From the renaturation kinetics of denatured/reduced lysozyme assisted by the molecular chaperone GroEL, a simplified kinetic model was established based on the competition between protein folding and aggregation. In the presence of GroEL and ATP, the aggregate formation was a second order reaction. With 2mM ATP, a renaturation yield of 90% at a high renaturation rate was obtained when the molar ratio of GroEL to lysozyme was 1: 1.

Interest in producing large quantities of plasmid DNA has recently increased as a result of the rapid evolution of gene therapy and DNA vaccines. Hydrophobic chromatography is a popular technique in the downstream processing of plasmid DNA. However, the low capacity and the high mass transfer resistance of most commercially available packings for bio-macromolecules limit their application in a large-scale process. In this work, a hydrophobic absorbent with wide pores was synthesized by the solid porogenic method. Analyses by scanning electron microscopy and mercury intrusion porosimetry revealed that the matrix contained two families of pores, i.e., micropores smaller than 100 nm and superpores of 500-7300 nm. The superpores provided not only convective flow channels for the mobile phase, but also a large surface for biomolecules binding. So the chromatographic process can be operated at high flow rate with high column efficiency and low backpressure as identified on a 2-mL column (5mm i.d., 2cm length). With a loading up to 2.6 mg of 5.4 kb plasmid (pcDNA3) in 8mL feedstock and operated at a flow rate as high as 20 cm/min, nearly 100% of plasmid was recovered with a purity of 100%. The results indicate that the hydrophobic medium is promising for high-speed purification of plasmid DNA.

Sorbitan trioleate was modified with Cibacron Blue F-3GA (CB) to create an affinity surfactant and to form affinity-based reverse micelles in nhexane. The partitioning equilibria and the extraction kinetics of lysozyme and bovine serum albumin (BSA) were then examined. The solubilization capacity of the reverse micellar system for lysozyme increased linearly with increasing the CB concentration from 0.1 to 0.5 mmol L−1. In contrast, the capacity for BSA at 0.5 mmol L-1 of coupled CB was only about one-fifth that for lysozyme. It indicates a strong steric hindrance effect of the micelles for the high molecular mass protein. The overall volumetric mass transfer coefficient of lysozyme in the forward extraction increased from 0.43×10−3 to 1.25×10−3 s−1 with increasing CB concentration from 0.1 to 0.5 mmol L−1. Due to the high molecular mass of BSA, its volumetric mass transfer coefficient in the forward extraction was only one-sixth that of lysozyme. The ratio of the coefficient in the back extraction to that in the forward extraction was less than 0.03, much lower than those in other micellar systems. It indicates that the interfacial resistance in this system was severer than in others.

Sorbitan trioleate (Span 85) modified with Cibacron Blue F-3GA (CB) was used as an affinity surfactant (CB-Span 85) to form affinity-based reversed micelles in n-hexane. It was found that the addition of hexanol to the reversed micellar system resulted in a significant increase in water content and hydrodynamic radius of the affinity-based reversed micelles. Moreover, the reversed micelles with hexanol revealed broader aggregation number distribution and larger average aggregation number than the reversed micelles without hexanol addition. This is considered to be due to the decreases in the micellar curvature and rigidity of the micellar interfacial layer and the increase in the micellar interfacial fluidity. Consequently, the solubilization capacity of lysozyme increased about 70% in the reversed micellar solution with 3 vol% hexanol. On the other hand, the capacity of BSA was only 30% increased under the same conditions due to its larger molecular size than lysozyme. Kinetic analysis revealed that the increase in the micellar interfacial fluidity in the presence of hexanol resulted in faster release of lysozyme from the micelles, thus leading to an increase of the overall volumetric mass transfer coefficient in the back extraction.

It has been recognized that the artificial chaperone system, cetyltrimethylammonium bromide and β-cyclodextrin, is effective for enhancing protein renaturation. In this work, we studied the effect of the artificial chaperone system and guanidinium chloride (GdmCl) on the oxidative renaturation of lysozyme at 0.21-1.05mg/mL, and a kineticmodel based on the competition between protein folding and aggregation was employed to express the renaturation process. The refolding rate constant increased, while the aggregation rate constant decreased, with increasing concentration of the artificial chaperones. With increasing GdmCl concentration (0.28-2M), both rate constants decreased, but there existed a specific GdmCl concentration that maximized the ratio of the two rate constants and thus the renaturation yield. The results obviously indicated the cooperative effect of GdmCl and the artificial chaperones on enhancing protein renaturation.