Squid Proteins Conduct Protons

Proteins found in the skin of cephalopods may be promising materials for next-generation bioelectronics. Squid, cuttlefish, and their cephalopod kin use proteins known as reflectins to alter their appearance for camouflage. Researchers now report that thin films made of reflectin from the longfin inshore squid, Doryteuthis pealeii, possess proton-conducting properties on par with state-of-the-art artificial proton conductors and could therefore make it possible to use them in protonic transistors (Nat. Chem. 2014, DOI: 10.1038/nchem.1960). “Given the importance of protons for electrical signaling in biology, protonic transistors represent a natural choice for interfacing rugged traditional electronics and biological systems that are decidedly more fragile,” notes the research team, led by Alon A. Gorodetsky of the University of California, Irvine. Gorodetsky and coworkers point out that reflectin has a unique amino acid sequence, which contains a significant number of hydrophilic charged residues as well as a large number of hydrophobic aromatic residues. This sequence, they say, makes reflectin amphiphilic, causing it to aggregate into nanoparticles both in solution and in thin films. The researchers speculate that the films are segregated into distinct hydrophobic regions and proton-conducting hydrophilic water channels—a structure that’s analogous to that of DuPont’s proton-conducting sulfonated fluoropolymer Nafion.