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Synthetic CO2-fixation enzyme cascades immobilized on self-assembled nanostructures that enhance CO2/O2 selectivity of RubisCO

Satagopan, Sriram, Sun, Yuan, Parquette, JonR., Tabita, F.Robert
Biotechnology for biofuels 2017 v.10 no.1 pp. 175
biofuels, carbon, carbon dioxide, carbon dioxide fixation, carboxylation, catalytic activity, engineering, fossil fuels, global warming, glucose, greenhouse gases, immobilized enzymes, industrial effluents, nanomaterials, proteolysis, ribulose 1,5-diphosphate, ribulose-bisphosphate carboxylase
BACKGROUND: With increasing concerns over global warming and depletion of fossil-fuel reserves, it is attractive to develop innovative strategies to assimilate CO₂, a greenhouse gas, into usable organic carbon. Cell-free systems can be designed to operate as catalytic platforms with enzymes that offer exceptional selectivity and efficiency, without the need to support ancillary reactions of metabolic pathways operating in intact cells. Such systems are yet to be exploited for applications involving CO₂ utilization and subsequent conversion to valuable products, including biofuels. The Calvin–Benson–Bassham (CBB) cycle and the enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) play a pivotal role in global CO₂ fixation. RESULTS: We hereby demonstrate the co-assembly of two RubisCO-associated multienzyme cascades with self-assembled synthetic amphiphilic peptide nanostructures. The immobilized enzyme cascades sequentially convert either ribose-5-phosphate (R-5-P) or glucose, a simpler substrate, to ribulose 1,5-bisphosphate (RuBP), the acceptor for incoming CO₂ in the carboxylation reaction catalyzed by RubisCO. Protection from proteolytic degradation was observed in nanostructures associated with the small dimeric form of RubisCO and ancillary enzymes. Furthermore, nanostructures associated with a larger variant of RubisCO resulted in a significant enhancement of the enzyme’s selectivity towards CO₂, without adversely affecting the catalytic activity. CONCLUSIONS: The ability to assemble a cascade of enzymes for CO₂ capture using self-assembling nanostructure scaffolds with functional enhancements show promise for potentially engineering entire pathways (with RubisCO or other CO₂-fixing enzymes) to redirect carbon from industrial effluents into useful bioproducts.