Engineering a recyclable elastin-like polypeptide capturing scaffold for non-chromatographic protein purification

Synthesis of single-chain antibody fragment fused to the elastin-like polypeptide in Nicotiana benthamiana and its application in affinity precipitation of difficult to produce proteins

Plants are economical and sustainable factories for the production of recombinant proteins. Currently, numerous proteins produced using different plant-based systems with applications as cosmetic and tissue culture ingredients, research and diagnostic reagents, and industrial enzymes are marketed worldwide. In this study, we aimed to demonstrate the usefulness of a plant-based system to synthesize a single-chain antibody (scFv)-elastin-like polypeptide (ELP) fusion to be applied as an affinity precipitation reagent of the difficult to produce recombinant proteins. We used the human tissue transglutaminase (TG2), the main celiac disease autoantigen, as a proof of concept. We cloned a TG2-specific scFv and fused it to a short hydrophobic ELP tag. The anti-TG2-scFv-ELP was produced in Nicotiana benthamiana and was efficiently recovered by an inverse transition cycling procedure improved by coaggregation with bacteria-made free ELP. Finally, the scFv-ELP was used to purify both plant-synthesized human TG2 and also Caco-2-TG2. In conclusion, this study showed for the first time the usefulness of a plant-based expression system to produce an antibody-ELP fusion designed for the purification of low-yield proteins.

Purification of Therapeutic Antibodies Using the Ca2+-Dependent Phase-Transition Properties of Calsequestrin

Affinity chromatography utilizing specific interactions between therapeutic proteins and bead-immobilized capturing agents is a standard method for protein purification, but its scalability is limited by long purification times, activity loss by the capturing molecules and/or purified protein, and high costs. Here, we report a platform for purifying therapeutic antibodies via affinity precipitation using the endogenous calcium ion-binding protein, calsequestrin (CSQ), which undergoes a calcium ion-dependent phase transition. In this method, ZZ-CSQ fusion proteins with CSQ and an affinity protein (Z domain of protein A) capture antibodies and undergo multimerization and subsequent aggregation in response to calcium ions, enabling the antibody to be collected by affinity precipitation. After robustly validating and optimizing the performance of the platform, the ZZ-CSQ platform can rapidly purify therapeutic antibodies from industrial harvest feedstock with high purity (>97%) and recovery yield (95% ± 3%). In addition, the ZZ-CSQ platform outperforms protein A-based affinity chromatography (PAC) in removing impurities, yielding ∼20-fold less DNA and ∼4.8-fold less host cell protein (HCP) contamination. Taken together, this platform is rapid, recyclable, scalable, and cost-effective, and it shows antibody-purification performance superior or comparable to that of the standard affinity chromatography method.

Aggregating tags for column-free protein purification

Protein purification remains a central need for biotechnology. In recent years, a class of aggregating tags has emerged, which offers a quick, cost-effective and column-free alternative for producing recombinant proteins (and also peptides) with yield and purity comparable to that of the popular His-tag. These column-free tags induce the formation of aggregates (during or after expression) when fused to a target protein or peptide, and upon separation from soluble impurities, the target protein or peptide is subsequently released via a cleavage site. In this review, we categorize these tags as follows: (i) tags that induce inactive protein aggregates in vivo; (ii) tags that induce active protein aggregates in vivo; and (iii) tags that induce soluble expression in vivo, but aggregates in vitro. The respective advantages and disadvantages of these tags are discussed, and compared to the three conventional tags (His-tag, maltose-binding protein [MBP] tag, and intein-mediated purification with a chitin-binding tag [IMPACT-CN]). While this new class of aggregating tags is promising, more systematic tests are required to further the use. It is conceivable, however, that the combination of these tags and the more traditional columns may significantly reduce the costs for resins and columns, particularly for the industrial scale.

Partitioning in aqueous two-phase systems: Analysis of strengths, weaknesses, opportunities and threats

For half a century aqueous two-phase systems (ATPSs) have been applied for the extraction and purification of biomolecules. In spite of their simplicity, selectivity, and relatively low cost they have not been significantly employed for industrial scale bioprocessing. Recently their ability to be readily scaled and interface easily in single-use, flexible biomanufacturing has led to industrial re-evaluation of ATPSs. The purpose of this review is to perform a SWOT analysis that includes a discussion of: (i) strengths of ATPS partitioning as an effective and simple platform for biomolecule purification; (ii) weaknesses of ATPS partitioning in regard to intrinsic problems and possible solutions; (iii) opportunities related to biotechnological challenges that ATPS partitioning may solve; and (iv) threats related to alternative techniques that may compete with ATPS in performance, economic benefits, scale up and reliability. This approach provides insight into the current status of ATPS as a bioprocessing technique and it can be concluded that most of the perceived weakness towards industrial implementation have now been largely overcome, thus paving the way for opportunities in fermentation feed clarification, integration in multi-stage operations and in single-step purification processes.

Intein applications: from protein purification and labeling to metabolic control methods

The discovery of inteins in the early 1990s opened the door to a wide variety of new technologies. Early engineered inteins from various sources allowed the development of self-cleaving affinity tags and new methods for joining protein segments through expressed protein ligation. Some applications were developed around native and engineered split inteins, which allow protein segments expressed separately to be spliced together in vitro. More recently, these early applications have been expanded and optimized through the discovery of highly efficient trans-splicing and trans-cleaving inteins. These new inteins have enabled a wide variety of applications in metabolic engineering, protein labeling, biomaterials construction, protein cyclization, and protein purification.