Detection and quantification of transition metal leaching in metal affinity chromatography with hydroxynaphthol blue

Chromatographic purification of histidine-tagged proteins using zirconia particles modified with phosphate groups

Immobilized metal ion affinity chromatography (IMAC) is one of the most common purification techniques for histidine-tagged proteins (His-tagged proteins). IMAC enables the purification of His-tagged proteins at high purity on the basis of coordination bonds between His-tags and metal ions (such as Ni²⁺, Co²⁺, and Cu²⁺) immobilized on the matrices in columns. However, IMAC requires low-pH solutions or high-concentration imidazole solutions for eluting His-tagged proteins, which can affect protein conformation and activity. The present study provides a His-tagged protein purification method using zirconia particles modified with phosphate groups. This method is based on the electrostatic attractions between a His-tag moiety of proteins and phosphate groups on the zirconia particles; this method requires only high-concentration salt solutions at pH 7.0 for eluting the proteins. A column packed with phosphate-modified zirconia particles was demonstrated to enable the purification of two model His-tagged proteins-His-tagged green fluorescent protein and His-tagged alkaline phosphatase fused with maltose binding protein. Thus, this chromatography method is useful for purifying His-tagged proteins without any pH stress or additives. Additionally, because of the mechanical properties of the zirconia particles, this technique enables high-performance purification at a high flow rate.

Purification of a Hydrophobic Elastin-Like Protein Toward Scale-Suitable Production of Biomaterials

Elastin-like proteins (ELPs) are polypeptides with potential applications as renewable bio-based high-performance polymers, which undergo a stimulus-responsive reversible phase transition. The ELP investigated in this manuscript—ELP[V2Y-45]—promises fascinating mechanical properties in biomaterial applications. Purification process scalability and purification performance are important factors for the evaluation of potential industrial-scale production of ELPs. Salt-induced precipitation, inverse transition cycling (ITC), and immobilized metal ion affinity chromatography (IMAC) were assessed as purification protocols for a polyhistidine-tagged hydrophobic ELP showing low-temperature transition behavior. IMAC achieved a purity of 86% and the lowest nucleic acid contamination of all processes. Metal ion leakage did not propagate chemical modifications and could be successfully removed through size-exclusion chromatography. The simplest approach using a high-salt precipitation resulted in a 60% higher target molecule yield compared to both other approaches, with the drawback of a lower purity of 60% and higher nucleic acid contamination. An additional ITC purification led to the highest purity of 88% and high nucleic acid removal. However, expensive temperature-dependent centrifugation steps are required and aggregation effects even at low temperatures have to be considered for the investigated ELP. Therefore, ITC and IMAC are promising downstream processes for biomedical applications with scale-dependent economical costs to be considered, while salt-induced precipitation may be a fast and simple alternative for large-scale bio-based polymer production.