(A) Squid skin cells respond with wave of reflected colors when neurotransmitter (ACh) diffuses through tissue (7). (B) In vivo, neurotransmitter (ACh) binds muscarinic receptor, activating G-protein-dependent signal-transduction pathway culminating in enzymatic phosphorylation of reflectins in membrane-bounded lamellae of Bragg reflector (3). Resulting neutralization drives reflectin assembly, osmotic dehydration and photonic changes. (C) In vitro neutralization by mutation or titration triggers proportionally calibrated assembly of reflectin (10, 11). (inset) TEM of reflectin assemblies (10); 50 nm scale.
Reflectin proteins dynamically tune the color and brightness of light reflected from cells in squid skin. Prior Army support enabled us to gain insights into the molecular mechanisms by which reflectins transduce information from signals to continually fine-tune the osmotic pressure of subcellular nanostructures, thus regulating their photonic behavior. Reflectin’s signal-responsive, precisely-calibrated reconfiguration and hierarchical assembly represents a new kind of biomolecular machine—one that transduces information to control colligative properties and thereby tune a range of complex material behaviors (e.g., osmotic-pressure-dependent dimensions of photonic structures). Most recently, we discovered that we can electrically fine-tune reflectin assembly, thus opening a new approach to bridge the biotic-abiotic interface by controlling this and other protein machines. In this project, we propose to build on these findings, using genetic and cellular engineering in conjunction with advanced biophysical, chemical and near-atomic level cryo-TEM analyses to gain a deeper understanding of reflectin’s complex biological mechanism of action. In collaboration with our Army and University partners, we will use this understanding to genetically engineer, enhance and incorporate reflectin into new biotic-abiotic, electrochemical, fabric-based and synthetic biological platforms that harness this new kind of biomolecular machine. With our Army and University partners, we will create new, signal-dependent “reporter” phenotypes in fabrics and in yeast and other synthetic biological constructs, enabling new sensors and other applications.