Many cephalopod species employ iridescence both as a means of camouflage and communication. In particular, members of the Loliginid squid family display a mode of tunable iridescence that draws interest as a possible model for biologically inspired dynamically tunable photonic devices. This dynamic tunability is mediated by charge neutralization-induced assembly of the intrinsically unstructured cationic reflectin proteins. Reflectins are found within the lamellae of specialized Bragg reflector cells, where they drive the tuning of color of reflected light across the visible spectrum. To understand the mechanisms controlling the tunable assembly of the reflectins, we studied assembly of wild type and mutant recombinant Doryteuthis opalescens reflectin A1 as a function of pH using dynamic light scattering (DLS) and native tryptophan fluorescence. Additionally, we have begun investigations into liquid-liquid phase separation as an avenue to reflectin assembly in vivo. To more deeply understand the mechanism governing tunable assembly, we used cryo-TEM and bright field microscopy to visualize reflectin assemblies under near-physiological conditions. Our experiments revealed the underlying mechanistic relationships between neutralization of protein net charge density, screening of electrostatic interactions and reflectin assembly. These findings highlight the role of electrostatic neutralization as a driver of the emergence of secondary structure and subsequent hierarchical assembly in the tunable reflectins, and help further elucidate a possible mechanism for the creation of biologically inspired photonic devices.

Drivers of tunable iridescence in squid skin

255th National Meeting (2018)

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