Identification of mimotopes of the Japanese encephalitis virus envelope protein using phage-displayed combinatorial peptide library

Filamentous bacteriophages, natural nanoparticles, for viral vaccine strategies

Filamentous bacteriophages are natural nanoparticles formed by the self-assembly of structural proteins that have the capability of replication and infection. They are used as a highly efficient vaccine platform to enhance immunogenicity and effectively stimulate the innate and adaptive immune response. Compared with traditional vaccines, phage-based vaccines offer thermodynamic stability, biocompatibility, homogeneity, high carrying capacity, self-assembly, scalability, and low toxicity. This review summarizes recent research on phage-based vaccines in virus prevention. In addition, the expression systems of filamentous phage-based virus vaccines and their application principles are discussed. Moreover, the prospect of the prevention of emerging infectious diseases, such as coronavirus 2019 (COVID-19), is also discussed.

Phage display as a promising approach for vaccine development

Bacteriophages are specific antagonists to bacterial hosts. These viral entities have attracted growing interest as optimal vaccine delivery vehicles. Phages are well-matched for vaccine design due to being highly stable under harsh environmental conditions, simple and inexpensive large scale production, and potent adjuvant capacities. Phage vaccines have efficient immunostimulatory effects and present a high safety profile because these viruses have made a constant relationship with the mammalian body during a long-standing evolutionary period. The birth of phage display technology has been a turning point in the development of phage-based vaccines. Phage display vaccines are made by expressing multiple copies of an antigen on the surface of immunogenic phage particles, thereby eliciting a powerful and effective immune response. Also, the ability to produce combinatorial peptide libraries with a highly diverse pool of randomized ligands has transformed phage display into a straightforward, versatile and high throughput screening methodology for the identification of potential vaccine candidates against different diseases in particular microbial infections. These libraries can be conveniently screened through an affinity selection-based strategy called biopanning against a wide variety of targets for the selection of mimotopes with high antigenicity and immunogenicity. Also, they can be panned against the antiserum of convalescent individuals to recognize novel peptidomimetics of pathogen-related epitopes. Phage display has represented enormous promise for finding new strategies of vaccine discovery and production and current breakthroughs promise a brilliant future for the development of different phage-based vaccine platforms.

Japanese encephalitis virus NS2B-NS3 protease binding to phage-displayed human brain proteins with the domain of trypsin inhibitor and basic region leucine zipper

Flavivirus NS2B-NS3 proteases are associated with neurovirulence, becoming an important target for insight into the virus-induced pathogenesis. In this study, a phage-displayed human brain cDNA library was used to detect possible interaction between brain proteins and the Japanese encephalitis virus (JEV) NS2B-NS3 protease. After six rounds of biopanning, eight high-affinity NS2B-NS3 protease-interacting phages were identified. Identified NS2B-NS3 protease-interacting brain proteins contained several repeats of the consensus motifs E(R/K)(R/K)K and G(R/K)(R/K) with the dibasic residues, being similar to the conserved cleavage sites among flavivirus proteases. In addition, three identified brain proteins (phage-24, 34, and 44) were predicted as the domain of trypsin inhibitor and basic region leucine zipper (bZIP) using the SMART genome search. Immunoprecipitation and cleavage of two brain fusion proteins (phage-24 and phage-46) by the NS2B-NS3 protease confirmed the specific interaction between identified brain proteins and the JEV NS2B-NS3 protease. Fluorogenic peptide substrate assays revealed dose-manner inhibitory effects of these two brain fusion proteins on the trans-cleavage activity of NS2B-NS3 protease. Moreover, in vitro signaling pathway assay revealed that the JEV NS2B-NS3 protease significantly inhibited the signaling pathway of activator protein 1(AP1), a member of the bZIP family. Our results provide an insight into the protein interaction network of the JEV NS2B-NS3 protease in human brain.

Binding interaction of SARS coronavirus 3CL(pro) protease with vacuolar-H+ ATPase G1 subunit

The pathogenesis of severe acute respiratory syndrome coronavirus (SARS-CoV) is an important issue for treatment and prevention of SARS. Recently, SARS-CoV 3CL(pro) protease has been implied to be possible relevance to SARS-CoV pathogenesis. In this study, we intended to identify potential 3CL(pro)-interacting cellular protein(s) using the phage-displayed human lung cDNA library. The vacuolar-H+ ATPase (V-ATPase) G1 subunit that contained a 3CL(pro) cleavage site-like motif was identified as a 3CL(pro)-interacting protein, as confirmed using the co-immunoprecipitation assay and the relative affinity assay. In addition, our result also demonstrated the cleavage of the V-ATPase G1 fusion protein and the immunoprecipitation of cellular V-ATPase G1 by the 3CL(pro). Moreover, loading cells with SNARF-1 pH-sensitive dye showed that the intracellular pH in 3CL(pro)-expressing cells was significantly lower as compared to mock cells.