Red-Shifting B-Dependent Photoreceptor Protein via Optical Coupling for Inducible Living Materials.

Cobalamin (B)-dependent photoreceptors are gaining traction in materials synthetic biology, especially for optically controlling cell-to-cell adhesion in living materials. However, these proteins are mostly responsive to green light, limiting their deep-tissue applications. Here, we present a general strategy for shifting photoresponse of B-dependent photoreceptor CarH from green to red/far-red light via optical coupling. Using thiol-maleimide click chemistry, we labeled cysteine-containing CarH mutants with SulfoCyanine5 (Cy5), a red light-capturing fluorophore. The resulting photoreceptors not only retained the ability to tetramerize in the presence of adenosylcobalamin (AdoB), but also gained sensitivity to red light; labeled tetramers disassembled on red light exposure. Using genetically encoded click chemistry, we assembled the red-shifted proteins into hydrogels that degraded rapidly in response to red light. Furthermore, Saccharomyces cerevisiae cells were genetically engineered to display CarH variants, which, alongside in situ Cy5 labeling, led to living materials that could assemble and disassemble in response to AdoB and red light, respectively. These results illustrate the CarH spectrally tuned by optical coupling as a versatile motif for dynamically controlling cell-to-cell interactions within engineered living materials. Given their prevalence and ecological diversity in nature, this spectral tuning method will expand the use of B-dependent photoreceptors in optogenetics and living materials.