) exhibit remarkable dermal iridescence (more than meets the eye), a component of their complex, dynamic camouflage and communication. In the species Euprymna scolopes, the light organ iridescence is static and is due to reflectin protein-based platelets assembled into lamellar thin-film reflectors called iridosomes, contained within iridescent cells called iridocytes.
Reflectin hierarchical protein assembly is necessity for the responsive, tunable optical function of iridosome cells. This protein assembly can be triggered by chemical stimulation and that assembly can be reversible and fine-tuned.
Namely reflectin proteins were identified as the major biomaterial component of iridosomes. The RA1 gene in The Rainbow Graveyard Project was artificially synthesized into pBluescript to transform into E. coli. In addition, Kramer et al. (2007) isolated reflectin proteins exhibit unusual solubility and self-association properties.
Self-association of RA1 is likely to stem from a combination of electrostatic and weak aromatic interactions. Reflectins are, indeed, characterized by their high content of polar aromatic residues and arginines, and several lines of evidence suggest that they are intrinsically unstructured, with no likely transmembrane, alphahelix or beta-sheet regions. E. scolopes reflectins also have high arginine, hydrophobic aromatic content and “methionine-rich membrane-associated proteins”. It is demonstrated that they have a high affinity for assembly with microsomal membranes.
The mechanism of reflectance is the same as that of colored soap bubbles. If the soap film (or multilayer plate) is very thin, shorter wavelengths are reflected, e.g. blue light; if it is thicker, longer wavelengths, such as yellow and red, are reflected. The reflectin proteins that apparently change their conformation or assembly to reversibly create the photonic structure.
Multilayer reflector that appears red at near-normal viewing angles will appear first yellow, then green and blue at increasingly oblique angles. This dynamic reflection occurs by altering platelet and inter-platelet thicknesses in the multilayer reflector and/or altering the overall effective refractive index of the intra-platelet material. This allows the entire visible spectrum to be reflected from a single platelet stack. The increase in film thickness resulted in detectable redshift of the visible spectra and dominated any effect of decreasing refractive index owing to water sorption, which would have caused a blue-shift in the spectrum Kramer et al. (2007) have performed Micro-dialysis of reflectin 1a into various buffers, which resulted in two general types of aggregative structures. Optically clear bulk precipitation was seen in non-reducing conditions and filamentous protein structures were observed in reducing conditions controlled through the addition of a 10:1 ratio of reduced to oxidized glutathione .After several weeks at 4 ◦C, the filamentous structures formed a webbed structure that resulted in the supramolecular assembly of thin ribbons.
In our project, we use reflectin 1A for detecting the survival of E.coli. Both of our bacteria (E.coli and B.subtilis) are expected to synthesize reflectin. As LALF is being produced by B.subtilis, both bacteria will synthesize reflectin. Meanwhile, LALF will bind to cell wall of gram negative bacterium (E.coli in our project). Therefore, gram (-) bacteria will not grow and survive in our biofilm surface. During the binding process, production of reflectin layer is going to decrease. Because of this, color of the surface will change due to the light reflecting ability of reflectin depending on the thickness of its layer. So, if the colour changes from red to blue, we can say there was a contact between E.coli and B.subtilis via anti-LPS factor.
- nature materials VOL 6 JULY 2007 (Review.The self-organizing properties of squid reflectin protein, Ryan M. Kramer et al.) Published online: 3 June 2007; doi:10.1038/nmat1930
- J. R. Soc. Interface (2009) 6, S149–S163 doi:10.1098/rsif.2008.0366.focus Published online 15 December 2008 (Review. Structural coloration in cephalopods L. M. Ma¨thger et al. S155)
- Review. Structural coloration in cephalopods L. M. Ma¨thger et al. S161
- DOI: 10.1126/science.1091288 Science 303, 235 (2004); Wendy J. Crookes, et al.(www.sciencemag.org SCIENCE VOL303 9 JANUARY 2004)
- A.R. Tao et al. / Biomaterials 31 (2010) 793–801
- J. R. Soc. Interface (2010) 7, 549–560 doi:10.1098/rsif.2009.0299 Published online 23 September 2009(Reflectin phosphorylation M. Izumi et al.)