High-level production in a plant system of a thermostable carbonic anhydrase and its immobilization on microcrystalline cellulose beads for CO2 capture.

KEY MESSAGE: Plant-produced SazCA and its application to CO2 capture. Technologies that rely on chemical absorption or physical adsorption have been developed to capture CO2 from industrial flue gases and sequester it at storage sites. Carbonic anhydrases (CAs), metalloenzymes, that catalyze the reversible hydration of CO2 have recently received attention as biocatalysts in the capture of CO2 from flue gases, but their cost presents a major obstacle for use at an industrial scale. This cost, however, can be reduced either by producing a long-lasting enzyme suitable for CO2 capture or by lowering production costs. High-level expression, easy purification, and immobilization of CAs from Sulfurihydrogenibium azorense (SazCA) were investigated in a plant system. Fusion of the 60-amino acid-long ectodomain (M-domain) of the human receptor-type tyrosine-protein phosphatase C increased the levels of SazCA accumulation. Fusion of the cellulose-binding module (CBM3) from Clostridium thermocellum resulted in tight binding of recombinant protein to microcrystalline cellulose beads, enabling easy purification. The chimeric fusion protein, BMC-SazCA, which consisted of SazCA with the M and CBM3 domains, was expressed in tobacco (Nicotiana benthamiana), giving a recombinant protein yield in leaf extracts of 350 mg/kg fresh weight. BMC-SazCA produced in planta was active in the presence of various chemicals used in CO2 capture. Immobilization of BMC-SazCA on the surface of microcrystalline cellulose beads extended its heat stability, allowing its reuse in multiple rounds of the CO2 hydration reaction. These results suggest that production of SazCA in plants has great potential for CA-based CO2 sequestration and mineralization.