Biosequestration of carbon dioxide using a silicified carbonic anhydrase catalyst

Abstract

Using recombinant DNA technology, we constructed a dual fusion gene expression plasmid, pRCAH-30, encoding carbonic anhydrase (CA) from the cyanobacterium Synechocystis sp. PCC6803, an R5 peptide sequence, and an affinity (His)₆ tag, to allow the simultaneous purification and immobilization of the encoded fusion enzyme, termed RCAH. The expressed fusion protein was approximately 30 kDa, and could be rapidly purified using affinity resins. To enhance enzyme activity, the R5 peptide facilitated immobilization by means of silicification with tetramethoxysilane; the aggregated particles were approximately 300 nm in diameter. Activity tests revealed that the enzyme functioned optimally between pH 7.0 and 7.5; maximum stability was achieved between 25 and 45°C, at pH 6.0 ∼ 8.0. Activity of the fusion enzyme persisted, even after encapsulation by biomimetic silicification. In fact, silicone embedding stabilized the enzyme structure, thereby increasing its stability and reusability rate under different environmental conditions. In addition, the silicified enzyme reduced waste CO₂ gas from 800 to 42 ppm, resulting in a gas capture rate of 94.7% after conversion. Thus, the construct developed in this study can be effectively utilized for the sequestration of industrial waste CO₂ gas.