CPOS Seminar: Reversible and size-controlled assembly of reflectin proteins using a charged azobenzene photoswitch

Speaker: Cassidy Tobin, Ph.D. Candidate, Department of Chemical Engineering, Read de Alaniz Group, UCSanta Barbara 

Abstract: Disordered proteins often undergo a stimuli-responsive, disorder-to-order transition which facilitates dynamic processes that modulate the physiological activities and material properties of cells, such as strength, chemical composition, and reflectance. It remains challenging to gain rapid and spatiotemporal control over such disorder-to-order transitions, which limits the incorporation of these proteins into novel materials. The reflectin protein is a cationic, disordered protein whose assembly is responsible for dynamic color camouflage in cephalopods, and it would be advantageous to control this behavior within a synthetic material. In this talk, a novel, multivalent azobenzene photoswitch is shown to be an effective and non-invasive strategy for reversibly triggering the co-assembly and disassembly of reflectin molecules and thereby controlling assembly size. Such co-assembly behavior exploits the multivalent architecture of the azobenzene molecules which have multiple anionic moieties that interact with and neutralize the cationic moieties of reflectin. Photoisomerization between the trans and cis photoisomers promotes or reduces Coulombic interactions, respectively, with reflectin proteins to repeatedly cycle the sizes of the photoswitch-reflectin assemblies between 70 nm and 40 nm. The protein assemblies formed with the trans and cis isomers show differences in interaction stoichiometry and secondary structure, which indicate that photoisomerization modulates the photoswitch-protein interactions to change assembly size. Our results highlight the utility of photoswitchable interactions to control reflectin assembly and provide a tunable synthetic platform that can be adapted to the structure, assembly, and function of other disordered proteins.