Carboxysome-Inspired Protein Coacervates for Light-Driven CO ₂ Reduction and H ₂ Evolution

Efficient catalysis often requires high local concentrations of reactants and catalysts, which cells achieve through compartmentalization within organelles, such as carboxysomes, that increase the efficiency of bacterial carbon fixation. Here, we engineered a photocatalytic reaction compartment that concentrated an artificial metalloenzyme, carbon dioxide, and a photosensitizer by liquid-liquid phase separation triggered by a cationic polypeptide, deca(L-arginine) (R ₁₀ ). At low R ₁₀ concentrations, CoPPIX binding increases the α-helical structure of the otherwise disordered protein, supercharged cytochrome b ₅₆₂ (–22). At higher concentrations, electrostatic complexation produces spherical droplets that enrich the protein and cobalt cofactor and recruit the photosensitizer [Ru(bpy) ₃ ]²⁺. Under illumination, coacervation increased hydrogen evolution 1.9-fold and CO formation from CO ₂ 1.3-fold relative to the corresponding solution-phase protein system. Co-encapsulation of carbonic anhydrase changed the product distribution specifically in the condensed phase: CO production increased 3.2-fold, H ₂ evolution decreased from 1.51 to 0.70 µmol, and CO selectivity among the detected two-electron products rose from 33% to 77%. These results demonstrate that bioinspired coacervates can stabilize reactive intermediates, enrich local substrate concentrations, and integrate multiple catalytic functions, providing a generalizable framework for programmable, light-driven synthetic organelles.