Red-Shifting B₁₂-Dependent Photoreceptor Protein via Optical Coupling for Inducible Living Materials

Cobalamin (B₁₂)-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 B₁₂-dependent photoreceptor CarH_C from green to red/far-red light via optical coupling. Using thiol-maleimide click chemistry, we labeled cysteine-containing CarH_C mutants with SulfoCyanine5 (Cy5), a red light-capturing fluorophore. The resulting photoreceptors not only retained the ability to tetramerize in the presence of adenosylcobalamin (AdoB₁₂), 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_C variants, which, alongside in situ Cy5 labeling, led to living materials that could assemble and disassemble in response to AdoB₁₂ and red light, respectively. These results illustrate the CarH_C 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 B₁₂-dependent photoreceptors in optogenetics and living materials.