Capsid ; Capsid Proteins ; Virus Assembly

Morphogenesis and maturation of viral particles is an essential step of viral replication. An infectious herpesviral particle has a multilayered architecture, and contains a large DNA genome, a capsid shell, a tegument and an envelope spiked with glycoproteins. Unique to herpesviruses, tegument is a structure that occupies the space between the nucleocapsid and the envelope and contains many virus encoded proteins called tegument proteins. Historically the tegument has been described as an amorphous structure, but increasing evidence supports the notion that there is an ordered addition of tegument during virion assembly, which is consistent with the important roles of tegument proteins in the assembly and egress of herpesviral particles. In this review we first give an overview of the herpesvirus assembly and egress process. We then discuss the roles of selected tegument proteins in each step of the process, i.e., primary envelopment, de-envelopment, secondary envelopment and transport of viral particles. We also suggest key issues that should be addressed in the near future.
Animals ; Herpesviridae ; physiology ; Herpesviridae Infections ; virology ; Humans ; Viral Proteins ; physiology ; Virus Assembly ; Virus Release

Hepatitis E is a main cause of acute viral hepatitis in developing countries where it occurs as sporadic cases and in epidemics form. The causative agent, hepatitis E virus, is transmitted primarily by the fecal-oral route. The approximately 7.5 kb positive-sense single-strand RNA genome includes three open reading frames (ORFs), one of which (ORF2) is postulated to encode the major viral capsid protein (pORF2) of 660 amino acid residues. We earlier showed that a bacterially expressed peptide, designated as NE2, located from amino acid residues 394 to 606 of ORF2, was found to aggregate into homodimer to at least hexamer. To understand the interface domains within this peptide vital for dimerization and formation of major neutralizing epitopes, NE2 protein underwent terminal-truncated and site-directed mutation. The hydrophobic region, ORF2 aa597-aa602 (AVAVLA), played a key role in oligomerization. Any amino acid residue of this region replaced with glutamic acid residue, the peptide can not refold as homodimer and/or oligomer. The immunoreactivities of these mutant peptides, blotted with anti-HEV neutralizing monoclonal antibody (8C11) and convalescent human sera, show associated to the formation of homodimer. The intermolecular contact region on homodimer was investigated by chemical cross-linking of two site-directed cysteines. When the alanine on aa597 site mutated with cysteine, two different homodimers were found in SDS-PAGE analysis. One (42kD) can be disassociated with 8mol/L urea, which is postulated to form by virtue of hydrophobic interaction, and the other (60kD) falls apart with the reductant DTT present. The exact conformation, generating the cross-linking reaction of cysteines, was further investigated by induced-oxidation on monomer and hydrophobic homodimer of A597C protein with GSH/GSSG. And the results revealed, it is the conformation of hydrophobic homodimer that induces the disulfide bond come into being, instead of the one of monomer. So the aa597 site was verified to be located on interface domain of hydrophobically interacting homodimeric complex. To evaluate the biological significance of hydrophobicity of interface domain, we searched natural variations as to the region on all available databases with NCBI blast program. All variations on these amino acid residues kept higher hydrophobicity, which suggests that the hydrophobic domain is critical for the assemblage and propagation of HEV. NE2 N-terminal deletions up to aa458 had no effect on dimerization and took no exact part in formation of major neutralizing epitopes, but the fragment may act as helper for the formation of major neutralizing epitopes on NE2. Interestingly, the C-terminus aa605-aa660 of ORF2 can also act as helper instead of the N-terminus of NE2. This study suggests an interface domain of NE2 might be vital for HEV capsomer assembly and formation of major neutralizing epitopes. These results may offer clues to the rational design of recombinant anti-HEV vaccine.
Capsid Proteins ; chemistry ; Hepatitis E virus ; chemistry ; Hydrophobic and Hydrophilic Interactions ; Protein Multimerization ; Protein Structure, Tertiary ; Virus Assembly

The special nucleic acid fragments, 5' untranslated region (5' UTR) and internal ribosome entry site (IRES) of foot-and-mouth disease virus (FMDV), which interact with the capsid proteins, were selected as scaffolds to investigate the assembly efficiency of foot-and-mouth disease (FMD) virus-like particles (VLPs). The assembled product was characterized by evaluation of particle size, surface potential, gel retardation assay, nuclease digestion experiments, size-exclusion chromatography, transmission electron microscopy and circular dichroism analysis. The results confirmed that the 5' UTR and IRES of FMDV co-assembled with the FMD VLPs and facilitated the assembly efficiency of FMD-VLPs. It demonstrates that the assembly efficiency of 75S particles of VLPs-5'UTR was significantly higher than those of the VLPs (P<0.001) and VLPs-IRES group (P<0.01). Comparatively the assembly efficiency of 12S particles of VLPs-IRES was significantly higher than those of the VLPs (P<0.000 1) and VLPs-5'UTR (P<0.000 1). It showed that the 5' UTR represented more effective in facilitating the assembly of VLPs. This study proposes an optimized strategy for improving the assembly efficiency of VLPs for the development of VLPs vaccine.
5' Untranslated Regions ; Capsid Proteins/metabolism* ; Foot-and-Mouth Disease Virus/physiology* ; Internal Ribosome Entry Sites ; Nucleic Acids/metabolism* ; Virus Assembly

