Proteinaceous optical devices in squids: understanding the reflectin-lipid interaction

The self-assembly of reflectins, a family of proteins in cephalopods, gives rise to optical properties like iridescence. The resulting structure consists of thin layers of reflectins sandwiched between the cell membrane; the high refractive index contrast between assembled reflectin and the extracellular fluid allows strong interaction with light. Simulations suggest that reflectins are partially unfolded and form a potentially novel interaction with the lipid bilayer resulting in the interdigitation of the lipid tails between membrane leaflets. This interaction is correlated with a shift in the physicochemical properties of the membrane. SANS results show that reflectin-lipid interactions cause changes in the larger assembled structure at length scales much greater than that of a single protein. SAXS data suggest that lamellar membrane structures that disappear with increasing experimental temperature are present. The temperature above which the lamellae disappear is higher when reflectin is present in the system. Our data suggest that reflectins trigger structural changes in lipid bilayers that in turn influence the material properties and resulting geometric configurations of the plasma membrane in living cells.