Immobilized CmpA: A Novel Approach to Facilitating Bicarbonate Exchange for pH-Mediated Carbon Capture Systems

Abstract

This work presents the first characterization of immobilized CmpA as a means of facilitating bicarbonate exchange within a pH-mediated carbon capture system. The economic and thermodynamic efficiencies of pH-mediated carbon capture systems are closely tied to the ability of their ion exchange mechanisms to selectively transport bicarbonate over other forms of dissolved inorganic carbon (DIC). CmpA is a cyanobacterial membrane-bound bicarbonate binding protein (Kd = 5µM) that has been observed to be highly stable and easily purified. Based on these previous findings, we hypothesized that recombinantly-expressed CmpA immobilized onto a beaded agarose support could be used to transport bicarbonate with high selectivity and for potentially low cost within a carbon capture system. The goal of this project was to recombinantly express and immobilize CmpA, quantify its binding affinity for bicarbonate when free v.s. immobilized, and then measure the ability of immobilized CmpA to transport bicarbonate within a bench-scale carbon capture system. Adapting existing protocols, we were able to express and purify approximately 11 mg of recombinant CmpA, as well as covalent link it to SulfoLinkⓇ immobilization resin. Our attempts to measure the activity of our free and immobilized CmpA, though, showed that our purification products lacked any significant affinity for bicarbonate, yielding Kd= 7.115*1017mM for free CmpA. Furthermore, we did not observe a difference in bicarbonate transport between our CmpA-associated and CmpA-free beaded agarose supports when employed in a bench-scale DAC system. Although inconclusive, the findings of this preliminary examination pave the way for future testing, and outline a number of pitfalls that were encountered.