OBJECTIVETo explore the possibility of using HBV as a gene delivery vector, and to test the anti-HBV effects by intracellular combined expression of antisense RNA and dominant negative mutants of core protein.

METHODSFull length of mutant HBV genome, which expresses core-partial P fusion protein and/or antisense RNA, was transfected into HepG2.2.15 cell lines. Positive clones were selected and mixed in respective groups with hygromycin in the culture medium. HBsAg and HBeAg, which exist in the culture medium, were tested by ELISA method. Intracellular HBc related HBV DNA was examined by dot blot hybridization. The existence of recombinant HBV virion in the culture medium was examined by PCR. Free of packaging signal, HBV genome, which express the HBV structural proteins including core, pol and preS/S proteins, was inserted into pCI-neo vector. HepG2 cell lines were employed to transfect with the construct. G418 selection was done at the concentration of 400mug/ml in the culture medium. The G418-resistant clones with the best expression of HBsAg and HBcAg were theoretically considered as packaging cell lines and propagated under the same conditions. It was transfected with plasmid pMEP-CPAS and then selected with G418 and hygromycin in the culture medium. The existence of recombinant HBV virion in the culture medium was examined by PCR.

RESULTSThe mean inhibitory rates of HBsAg were 2.74% 3.83%, 40.08 2.05% (t=35.5, P<0.01), 66.54% 4.45% (t=42.3, P<0.01), and 73.68% 5.07% (t=51.9, P<0.01) in group 2.2.15-pMEP4, 2.2.15-CP, 2.2.15-SAS, and 2.2.15-CPAS, respectively. The mean inhibitory rates of HBeAg were 4.46% 4.25%, 52.86% 1.32% (t=36.2, P<0.01), 26.36% 1.69% (t=22.3, P<0.01), and 59.28% 2.10% (t=39.0, P<0.01), respectively. The inhibitory rates of HBc related HBV DNA were 0, 82.0%, 59.9%, and 96.6%, respectively. Recombinant HB virion was detectable in the culture medium of all the three treatment groups. G418-resistant HBV packaging cell line, which harbored an HBV mutant whose packaging signal had been deleted, was generated. Expression of HBsAg and HBcAg was detectable. Transfected with plasmid pMEP-CPAS, it was found to secrete recombinant HB virion and no wild-type HBV was detectable in the culture medium.

CONCLUSIONSIt has stronger anti-HBV effects by combined expression of antisense RNA and dominant negative mutants than by individual expression of them. With the help of wild-type HBV, the modified HBV genome can form and secret HBV like particles, which provides evidence that the antiviral gene will be hepatotropic expression and the antiviral effects will be amplified. The packaging cell line can provide packaging for replication-defective HBV, but with low efficiency.

Cell Line ; Genetic Engineering ; Genetic Vectors ; Hepatitis B virus ; genetics ; Mutation ; Plasmids ; RNA, Antisense ; physiology ; Transfection ; Viral Core Proteins ; physiology ; Virus Assembly ; Virus Replication

In eukaryotic cells, multivesicular bodies (MVBs) are required for trafficking of membrane proteins to lysosomes for selective destruction. The sorting of ubiquitylated membrane proteins into multivesicular bodies and the biogenesis of MVBs are mediated by the endosomal sorting complex required for transport (ESCRT). Topologically equivalent to the budding of intralumenal vesicles from the limiting membrane of the MVBs, the ESCRT complex is also involved in cytokinetic abscission, phagophore formation, and enveloped virus budding. Many retroviruses and RNA viruses encode "late-domain" motifs that are able to interact with the components of the ESCRT complex, and the interactions recruit ESCRT-III and VPS4 to the viral assembly and budding sites. Recently, few studies revealed that the ESCRT complex is also required for efficient egress of some DNA viruses, including Hepatitis B, Herpes simplex virus type-1, and Autographa californica multiple nucleopolyhedrovirus. Further examination of virus-ESCRT interactions should shed light on the detailed mechanism of virus assembly and budding.
Endosomal Sorting Complexes Required for Transport ; physiology ; Humans ; Viral Envelope Proteins ; metabolism ; Virus Assembly ; Virus Physiological Phenomena ; Virus Release ; Viruses ; growth & development

