Interactions between proteins and cation exchange adsorbents analyzed by NMR and hydrogen/deuterium exchange technique / 生物工程学报

In silico acquirement of the accurate residue details of protein on chromatographic media is a bottleneck in protein chromatography separation and purification. Here we developed a novel approach by coupling with H/D exchange and nuclear magnetic resonance to observe hen egg white lysozyme (HEWL) unfolding behavior adsorbed on cation exchange media (SP Sepharose FF). Analysis of 1D 1H-NMR shows that protein unfolding accelerated H/D exchange rate, leading to more loss of signal of amide hydrogen owing to exposure of residues and the more unfolding of protein. Analysis of two-dimensional hydrogen-hydrogen total correlation spectroscopy shows that lysozyme lost more signals and experienced great unfolding during its adsorption on media surface. However, for several distinct fragments, the protection degrees varied, the adsorbed lysozyme lost more signal intensity and was less protected at disorder structures (coil, bend, and turn), but was comparatively more protected against exchange at secondary structure domains (α-helix, β-sheet). Finally, the binding site was determined by electrostatic calculations using computer simulation methods in conjunction with hydrogen deuterium labeled protein and NMR. This study would help deeply understand the microscopic mechanism of protein chromatography and guide the purposely design of chromatographic process and media. Moreover, it also provide an effective tool to study the protein and biomaterials interaction in other applications.

Purification of recombinant human antithrombin III expressed in a goat mammary bioreactor / 生物工程学报

Antithrombin III (AT III) is the most important anti-clotting substance. Recombinant human antithrombin III (rhAT III) expressed in transgenic goat milk attracts more and more attention. Develop an effective purification route for rhAT III is vital to its industrial production. An efficient purification method was developed for the rapid purification of rhAT III by isoelectric precipitation and heparin affinity chromatography. First, casein was effectively removed by isoelectric precipitation. rhAT III was further purified by heparin affinity chromatography. In the process of heparin affinity chromatography, the effects of pH and temperature on the stability of rhAT III were studied, and the effects of operating conditions, elution gradient, flow rate and sample loaded, on the purification efficiency were also studied. Under the optimized conditions, the protein recovery of rhAT III was about 90% with purity over 99%, while its activity recovery was about 50%. Such a purification process is very simple and effective, and it would provide a valuable reference for the further scaling-up of industrial production.

Effect of affinity medium and solution conditions on endotoxin removal from protein solutions / 生物工程学报

Endotoxin removal is essential for the safety of biological products. To remove endotoxin efficiently, we used polymyxin B (PMB) affinity adsorbent to remove endotoxin from protein solutions by static adsorption. We studied the effects of spacer length and ligand density of the affinity adsorbent, pH, salt type and concentration, protein type and concentration, endotoxin concentration, and additive on endotoxin removal and protein recovery. Endotoxin content and protein concentration were determined by test and Lowry assay respectively. The results showed that PMB affinity adsorbent had high capacity, high adsorption speed, high removal efficiency and good reusability. In addition, ligand density, pH, salt concentration and the isoelectric point and hydrophobicity of protein all had remarkable influence on the endotoxin removal. Under the optimal conditions, the recoveries of hemoglobin, human serum albumin and lysozyme were 87.2%, 73.4% and 97.3%, respectively, and the corresponding endotoxin removal rates 99.8%, 97.9% and 99.7%, respectively. This study illustrated the effects of solution conditions on the efficiency of endotoxin removal and protein recovery, and would provide useful reference for the efficient removal of endotoxin from biological products.

Effects of solvent environment on the structure of hepatitis B surface antigen (HBsAg) / 生物工程学报

As a virus-like particle, hepatitis B surface antigen (HBsAg) was the primary component of hepatitis B vaccine. HBsAg was maintained by the non-covalent interaction of proteins and lipids. The intact structure of HBsAg particle was vital to its function. However, there was no report about the effects of solvent environment on HBsAg structure. In this paper, we studied the effects of temperature, pH, ionic type and salt concentration on HBsAg structure. The results showed that HBsAg was stable at normal temperature, but began to denature above 60 degrees C. The aggregation of HBsAg at pH 3.0 and 4.0 was nearly irreversible, but partly reversible at pH 5.0. The influence of ionic type on HBsAg was generally in accordance with Hofmeister sequence, except that SO4(2-) caused more aggregation than F-. HBsAg aggregates started to be visible in 0.4 mol/L (NH4)2SO4, and the extent of aggregation increased with the salt concentration. Therefore, caution must be taken when using (NH4)2SO4 in the hydrophobic chromatography purification of HBsAg.

Preparation of aminated porous resin and for bilirubin adsorption / 生物工程学报

Polystyrene microspheres (PS) were successfully prepared by suspension polymerization processes. Chloroacetylated polystyrene has been prepared by Friedel-Crafts acetylation of PS with chloroacetyl chloride. In this report, carcinogenic compound (chloromethylether etc.) was avoided. The effects of solvent, catalyst, acylating agent and reaction time were studied. Novel adsorption resins were obtained by synthesis of chloroacetylated polystyrene with amine. The influences of solvent, amine reagent and reaction time on ion exchange capacity were investigated. Under the optimized reaction condition, the ion exchange capacity of the prepared resins was 4.1587 mmol/g. The maximum amount of adsorbed bilirubin was 30.85 mg/g, the adsorption percentage was 80%.

Interferon alpha-2b modified with polyethylene glycol / 生物工程学报

In order to obtain a more stable PEGylated interferon alpha-2b, and prolong its half life, interferon alpha-2b (IFN alpha-2b) was modified with monomethoxy polyethylene glycol propionaldehyde (mPEG-ALD) 20000. It was found that the optimized reaction condition for the maximum bioactivity and highest PEGylation degree of the mono PEGylated interferon alpha-2b was as follows: in 20 mmol/L, pH 6.5, citric acid and sodium dihydrogen phosphate buffer, the concentration of IFN alpha-2b was 4 mg/mL, and the molar ratio of PEG/IFN alpha-2b was 8:1, and the reaction time was 20 h at 4 degrees C. Under the optimized reaction condition, the mono PEGylation degree reached to 55%. Ion exchange chromatography was used to separate and purify mono PEGylated interferon alpha-2b from the reaction mixture. The purity of mono PEGylated interferon alpha-2b was higher than 97% characterized by HPLC. The bioactivity of the mono PEGylated interferon alpha-2b was 13.4% of the native IFN alpha-2b, while its half life in SD rat is much longer than the native IFN alpha-2b. The mono PEGylated interferon alpha-2b is also stable in aqueous.