Size-exclusion simulated moving bed chromatographic protein refolding

Abstract

Size-exclusion chromatographic refolding (SECR) has successfully proven its capability to refold a variety of proteins using a range of gel filtration column materials. Several approaches have also been undertaken to improve the refolding yield of these systems, mostly under batch operation. Although, these approaches may lead to an increase on refolding yield, it is not expected that they will lead to significant increases in other important process indicators, such as volumetric productivity, specific eluent consumption and product concentration in the product stream; as these indicators are strongly dependent on the mode of operation. To overcome the shortcomings of batch chromatography, the size-exclusion refolding reactor may be operated in a continuous mode, with the aid of Simulated Moving Bed (SMB) technology. Albeit, SMB technology has inherent advantages over batch chromatography, these have been proven mainly in the context of conventional purifications and are still to be addressed in the context of chromatographic refolding reactors. In this work we report the on-column refolding of an industrially relevant protein, produced in inclusion bodies, by batch size-exclusion chromatography (SEC) and simulated moving bed size-exclusion chromatography (SMBSEC). The presented study encompasses: (1) a statistical design of experiments (DOE) to study the combined effect of the mobile phase pH (9.0–11.20) and the feed concentration of denatured and reduced protein ( C f, D& R =2.50–7.50 mg ml −1) on the refolding yield of the model protein; (2) a mechanistic analysis of the SMBSECR data, using a detailed model that accounts for both separation and refolding; and (3) a detailed comparison of the SMBSECR against the SECR, based both on quantitative and qualitative criteria. Our work showed that: (1) refolding yields of 50% are attainable by tuning pH and C f, D& R , and that the positive effect of pH is strongly dependent on the C f, D& R ; (2) the modeling tool captured well the SMBSECR behavior, based solely on the effect that C f, D& R has on the reaction rates; and (3) the volumetric productivity of the SMBSECR is about 53 times higher than that of the SECR, the specific solvent consumption is approximately 1/10th of that of the SECR, and the concentration of the product (i.e., native protein), leaving the SMBSECR, is roughly 4.5-fold higher than the one leaving the SECR. Accordingly, the comparison revealed the significant advantages that SMB technology has to offer to the design of chromatographic refolding reactors.