In order to make clear the packing mechanism of the BmNPV polyhedra, a polyhedrin gene negative recombinant baculovirus, vBmBac(polh-)-5B-EGFP, expressing EGFP was constructed, and used to infect BmN cells jointly with wild-type BmNPV. Fluorescent microscopic observation demonstrated that EGFP and polyhedrin were expressed simultaneously, and the EGFP expression and polyhedra formation occurred in most of the jointly infected cells. Analysis of the purified polyhedra from jointly infected BmN cells showed that the foreign proteins were present in the polyhedra. The results indicated that BmNPV polyhedrin could incorporate proteins other than viral proteins into the polyhedra. It implies that a nonspecific recognition mechanism exists in the embedment of BmNPV polyhedra.
Animals ; Bombyx ; Gene Expression ; Green Fluorescent Proteins ; genetics ; metabolism ; Nucleopolyhedrovirus ; genetics ; physiology ; Viral Structural Proteins ; genetics ; metabolism ; Virus Assembly

This investigation is to delete the most of the coding sequence (1104 bp) of the IV a2 gene in an adenovirus genome by a lambda-Red recombinase system-mediated PCR-targeting approach and rescue a recombinant adenovirus with IV a2 deletion. First, the template pAK of PCR targeting, containing kanamycin cassette, was constructed. Then, a linear fragment for PCR targeting, which had 39 bp homologous arms at both of its terminus, was amplified by PCR from the pAK. The pFG140 and the linear fragment were electroporated into E. coli BW25113/pIJ790 sequentially and the recombinant pFG140-deltaIV a2 (1104) was established by homologous recombination between the linear fragment and the pFG140 with aid of X-Red recombinase. The precise deletion of 1 104 bp fragment from IV a2 was confirmed by restriction endonucleases digestion and DNA sequencing. ORF of IV a2 was amplified by PCR from pFG140 and then cloned into the pAAV2neo vector. The recombinant adenovirus Ad5delta IV a2 (1104) was rescued by co-transfection of pFG140-deltaIV a2 (1104) and pAAV2neo-IV a2 into HEK293 cells. It was shown by Western Blot that IV a2 could not be detected in the Ad5deltaIV a2 (1104)- infected HEK293 cells. This study established a PCR-targeting strategy for manipulating adenovirus genome directly by a lambda-Red recombinase system, and a recombinant adenovirus with IV a2 deletion was obtained.
Adenoviridae ; genetics ; Genome, Viral ; HEK293 Cells ; Humans ; Polymerase Chain Reaction ; Recombinases ; metabolism ; Sequence Deletion ; Viral Proteins ; genetics ; Virus Assembly

Recombinant adeno-associated viral vectors (rAAV) have been widely used as gene therapy vectors in clinical trials. Here, we reviewed the genomic structures and replication mechanisms of wt-AAV. Then, the assembly of capsid and the encapsidation of genomic DNA, two major events during AAV pakaging, was discussed in detail. Although the overall pattern of virus assembly and encapsidation is known, the molecular mechanisms and the structure-function relationship involved in these processes are not well understood. Further elucidatation of these processes may improve the production technology of rAAV and develop gene drug based on rAAV.
Capsid ; physiology ; Capsid Proteins ; genetics ; DNA, Viral ; genetics ; Dependovirus ; genetics ; physiology ; Genetic Vectors ; Genome, Viral ; Virus Assembly ; genetics ; physiology

Ebola virus (EBOV) is a key member of Filoviridae family and causes severe human infectious diseases with high morbidity and mortality. As a typical negative-sense single-stranded RNA (-ssRNA) viruses, EBOV possess a nucleocapsid protein (NP) to facilitate genomic RNA encapsidation to form viral ribonucleoprotein complex (RNP) together with genome RNA and polymerase, which plays the most essential role in virus proliferation cycle. However, the mechanism of EBOV RNP formation remains unclear. In this work, we solved the high resolution structure of core domain of EBOV NP. The polypeptide of EBOV NP core domain (NP(core)) possesses an N-lobe and C-lobe to clamp a RNA binding groove, presenting similarities with the structures of the other reported viral NPs encoded by the members from Mononegavirales order. Most strikingly, a hydrophobic pocket at the surface of the C-lobe is occupied by an α-helix of EBOV NP(core) itself, which is highly conserved among filoviridae family. Combined with other biochemical and biophysical evidences, our results provides great potential for understanding the mechanism underlying EBOV RNP formation via the mobility of EBOV NP element and enables the development of antiviral therapies targeting EBOV RNP formation.
Crystallography, X-Ray ; Ebolavirus ; physiology ; Humans ; Nucleoproteins ; chemistry ; genetics ; metabolism ; Protein Structure, Tertiary ; Structure-Activity Relationship ; Virus Assembly ; physiology