A simple and high efficiency purification of His-tagged turnip yellow mosaic virus-like particle (TYMV-VLP) by nickel ion affinity precipitation

Virus-like particles (VLPs) is one of the most favourable subjects of study, especially in the field of nanobiotechnology and vaccine development because they possess good immunogenicity and self-adjuvant properties. Conventionally, VLPs can be tagged and purified using affinity chromatography or density gradient ultracentrifugation which is costly and time-consuming. Turnip yellow mosaic virus (TYMV) is a plant virus, where expression of the viral coat protein (TYMVc) in Escherichia coli (E. coli) has been shown to form VLP. In this study, we report a non-chromatographic method for VLP purification using C-terminally His-tagged TYMVc (TYMVcHis₆) as a protein model. Firstly, the TYMVcHis₆ was cloned and expressed in E. coli. Upon clarification of cell lysate, nickel (II) chloride [NiCl₂; 15 µM or equivalent to 0.0000194% (w/v)] was added to precipitate TYMVcHis₆. Following centrifugation, the pellet was resuspended in buffer containing 1 mM EDTA to chelate Ni²⁺, which is then removed via dialysis. A total of 50% of TYMVcHis₆ was successfully recovered with purity above 0.90. Later, the purified TYMVcHis₆ was analysed with sucrose density ultracentrifugation, dynamic light scattering (DLS), and transmission electron microscopy (TEM) to confirm VLP formation, which is comparable to TYMVcHis₆ purified using the standard immobilized metal affinity chromatography (IMAC) column. As the current method omitted the need for IMAC column and beads while significantly reducing the time needed for column washing, nickel affinity precipitation represents a novel method for the purification of VLPs displaying poly-histidine tags (His-tags).