Melt stability of carbonic anhydrase in polyethylene oxide for extrusion of protein–polymer composite materials

Abstract

Carbonic anhydrase is an enzyme which can convert dissolved carbon dioxide into carbonate and is commonly investigated in carbon capture applications as a green alternative to sequester carbon. It is common to immobilize the enzyme within a scaffold or polymer matrix for these applications to improve the efficiency and lifetime of the enzyme. A potential manufacturing route to generate protein–polymer composite materials at scale is melt processing: a technique capable of processing large amounts of material into pre-defined geometries. Intuitively, for such applications, the carbonic anhydrase would need to retain its activity under the harsh temperature and shear conditions associated with polymer melt processing, which had yet to be demonstrated. This manuscript demonstrates the recovery of active bovine carbonic anhydrase following high temperature and low- to moderate-shear exposure in a polyethylene oxide melt using both rheometry and twin-screw extrusion. Following processing, kinetic assays demonstrate that the enzyme can retain measurable amounts of activity, even following treatment up to 190 °C. Activity assays are supported by spectroscopic measurements suggesting that no significant structural change in the enzyme occurs until roughly 160 °C. Retaining more protein activity at higher temperatures appears to be related to the molecular weight of the polyethylene oxide in the melt. In sum, we demonstrate that carbonic anhydrase can retain appreciable activity following the rigors of melt processing in model systems and under real-world twin-screw extrusion.