An approach to integrated antibody production: Coupling of fluidized bed cultivation and fluidized bed adsorption

Comparison of histidine-tag capture chemistries for purification following chemical extraction

The purification of a 6x-histidine tagged viral coat protein (L1) in expanded mode directly following chemical extraction from the cytoplasm of Escherichia coli HMS174(DE3) is investigated. Chelating adsorbents based on the ligands iminodiacetic acid (IDA) and nitrilotriacetic acid, using chelated metal ions Ni2+ and Cu2+, were compared. The use of Ni2+-IDA resulted in a high purification factor (9.7) and moderate recovery yield (58%). However, the eluted fractions had an overall L1 purity less than 50% and were therefore significantly contaminated with other host proteins. In batch tests, Cu2+-IDA was found to be superior to all other combinations as it was characterised by higher binding capacities and faster adsorption kinetics. A subsequent immobilised metal affinity chromatography-expanded bed adsorption experiment using Cu2+-IDA resulted in a higher L1 purification factor (20), recovery yield (71%) and purity (89%). The process presented here combines direct chemical extraction with expanded bed recovery. It is simpler than traditional methods, and should find more widespread application in the recovery of inclusion body proteins. Robust pseudo-affinity ligands such as metal chelates show potential for selective primary recovery of unfolded proteins, and could be used for further processing such as on-column refolding.

Direct recovery of glutathione S-transferase by expanded bed adsorption: anion exchange as an alternative to metal affinity fusions

The use of expanded beds of ion-exchange adsorbents for the direct recovery of a recombinant intracellular protein, glutathione S-transferase (GST), from unclarified Escherichia coli homogenates is described. The results form the basis for a comparison between this approach for purifying GST and a chelating fusion strategy and highlight the need to consider the additional costs entailed by these more-complicated approaches. The separation performance was investigated with respect to choice of anion or cation exchanger, adsorption pH, load volume, sample preparation, and stepwise elution protocol. Anion exchange was found to be more appropriate than cation exchange, as the low pHs involved in the latter caused a loss of activity. The optimal pH for adsorption was found to be 9 with a dynamic capacity from clarified homogenate in packed mode of 112 U mL(-1) (11.2 mg GST mL(-1)). As increasing volumes of unclarified homogenate were applied to the expanded bed, the yield of GST in the eluate decreased, and the purification factor was found to increase and then decrease. This was due to the displacement of weakly bound proteins by GST and then its displacement by even more strongly binding proteins. The dynamic capacity of the anion exchanger, STREAMLINE DEAE, from unclarified homogenate in expanded mode decreased slightly to 85 U mL(-1) (8.5 mg GST mL(-1)). The elution protocol for GST from the anion exchanger was then adjusted to try to maximize the degree of purification. Anion exchange expanded bed adsorption of GST from unclarified E. coli homogenate gave an eluted yield of 95.7% and 1.64-fold purification. Interestingly, a decrease in the expression level of GST in the feedstream from 23 down to 13% caused a decrease in the dynamic capacity from 85 to 14.5 U mL(-1) whereas the degree of purification remained similar.

Integrated processing of biotechnology products

Integrated bioprocessing in which a potentially inhibitory product is continuously removed from the fermentation broth as it is produced, has important advantages in improving yield and conversion relative to conventional processes. This review discusses integrated processing for ethanol, butanol, organic acids, antibiotics, and other products. A variety of recovery operations can be used to isolate the product, as discussed. Use of some of the available options is compared.

Facilitated downstream processing of a histidine-tagged protein from unclarified E. coli homogenates using immobilized metal affinity expanded-bed adsorption

The facilitated downstream processing of an intracellular, polyhistidine-tagged protein, glutathione S-transferase [GST-(His)(6)], direct from unclarified E. coli homogenates using expanded beds of STREAMLINE chelating, has been investigated. A series of pilot experiments were used to develop preparative-scale separations of GST-(His)(6), initially in packed and then in expanded beds. Packed beds of Ni(2+)-loaded STREAMLINE chelating proved to have the highest 5% dynamic capacity for GST-(His)(6), of 357 U mL(-1) (36 mg mL(-1)). When using immobilized Cu(2+) or Zn(2+), metal ion transfer was observed from the iminodiacetate ligands to the high-affinity chelator, GST-(His)(6). The subsequent metal affinity precipitation of this homodimer resulted in operational problems. An equilibrium adsorption isotherm demonstrated the high affinity of GST-(His)(6) for immobilized Ni(2+), with a q(m) of 695 U mL(-1) (70 mg mL(-1)) and a K(d) of 0.089 U mL(-1) (0.0089 mg mL(-1)). Ni(2+)-loaded STREAMLINE chelating was therefore selected to purify GST-(His)(6) from unclarified E. coli homogenate, resulting in an eluted yield of 80% and a 3.34-fold purification. The high dynamic capacity in the expanded mode of 357 U mL(-1) (36 mg mL(-1)) demonstrates that this specific interaction was not affected by the presence of E. coli cell debris.

Fluidized bed adsorption as a primary recovery step in protein purification

Fluidized bed adsorption has been introduced as an integrative technology combining clarification, concentration, and initial purification in a single step. In the paper presented here, the use of fluidized adsorbents in the primary recovery of proteins starting from unclarified broths is reviewed. First the principle of fluidizing adsorbent particles is discussed, subsequently possible experimental procedures for whole broth adsorption are demonstrated. The system parameters governing the performance of the sorption process in a fluidized bed are discussed in the second part of the paper and considerations on how operating parameters and process design influence the limiting steps are provided. Finally, examples for the successful operation of whole broth adsorption employing fluidized adsorbents are shown and conditions are defined under which this technology may be an alternative to traditional protein purification methods.

Isolation of monoclonal antibodies from cell containing hybridoma broth using a protein A coated adsorbent in expanded beds

A novel expanded bed adsorbent carrying a recombinant protein A ligand was used for the isolation of monoclonal antibodies from cell containing hybridoma fermentation broth. The untreated effluent from a continuous hybridoma cultivation was applied to the stable expanded adsorbent (Streamline rProteinA), which proved to have a high capacity for the MAb studied (14 mg MAb per ml of adsorbent). A clarified and highly concentrated (up to 50 fold) eluate of high purity was obtained. A scale up of the MAb purification is demonstrated from lab scale (250 mg MAb per purification cycle) to a small pilot scale (2 g MAb per cycle). Low product concentration in the broth in combination with the high capacity of the adsorbent caused long sample application cycles (10-11 h). Experimental problems arising from these long cycle times are discussed with regard to a large scale application of the method.