Bioinspired Silica Nanocomposite with Autoencapsulated Carbonic Anhydrase as a Robust Biocatalyst for CO2 Sequestration

Here, we report on the development and characterization of a carbonic anhydrase (CA)-based biocatalyst encapsulated in a biosilica matrix for use in environmental CO2 sequestration. Encapsulation occurred simultaneously with autonomous silica synthesis by silica-condensing R5 peptide that was fused to recombinant CA. The encapsulation efficiency was greater than 95%, and the encapsulated CA was not leached from the silica matrix, demonstrating the highly efficient RS-mediated autoencapsulation process. The catalytic efficiencies for both esterase and CO2 hydratase activities tended to increase with increasing pH; however, the catalytic efficiency for CO2 hydration was much more pH dependent, suggesting that proton transfer from silica to water is a rate limiting step, especially for CO2 hydration. In addition to good reusability, the encapsulated CA exhibited outstanding thermostability, even retaining 80% activity after 5 days at 50 degrees C. The thermoactivity was also remarkable, showing similar to 10-fold higher activity at 60 degrees C compared to that at 25 degrees C. The physical structure was observed to be highly compact with a low surface area, stressing the importance of the outermost surface for catalytic performance. We also demonstrated the applicability of the silica nanoparticle to the sequestration of CO2 in carbonate minerals. The rate of CaCO3 precipitation was remarkably accelerated by the encapsulated biocatalyst. The biosilica nanocomposite exhibited similar to 60% of the CO2 sequestrating power of the free enzyme, which is expected to be the maximal ability of the encapsulated CA. Thus, this silica-CA nanocomposite, efficiently synthesized via a biomimetic green route, can be successfully used as a robust biocatalyst for biomimetic sequestration of the greenhouse gas CO2.