Inert enzyme nanoaggregates for simultaneous biodecarboxylation and CO₂ conversion

Reducing carbon dioxide (CO₂) emissions from bioprocesses has received increasing attention. Coordination complex between metal ion and ligand is the most promising way to prepare self-assembled enzyme nanoaggregates. Co²⁺ ions can rapidly self–assemble with His₆–tag enzymes through metal ion coordination to form nanoaggregates. However, the Co²⁺–enzyme nanoaggregate is kinetically labile and thus undergoes rapid, dynamic dissociation. We therefore used hydrogen peroxide to oxidize the labile Co²⁺–enzyme nanoaggregate into the inert Co³⁺–enzyme nanoaggregate. Inert Co³⁺ almost completely precipitates His₆–tagged lysine decarboxylase (CadA). The Co³⁺–CadA nanoaggregate has excellent catalytic activity and high-affinity binding as well as being resistant to chelators, denaturants, and organic solvents. More importantly, the Co³⁺–CadA/CA (carbonic anhydrase) nanoaggregate significantly reduces CO₂ emissions from biodecarboxylation: its CO₂ conversion efficiency increased by 40.7%, compared with no CA. Our study demonstrates that inert enzyme nanoaggregates can convert simultaneously the released CO₂ from biodecarboxylation efficiently and have a broad application prospect.