By using the modified ITC, ELPylated Cap protein was purified to more than 90% purity, which was comparable to that of His-tagged Cap protein purified by nickel affinity chromatography. After obtaining the purified fusion protein, we tried to cleave ELP tag from ELPylated Cap protein with recombinant TEV protease. antibody, cytokine responses and immunoprotection against PCV2 challenge were compared. Results ELPylated Cap protein was expressed as a soluble protein and purified to 94.3% purity by ITC in the presence of 1% Triton X-100 and 0.5?M urea. His-tagged Cap fusion protein was expressed as insoluble inclusion bodies and purified to 90% purity under denatured conditions. The two purified fusion proteins assembled into VLP with comparable morphology. Compared to immunization with VLP, immunization with ELP-VLP induced significantly (or baculovirus system, which requires expensive ultracentrifugation or chromatography for purification [5, 6]. Therefore, reduction of PCV2 vaccine production cost is a key priority for veterinary research. Elastin-like polypeptides (ELP) are derivatives of tropoelastin with the pentapeptide (Val-Pro-Gly-Xaa-Gly) repeats, where Xaa can be any amino acid except proline. ELP have a unique house, inverse phase transition, which allows temperature-dependent reversible change from soluble monomers to insoluble aggregates [7, 8]. Fusion of ELP with a target protein at the genetic level is now termed ELPylation, which has been exploited for several biomedical applications, such as recombinant protein purification [9], drug delivery [10] and protein half-life extension [11]. Like ELP, ELPylated proteins can be purified by inverse transition cycling (ITC) with the advantages of simplicity and low cost. Since they are derived from tropoelastin, ELP are biocompatible, non-toxic and non-immunogenic, making ELPylated proteins suitable for in vivo applications [12]. More recently, ELPylation has been used to improve the immunogenicity of influenza computer virus M protein [13] and hemagglutinin [14]. In the present study, we explored the feasibility of ELPylation technology for simple purification and immunogenicity improvement of Aripiprazole (D8) PCV2 VLP. The Cap protein of PCV2b, together with the computer virus neutralizing (VN) epitopes of PCV2a, PCV2d and PCV2e, was expressed in as an ELPylated protein, and purified to a high purity with altered ITC. For the control purpose, the Cap protein was also expressed as a His-tagged protein and purified by nickel affinity chromatography. Both ELPylated and His-tagged Cap proteins assembled into VLP with comparable morphology. Immunization of mice showed that ELPylated VLP was more immunogenic than His-tagged VLP. To NOL7 our knowledge, this is the first study to demonstrate that ELPylation can be used for VLP preparation and immunogenicity improvement. Materials and methods Vector construction ELP fusion expression vector pET-ELP was constructed by cloning ELP coding sequence into pET-30a (+) vector (Novagen, USA) with codon usage using JAVA Codon Adaption Tool [17]. The Aripiprazole (D8) synthetic sequence, with a tobacco etch computer virus (TEV) protease recognition signal introduced at the 5 end, was cloned into pET-ELP vector with before IPTG induction (1), after IPTG induction (2), supernatants (3) and pellets (4) of centrifuged cell lysates were analyzed by Aripiprazole (D8) 12% SDS-PAGE. M indicates protein molecular mass marker. The small arrows indicate ELP-Cap and Cap-His fusion proteins Protein expression Both pELP-Cap and pET-Cap vectors were transformed individually into BL21 (DE3) as a fusion protein with self-aggregating peptide ELK16 and purified by centrifugation in the presence of 0.5% Triton X-100 as previously described [19]. The purified ELPylated Cap protein (100?g) was digested overnight with the recombinant protease (30?g) as previously described [19]. After digestion, the active aggregates of TEV protease were removed by centrifugation and the cleaved ELP tag was removed by one round of ITC as described. Transmission electron microscopy Both ELPylated and His-tagged Cap proteins (25?g) were absorbed onto copper grids (400 meshes) for 2.5?min at room temperature. After drying gently with filter paper, the grids were stained with 3% phosphotungstic acid for 2.5?min. The excess liquid was removed and the samples were observed under transmission electron microscope (Philips, Tecnai 12, Netherland) at an acceleration voltage of 75?kV. Western blotting Both ELPylated VLP (ELP-VLP) and His-tagged VLP (VLP) were separated on 12% SDS-PAGE and transferred to nitrocellulose membrane (Merck, USA) using a Mini-Protean? Tetra Cell (Bio-Rad, USA) by following the manufacturers training. The membrane was blocked for 2?h at 37?C with 5% skim milk powder in PBST.
