In vivo enzymatic digestion of HRV 3C protease cleavage sites-containing proteins produced in a silkworm-baculovirus expression system

Carrier proteins boost expression of PR-39-derived peptide in Pichia pastoris

AIMS

Multidrug resistance presents difficulties in preventing and treating bacterial infections. Proline-rich antimicrobial peptides (PrAMPs) inhibit bacterial growth by affecting the intracellular targets rather than by permeabilizing the membrane. The aim of this study was to develop a yeast-based fusion carrier system using calmodulin (CaM) and xylanase (XynCDBFV) as two carriers to express the model PrAMP PR-39-derived peptide (PR-39-DP) in Pichia pastoris.

METHODS AND RESULTS

Fusion protein secreted into the culture supernatant was purified in a one-step on-column digestion using human rhinovirus 3C protease, obtaining the target peptide PR-39-DP. The growth curves of Escherichia coli were monitored by recording the OD600 values of the bacteria. The antibacterial activity of PR-39-DP was evaluated in killing assays performed on E. coli. The yield of PR-39-DP was 1.0-1.2 mg l-1 in the CaM fusion carrier system, approximately three times that of the XynCDBFV fusion carrier system. The minimal inhibitory concentration of PR-39-DP was ∼10.5 µg ml-1.

CONCLUSIONS

CaM and XynCDBFV provide increased stability and promote the expression and secretion of active PR-39-DP.

Display of multiple proteins on engineered canine parvovirus-like particles expressed in cultured silkworm cells and silkworm larvae

Recent progress has been made dramatically in decorating virus-like particles (VLPs) on the surface or inside with functional molecules, such as antigens or nucleic acids. However, it is still challenging to display multiple antigens on the surface of VLP to meet the requirement as a practical vaccine candidate. Herein this study, we focus on the expression and engineering of the capsid protein VP2 of canine parvovirus for VLP display in the silkworm-expression system. The chemistry of the SpyTag/SpyCatcher (SpT/SpC) and SnoopTag/SnoopCatcher (SnT/SnC) are efficient protein covalent ligation systems to modify VP2 genetically, where SpyTag/SnoopTag are inserted into the N-terminus or two distinct loop regions (Lx and L2) of VP2. The SpC-EGFP and SnC-mCherry are employed as model proteins to evaluate their binding and display on six SnT/SnC-modified VP2 variants. From a series of protein binding assays between indicated protein partners, we showed that the VP2 variant with SpT inserted at the L2 region significantly enhanced VLP display to 80% compared to 5.4% from N-terminal SpT-fused VP2-derived VLPs. In contrast, the VP2 variant with SpT at the Lx region failed to form VLPs. Moreover, the SpT (Lx)/SnT (L2) double-engineered chimeric VP2 variants showed covalent conjugation capacity to both SpC/SnC protein partners. The orthogonal ligations between those binding partners were confirmed by both mixing purified proteins and co-infecting cultured silkworm cells or larvae with desired recombinant viruses. Our results indicate that a convenient VLP display platform was successfully developed for multiple antigen displays on demand. Further verifications can be performed to assess its capacity for displaying desirable antigens and inducing a robust immune response to targeted pathogens.

Virus-like particles vaccines based on glycoprotein E0 and E2 of bovine viral diarrhea virus induce Humoral responses

Bovine viral diarrhea/mucosal disease (BVD/MD) is a viral infectious disease that seriously endangers the health of cattle herds and brings serious economic losses to the global cattle industry. Virus-like particles (VLPs) are empty shell structures without viral nucleic acid, which are similar to natural virus particles in morphology and structure. Because of their strong immunogenicity and biological activity, some of them have been used as vaccines in clinical trials. In this study, we developed a strategy to generate BVDV (E0 + E2, E2 + E2) VLPs using an insect baculovirus expression vector system (BEVS). The VLPs obtained were detected by immunofluorescence assay (IFA), western blotting analyses and transmission electron microscope (TEM), and the results showed that VLPs of high purity were obtained. Mice immunized with VLPs (15  μg) and Freund's adjuvant (100  μl) elicited higher BVDV-neutralizing antibody in comparison with Freund's adjuvant control (p < 0.0001), and even on day 21 or 35 post-prime immunization, the neutralizing antibody levels of mice immunized with E0 + E2 or E2 + E2 VLPs were significantly higher compared with inactivated vaccine (p < 0.05). A subsequent challenge reveals that the viral loads of livers, kidneys, spleens, lungs and small intestines were significantly lower compared with control (p < 0.0001), and the viral loads of mice immunized with E0 + E2 or E2 + E2 VLPs in the small intestines were significantly lower compared with inactivated vaccine (p < 0.05). Thus, VLPs are a promising candidate vaccine and warrants further clinical evaluation.