Novel Self-Cleaving Affinity Purification Method for Cellular Membrane-Associated Recombinant Paraoxonase-1 (rePON1) Enzyme

Mammalian paraoxonase-1 (PON1) is a ~ 39.45 kDa calcium-dependent hydrolytic enzyme with potential therapeutic applications in chemical defense and cardiovascular disease. The N-terminus of PON1 is embedded in the cellular membrane, imparting to a hydrophobic character that leads to increased aggregation propensity and instability during purification. Although some advances have been made in bacterial expression hosts by using solubility-enhancing fusion tags and detergent solubilization strategies, these studies have shown that proteolytic tag removal is generally problematic. Thus, ineffective tag removal limits the bioanalytical characterization of the enzyme. Furthermore, the need for stabilizing detergents during purification limits the options for affinity-tag based methods. In this study, we demonstrate a novel affinity purification strategy by combining two solubility-enhancing fusion partners with the iCapTag™ self-removing affinity tag, where the entire purification process takes place in the presence of detergent. Optimization of purification conditions, including detergent and pH, resulted in the successful solubilization and stabilization of rePON1 at room temperature, allowing the tagless and native protein to be characterized. The results confirmed the expected catalytic efficiency and molecular weight of the enzyme. This method achieved over 95% host-cell protein impurities and more than 99.9% clearance of the host cell's double-stranded DNA in a single-column affinity operation. This approach combines the power of affinity chromatography and facile tag removal, thereby offering a versatile and efficient alternative to produce other recombinant membrane-associated proteins, as well as additional target proteins that require challenging buffer conditions.